University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Determination of local magnitude scale, ML, for north-west Iran using acceler Determination of local magnitude scale, ML, for north-west Iran using acceler 1 14 35595 10.22059/jesphys.2013.35595 FA Mahboubeh Sharifi M.Sc. Student of Geophysics, Earth Physics Department, Institute of Geophysics University of Tehran, Iran Esmaeil Bayramnejad Assistant Professor of Geophysics, Earth Physics Department, Institute of Geophysics University of Tehran, Iran Zaher Hossein Shomali Associate Professor of Geophysics, Earth Physics Department, Institute of Geophysics University of Tehran, Iran Journal Article 2012 05 27 *نگارنده رابط: تلفن: 61118230-021 دورنگار: 88630479-021 E-mail:ebayram@ut.ac.ir According to accelerograms that do not clip in small distances unlike seismograms, results for local magnitude estimation can be more acceptable than that from seismogram data. The dataset used in this study contains 780 two-component horizontal accelerograms from 390 earthquakes with magnitudes range Mn ≤ 4. To enhance the quality of the data, we employed baseline correction. We processed the uncorrected strong-motion data to make baseline and instrument correction and band-pass filtering. The local magnitude introduced by Richter (1935) is based on the amplitude recorded by the Wood-Anderson torsion seismograph with a natural period of 0.8 sec, a damping constant of h=0.8, and a static magnification, v=2800. Richter chose his reference earthquake with ML=3, such that amplitude was 1 mm on a Wood-Anderson seismograph at an epicentral distance of 100 km. He determined –log A0 attenuation function for southern California region. Log A0 depends on the effects of geometrical spreading and an elastic attenuation and also these effects depend on the characteristics of the crustal structure (Bakun and Joyner, 1984). For large variability of velocity and attenuation, structure of the Earth’s crust does not permit to develop a unique calibration function for local events. Therefore, it is necessary to calibrate it for any region. In this article, we calibrate ML for northwest Iran using synthetic Wood-Anderson seismograms. The area under study extends from 36 to 40 degrees north latitude and from 44 to 50 degrees east longitude. The local magnitude is determined within the period range of greatest engineering interest. So it is a very useful scale for engineering. Many structures have natural periods close to that of a Wood-Anderson instrument, and the extent of earthquake damage is closely related to ML. Nowadays, the lack of W-A Seismograph prevents the calculation of such magnitude in the original form. Kanamori and Jennings (1978) proposed an alternative method of calculation. The accelerograph records are used as acceleration input to an oscillator with characteristics of the Wood-Anderson instrument to produce a synthetic seismogram. Measurements of peak amplitudes on Wood-Anderson instruments were studied to determine a distance correction curve for use in determining the local magnitude ML. We also use the approach suggested by Hutton and Boore (1987) to invert for the empirical distance-correction function in the local magnitude scales. The distance – correction function can be expressed as: -log Aij = n log )rij / 100( +K )rij -100+ (3.0 - MLi + Sj , where the n and k are parameters related to the geometrical spreading and an elastic attenuation. Aij is the horizontal maximum amplitude of the ith event observed at the jth station component, rij is the hypocentral distance from the ith event to the jth station component, MLi is the local magnitude of the ith event, and Sj is the correction factor for the jth station component. The n=1, is appropriate for body-wave propagation in homogeneous media, but the earth is not perfectly elastic and seismic waves attenuate or decrease in amplitude as they propagate. The geometrical spreading and an elastic attenuation can also reduce wave amplitudes. The above Equation can be cast into a standard matrix formation: Gm=d, which represents a typical linear inversion problem in geophysics that can be solved using least-squares or generalized inversion methods. First we used generalized inverse method to calculate the attenuation relationship but we found a negative an elastic attenuation coefficient which is not correct physically. Negative value of k indicates that the assumption of a simple shape for the attenuation curve, with a constant geometrical spreading for different distances is not correct. At the closest ranges, the direct arrival dominates the waveform; but at larger ranges, the rays reflected from boundaries and all of the energy is reflected upward, so postcritical reflections become more important. The range at which the Moho reflection becomes postcritical is indicated by the abrupt increase in amplitude of that ray (Burger et al., 1987). So we performed the trilinear form of attenuation on the data (Atkinson and Mereu, 1992) to avoid the negative values of k. We used Monte Carlo technique to evaluate distance correction curves for north-westIran, and testing all possible combination that minimizes the average residual errors. Results show that we have 3 values for geometrical spreading. Apparent geometric spreading depends on the geometry of spreading in a layered crust, which is a function of distance, but anelasticity is independent of distance. These three values for geometrical spreadings are: R ≤ 85 km, n1 = 0.73; 85 >R≤ 120 km, n2 = -0.46; R>120 km, n3 = 0.22; k =0.00037 The distances less than 85 km related to direct waves. Note that distance ranges between 85 and 120 km is the distance where the Moho reflection becomes postcritical and is indicated by the abrupt increase in amplitude. The focal depth, crustal thickness, and the crustal velocity gradient have important influences on the range at which the amplitude increases. The result of ground motion in north-west Iran demonstrates that crustal structure can influence the strong motion attenuation relations. The uniform distribution of the residuals about their baselines (Fig. 4) show that the trilinear distance attenuation relation developed in this study provide more reliable estimates of ML values than those from linear relation. ML values using the linear distance attenuation are overestimated at distance larger than about 85 km (Fig. 3). We used trilinear method to estimate the local magnitude, but distance attenuation is independent from crustal structure. The attenuation along the energy ray path and the site geology conditions play roles of great importance in the recorded amplitudes. In the process of magnitude calculation, such effects are reduced if a proper attenuation function and magnitude station corrections are applied, so we applied the station correction on the amplitudes and performed a linear regression analysis on the data to obtain n and k.The results represent a logical response. No trend is evident on the distribution of residual in the corrected linear method, thus the attenuation function determined in this study does not depend on geology variation or hypocentral distances, as it works well for the north-west Iran region. The distance – correction and local magnitude function can be expressed as: -Log A0 = (1.52±0.0057) log(r/100) + (0.00137±3.20E-07) (r-100) + 3, ML = log A + (1.52 ± 0.0057) log(r/100) + (0.0013 ± 3.20E-07) (r-100) +3, The parameter k can be related to the inelastic attenuation coefficient Q using the Bakun and Joyner (1984) formula γ = ln 10k = πf/QVS, where VS is the average crustal S-wave velocity. Taking an average S wave of VS = 3.4 km /s, the k ≈ 0.00137 value obtained in the present study introduces a value of γ = k ln (10) = 0.00317 and Q(1 Hz) = 280. Nuttli (1980) found that a γ value of 0.0045 km -1 (between 0.003 and 0.006) corresponds to an apparent Q of 200 (between 152 and 303) for Sg. The γ and Q value agree with the result given by Nuttli. He showed that the attenuation of 1-sec period crustal phases in Iran is relatively high. The high attenuation value is due to the tectonic complexity and the widespread young volcanics in the region. This result should be treated with caution, because the maximum amplitude data do not necessarily correspond to a single seismic phase . *نگارنده رابط: تلفن: 61118230-021 دورنگار: 88630479-021 E-mail:ebayram@ut.ac.ir According to accelerograms that do not clip in small distances unlike seismograms, results for local magnitude estimation can be more acceptable than that from seismogram data. The dataset used in this study contains 780 two-component horizontal accelerograms from 390 earthquakes with magnitudes range Mn ≤ 4. To enhance the quality of the data, we employed baseline correction. We processed the uncorrected strong-motion data to make baseline and instrument correction and band-pass filtering. The local magnitude introduced by Richter (1935) is based on the amplitude recorded by the Wood-Anderson torsion seismograph with a natural period of 0.8 sec, a damping constant of h=0.8, and a static magnification, v=2800. Richter chose his reference earthquake with ML=3, such that amplitude was 1 mm on a Wood-Anderson seismograph at an epicentral distance of 100 km. He determined –log A0 attenuation function for southern California region. Log A0 depends on the effects of geometrical spreading and an elastic attenuation and also these effects depend on the characteristics of the crustal structure (Bakun and Joyner, 1984). For large variability of velocity and attenuation, structure of the Earth’s crust does not permit to develop a unique calibration function for local events. Therefore, it is necessary to calibrate it for any region. In this article, we calibrate ML for northwest Iran using synthetic Wood-Anderson seismograms. The area under study extends from 36 to 40 degrees north latitude and from 44 to 50 degrees east longitude. The local magnitude is determined within the period range of greatest engineering interest. So it is a very useful scale for engineering. Many structures have natural periods close to that of a Wood-Anderson instrument, and the extent of earthquake damage is closely related to ML. Nowadays, the lack of W-A Seismograph prevents the calculation of such magnitude in the original form. Kanamori and Jennings (1978) proposed an alternative method of calculation. The accelerograph records are used as acceleration input to an oscillator with characteristics of the Wood-Anderson instrument to produce a synthetic seismogram. Measurements of peak amplitudes on Wood-Anderson instruments were studied to determine a distance correction curve for use in determining the local magnitude ML. We also use the approach suggested by Hutton and Boore (1987) to invert for the empirical distance-correction function in the local magnitude scales. The distance – correction function can be expressed as: -log Aij = n log )rij / 100( +K )rij -100+ (3.0 - MLi + Sj , where the n and k are parameters related to the geometrical spreading and an elastic attenuation. Aij is the horizontal maximum amplitude of the ith event observed at the jth station component, rij is the hypocentral distance from the ith event to the jth station component, MLi is the local magnitude of the ith event, and Sj is the correction factor for the jth station component. The n=1, is appropriate for body-wave propagation in homogeneous media, but the earth is not perfectly elastic and seismic waves attenuate or decrease in amplitude as they propagate. The geometrical spreading and an elastic attenuation can also reduce wave amplitudes. The above Equation can be cast into a standard matrix formation: Gm=d, which represents a typical linear inversion problem in geophysics that can be solved using least-squares or generalized inversion methods. First we used generalized inverse method to calculate the attenuation relationship but we found a negative an elastic attenuation coefficient which is not correct physically. Negative value of k indicates that the assumption of a simple shape for the attenuation curve, with a constant geometrical spreading for different distances is not correct. At the closest ranges, the direct arrival dominates the waveform; but at larger ranges, the rays reflected from boundaries and all of the energy is reflected upward, so postcritical reflections become more important. The range at which the Moho reflection becomes postcritical is indicated by the abrupt increase in amplitude of that ray (Burger et al., 1987). So we performed the trilinear form of attenuation on the data (Atkinson and Mereu, 1992) to avoid the negative values of k. We used Monte Carlo technique to evaluate distance correction curves for north-westIran, and testing all possible combination that minimizes the average residual errors. Results show that we have 3 values for geometrical spreading. Apparent geometric spreading depends on the geometry of spreading in a layered crust, which is a function of distance, but anelasticity is independent of distance. These three values for geometrical spreadings are: R ≤ 85 km, n1 = 0.73; 85 >R≤ 120 km, n2 = -0.46; R>120 km, n3 = 0.22; k =0.00037 The distances less than 85 km related to direct waves. Note that distance ranges between 85 and 120 km is the distance where the Moho reflection becomes postcritical and is indicated by the abrupt increase in amplitude. The focal depth, crustal thickness, and the crustal velocity gradient have important influences on the range at which the amplitude increases. The result of ground motion in north-west Iran demonstrates that crustal structure can influence the strong motion attenuation relations. The uniform distribution of the residuals about their baselines (Fig. 4) show that the trilinear distance attenuation relation developed in this study provide more reliable estimates of ML values than those from linear relation. ML values using the linear distance attenuation are overestimated at distance larger than about 85 km (Fig. 3). We used trilinear method to estimate the local magnitude, but distance attenuation is independent from crustal structure. The attenuation along the energy ray path and the site geology conditions play roles of great importance in the recorded amplitudes. In the process of magnitude calculation, such effects are reduced if a proper attenuation function and magnitude station corrections are applied, so we applied the station correction on the amplitudes and performed a linear regression analysis on the data to obtain n and k.The results represent a logical response. No trend is evident on the distribution of residual in the corrected linear method, thus the attenuation function determined in this study does not depend on geology variation or hypocentral distances, as it works well for the north-west Iran region. The distance – correction and local magnitude function can be expressed as: -Log A0 = (1.52±0.0057) log(r/100) + (0.00137±3.20E-07) (r-100) + 3, ML = log A + (1.52 ± 0.0057) log(r/100) + (0.0013 ± 3.20E-07) (r-100) +3, The parameter k can be related to the inelastic attenuation coefficient Q using the Bakun and Joyner (1984) formula γ = ln 10k = πf/QVS, where VS is the average crustal S-wave velocity. Taking an average S wave of VS = 3.4 km /s, the k ≈ 0.00137 value obtained in the present study introduces a value of γ = k ln (10) = 0.00317 and Q(1 Hz) = 280. Nuttli (1980) found that a γ value of 0.0045 km -1 (between 0.003 and 0.006) corresponds to an apparent Q of 200 (between 152 and 303) for Sg. The γ and Q value agree with the result given by Nuttli. He showed that the attenuation of 1-sec period crustal phases in Iran is relatively high. The high attenuation value is due to the tectonic complexity and the widespread young volcanics in the region. This result should be treated with caution, because the maximum amplitude data do not necessarily correspond to a single seismic phase .

https://jesphys.ut.ac.ir/article_35595_bc432806e7528c139d8caffa4275d32f.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Deep alluvial effects on one-dimensional seismic site response in Qom city Deep alluvial effects on one-dimensional seismic site response in Qom city 15 31 35596 10.22059/jesphys.2013.35596 FA Abd-allah Sohrabi-Bidar Assistant Professor, School of Geology, University of Tehran, Iran Leila Jasempur M.Sc. Student, School of Geology, University of Tehran, Iran Journal Article 2012 11 10 *نگارنده رابط: تلفن: 61112985-021 دورنگار: 66491623-021 E-mail:sohrabi@khayam.ut.ac.ir Nowadays in many site response analyses of alluvial, environment with shear wave velocity 600 m/sec < νs < 800 m/sec is considered as the seismic bedrock. Results of these analyses did not confirm those from empirical analyses based on the recording of microtremors or weak earthquake motions. Recently, effects of deep alluviums and contrast between geologic bedrock and alluviums are considered as a possible cause for this inconformity. This study examines the site effects of deep alluviums of Qom city. Qom is located at the northern margin of central Iran zone and on the Quaternary young alluviums. Based on the geoelectrical resistivity surveys, thickness of alluviums in some parts of the city is greater than 250m. Earlier empirical studies based on the recording of microtremors had shown that at the frequencies ranging from 0.6 to 1.2 Hz, a clear amplification can be seen in the studied alluviums. Amplification at these frequencies did not confirm results from one-dimensional numerical analysis of the soft sediments on the conventional seismic bedrock. At the current study, in order to determine the geometrical properties and thickness of deep alluviums, resistivity surveys have been conducted in Qom plain was used and dynamic properties of the soil layers were determined by geological descriptions. Considering the uncertainty resulting from the lack of dynamic properties of soil layers, a parametric study was conducted and three models of low, medium and high velocity were considered for alluvial layers and bedrock. One-dimensional numerical analysis was carried out using the software Deepsoil. As the results will be compared with those from empirical analysis of small strain displacements of microtremors, a linear elastic behaviour was assumed. Amplification curves were measured using different dynamic properties of alluvial layers and the bedrock and the results were compared with those from amplification of microtremors. In all analyses conducted using different dynamical properties (three models of low, medium and high velocity), a specific amplification at the frequencies less than 1 Hz was obtained. Furthermore, amplified frequency resulted from previous empirical studies corresponds with the amplified frequency resulted from numerical analysis with high velocity model. Amplification at this frequency range and its correspondence with results of microtremors studies shows the effects of deep alluviums on the site amplification functions. The importance of deep alluviums insists on attention to the shape of the sedimentary basin and consideration of the effects of deep alluviums on the numerical site effects studies. In the case of inadequate information about the deep alluviums, it is necessary to use empirical analysis recorded motion at the site such as microtremors or weak earthquake motions. At present, consideration of site effects in most of building codes for design earthquake resistant structures are limited to effects of shallow alluviums, however, as discussed in this paper, deep alluviums are effective on site amplification specially in low frequencies and it is necessary to take them into account in the design of tall structures. *نگارنده رابط: تلفن: 61112985-021 دورنگار: 66491623-021 E-mail:sohrabi@khayam.ut.ac.ir Nowadays in many site response analyses of alluvial, environment with shear wave velocity 600 m/sec < νs < 800 m/sec is considered as the seismic bedrock. Results of these analyses did not confirm those from empirical analyses based on the recording of microtremors or weak earthquake motions. Recently, effects of deep alluviums and contrast between geologic bedrock and alluviums are considered as a possible cause for this inconformity. This study examines the site effects of deep alluviums of Qom city. Qom is located at the northern margin of central Iran zone and on the Quaternary young alluviums. Based on the geoelectrical resistivity surveys, thickness of alluviums in some parts of the city is greater than 250m. Earlier empirical studies based on the recording of microtremors had shown that at the frequencies ranging from 0.6 to 1.2 Hz, a clear amplification can be seen in the studied alluviums. Amplification at these frequencies did not confirm results from one-dimensional numerical analysis of the soft sediments on the conventional seismic bedrock. At the current study, in order to determine the geometrical properties and thickness of deep alluviums, resistivity surveys have been conducted in Qom plain was used and dynamic properties of the soil layers were determined by geological descriptions. Considering the uncertainty resulting from the lack of dynamic properties of soil layers, a parametric study was conducted and three models of low, medium and high velocity were considered for alluvial layers and bedrock. One-dimensional numerical analysis was carried out using the software Deepsoil. As the results will be compared with those from empirical analysis of small strain displacements of microtremors, a linear elastic behaviour was assumed. Amplification curves were measured using different dynamic properties of alluvial layers and the bedrock and the results were compared with those from amplification of microtremors. In all analyses conducted using different dynamical properties (three models of low, medium and high velocity), a specific amplification at the frequencies less than 1 Hz was obtained. Furthermore, amplified frequency resulted from previous empirical studies corresponds with the amplified frequency resulted from numerical analysis with high velocity model. Amplification at this frequency range and its correspondence with results of microtremors studies shows the effects of deep alluviums on the site amplification functions. The importance of deep alluviums insists on attention to the shape of the sedimentary basin and consideration of the effects of deep alluviums on the numerical site effects studies. In the case of inadequate information about the deep alluviums, it is necessary to use empirical analysis recorded motion at the site such as microtremors or weak earthquake motions. At present, consideration of site effects in most of building codes for design earthquake resistant structures are limited to effects of shallow alluviums, however, as discussed in this paper, deep alluviums are effective on site amplification specially in low frequencies and it is necessary to take them into account in the design of tall structures.

https://jesphys.ut.ac.ir/article_35596_eaf805dbf231fc7137369c8382eadb43.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Local gravity field modeling using radial basis functions, case study: coastal area of the Persian Gulf Local gravity field modeling using radial basis functions, case study: coastal area of the Persian Gulf 33 48 35597 10.22059/jesphys.2013.35597 FA Abdol-Reza Safari Associate Professor, Department of Surveying and Geomatics Engineering, University College of Engineering, University of Tehran, Iran Mohammadali Sharifi Assistant Professor, Department of Surveying and Geomatics Engineering, University College of Engineering, University of Tehran, Iran Ismaeil Foroughi M.Sc. Student of Geodesy, Department of Surveying and Geomatics Engineering, University College of Engineering, University of Tehran, Iran Journal Article 2012 12 25 *نگارنده رابط: تلفن: 66752215-021 دورنگار: 66752214-021 E-mail:e.foroughi@ut.ac.ir The determination of the earth Gravity field has various applications in geodesy and geophysics. Measuring the earth gravity field can be divided into satellite, airborne and terrestrial methods. Traditional method for gravity field modeling using these data is approximation by spherical harmonics expansion. Although spherical harmonic is one of the most popular methods to approximate gravity filed, based on their global characteristic, a small regional variation make big changes in whole spherical harmonic coefficients: Where is a point with spherical coordinate, and are normalized Legendre functions up to degree and order and are spherical harmonic coefficients. To deal with this problem, different groups of regional basis systems were introduced, as in case we can refer to gravity field modeling using radial basis functions: Where are the expansion coefficients (scale coefficients) and Bjerhammar is a sphere with radius which is entirely inside the topographic masses of the earth, are the set of radial basis functions with following representation: Where are points inside and outside of the Bjerhammar sphere respectively, is the Legendre polynomial of degree and are the Legendre coefficients, the point y is called the centre of the RBF. If locations and depths and coefficients as Radial basis function’s parameters are chosen properly we will have a good representation of potential anomaly and related earth functions. In this paper we used Levenberg Marquardt algorithm (LM) to find optimal RBF parameters, LM is a iterative regularization method, can find the best answer with following equation: Where is the Hessian matrix evaluated at , this update rule is used as follows, if the error goes down following an update, it implies that our quadratic assumption on is working well and we reduce (usually by a factor of 10) and vice versa. In this paper, we used combination of gravity data (gravity anomaly) and gravity potential data (gravity potential anomaly) derived from satellite altimetry. Significant points in this algorithm are: removing global effect of gravity anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from gravity anomaly data, using potential anomaly in test area those are calculated on Bruns formula from satellite altimetry data, removing global effect of potential anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from the previous step data, forming the observation equations with radial multipole of order 1 by residual gravity anomaly and residual potential anomaly data. Levenberg Marquardt algorithm is then used to choose optimal number and, location and depth of the radial basis functions. We also used some of potential anomaly observations as control point s in the region of coastal Persian Gulf for appraisal this algorithm and then present the gravity field in this area. *نگارنده رابط: تلفن: 66752215-021 دورنگار: 66752214-021 E-mail:e.foroughi@ut.ac.ir The determination of the earth Gravity field has various applications in geodesy and geophysics. Measuring the earth gravity field can be divided into satellite, airborne and terrestrial methods. Traditional method for gravity field modeling using these data is approximation by spherical harmonics expansion. Although spherical harmonic is one of the most popular methods to approximate gravity filed, based on their global characteristic, a small regional variation make big changes in whole spherical harmonic coefficients: Where is a point with spherical coordinate, and are normalized Legendre functions up to degree and order and are spherical harmonic coefficients. To deal with this problem, different groups of regional basis systems were introduced, as in case we can refer to gravity field modeling using radial basis functions: Where are the expansion coefficients (scale coefficients) and Bjerhammar is a sphere with radius which is entirely inside the topographic masses of the earth, are the set of radial basis functions with following representation: Where are points inside and outside of the Bjerhammar sphere respectively, is the Legendre polynomial of degree and are the Legendre coefficients, the point y is called the centre of the RBF. If locations and depths and coefficients as Radial basis function’s parameters are chosen properly we will have a good representation of potential anomaly and related earth functions. In this paper we used Levenberg Marquardt algorithm (LM) to find optimal RBF parameters, LM is a iterative regularization method, can find the best answer with following equation: Where is the Hessian matrix evaluated at , this update rule is used as follows, if the error goes down following an update, it implies that our quadratic assumption on is working well and we reduce (usually by a factor of 10) and vice versa. In this paper, we used combination of gravity data (gravity anomaly) and gravity potential data (gravity potential anomaly) derived from satellite altimetry. Significant points in this algorithm are: removing global effect of gravity anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from gravity anomaly data, using potential anomaly in test area those are calculated on Bruns formula from satellite altimetry data, removing global effect of potential anomaly by spherical harmonic up to degree and order 360 (EGM2008) and centrifugal force from the previous step data, forming the observation equations with radial multipole of order 1 by residual gravity anomaly and residual potential anomaly data. Levenberg Marquardt algorithm is then used to choose optimal number and, location and depth of the radial basis functions. We also used some of potential anomaly observations as control point s in the region of coastal Persian Gulf for appraisal this algorithm and then present the gravity field in this area.

https://jesphys.ut.ac.ir/article_35597_26ab908c1977b25326b5f19b75c97cc9.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Forward modeling of magnetic resonance sounding (MRS) for karsts and the effect of depth increase and saturation and half-saturation on inversion Forward modeling of magnetic resonance sounding (MRS) for karsts and the effect of depth increase and saturation and half-saturation on inversion 49 66 35598 10.22059/jesphys.2013.35598 FA Amin Ebrahimibardar Ph.D. Student, Earth Physics Department, Institute of Geophysics, University of Tehran, Iran Mohammad Kazem Hafizi Professor, Earth Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2010 06 29 *نگارنده رابط: تلفن: 88630477-021 دورنگار: 88630479-021 aebrahimib@ut.ac.ir E-mail: Forward modeling is regarded as the backbone of inversion methods in geophysics. Magnetic Resonance Sounding (MRS) is a rather new method in the exploration of groundwater water resources. In this method, when an E.M. field induced by Larmor frequency of water hydrogen protons the underground by a transmitter on the surface. Part of its energy is absorbed exclusively by the water molecules. When the excitation field is removed, the absorbed energy acts as a new source and it is released in the form of a new electromagnetic field which can be detected by a receiver at the surface. The response of this method is due to the presence of water in the underground layers and the basic parameters of the aquifer could also be calculated by this method. Karsts are considered as one of the most important water sources in many parts of the world. It is significant to investigate them especially in hydrology. However, the imaging of such targets is generally a difficult task for most geophysical methods. In this study, karsts are considered as complicated phenomena. Depth of karst conduit is the first important parameter and saturation of karst is the second one. They are modeled in different levels of depth in two cases of saturated and half saturated conditions. Whilst natural noise within the Larmor frequency range is generally not very large (excepting magnetic storms or other temporary disturbances). But the level of civil noise (electrical power-lines, generators, etc.) may be very high, which depends on region. The depth of investigation and resolution of the MRS method are dependent on signal to noise ratio. If the measured data are ruined by noise, it will have an adverse effect on the precision and validity of MRS results. As a result, the MRS signal has to be measured with an acceptable signal to noise ratio. We can apply different filtering methods to fulfill the best signal to noise ratio. Selection of the filtering plan depends on the noise origin. In any case study, application of the stacking is necessary. The inversion is shown in the main terms as usual, for the geophysical data, with reliance on the main issues of the plan. Data inversion is then performed and finally the effects of depth and saturation on both qualitative and quantitative data interpretation are examined. It was shown that the inversion part has a very important role and recognition of model parameters, and geology is the critical part of inversion. In this way it was shown that the interpretation of MRS Data qualitative methods for karsts appropriate response can be obtained. In addition, proficiency of filtering techniques, inversion tactics and effect of noise on MRS results are discussed. *نگارنده رابط: تلفن: 88630477-021 دورنگار: 88630479-021 aebrahimib@ut.ac.ir E-mail: Forward modeling is regarded as the backbone of inversion methods in geophysics. Magnetic Resonance Sounding (MRS) is a rather new method in the exploration of groundwater water resources. In this method, when an E.M. field induced by Larmor frequency of water hydrogen protons the underground by a transmitter on the surface. Part of its energy is absorbed exclusively by the water molecules. When the excitation field is removed, the absorbed energy acts as a new source and it is released in the form of a new electromagnetic field which can be detected by a receiver at the surface. The response of this method is due to the presence of water in the underground layers and the basic parameters of the aquifer could also be calculated by this method. Karsts are considered as one of the most important water sources in many parts of the world. It is significant to investigate them especially in hydrology. However, the imaging of such targets is generally a difficult task for most geophysical methods. In this study, karsts are considered as complicated phenomena. Depth of karst conduit is the first important parameter and saturation of karst is the second one. They are modeled in different levels of depth in two cases of saturated and half saturated conditions. Whilst natural noise within the Larmor frequency range is generally not very large (excepting magnetic storms or other temporary disturbances). But the level of civil noise (electrical power-lines, generators, etc.) may be very high, which depends on region. The depth of investigation and resolution of the MRS method are dependent on signal to noise ratio. If the measured data are ruined by noise, it will have an adverse effect on the precision and validity of MRS results. As a result, the MRS signal has to be measured with an acceptable signal to noise ratio. We can apply different filtering methods to fulfill the best signal to noise ratio. Selection of the filtering plan depends on the noise origin. In any case study, application of the stacking is necessary. The inversion is shown in the main terms as usual, for the geophysical data, with reliance on the main issues of the plan. Data inversion is then performed and finally the effects of depth and saturation on both qualitative and quantitative data interpretation are examined. It was shown that the inversion part has a very important role and recognition of model parameters, and geology is the critical part of inversion. In this way it was shown that the interpretation of MRS Data qualitative methods for karsts appropriate response can be obtained. In addition, proficiency of filtering techniques, inversion tactics and effect of noise on MRS results are discussed.

https://jesphys.ut.ac.ir/article_35598_3db629e76e59bdd62ee0dfbdfc3c5639.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Investigation of North American sector Sq-field in year 1997 using spherical harmonic analysis Investigation of North American sector Sq-field in year 1997 using spherical harmonic analysis 67 82 35599 10.22059/jesphys.2013.35599 FA Asad-allah Joata Bayrami Assistant Professor, Geophysics Department, Graduate University of Advanced Technology, Kerman, Iran Journal Article 2012 05 01 The daily record of geomagnetic variations at any world location typically shows a multitude of irregular changes in the field that represent the superposition of many spectral components whose amplitudes generally increase with increasing period. It has been a long established fact that variations in ground magnetic records are caused by the dynamo action in the upper atmosphere. These daily variations in the geomagnetic fields at the earth's surface during geomagnetically quiet conditions are known to be associated with the dynamo currents which are driven by winds and thermal tidal motions in the E-region of the ionosphere. Unique current sources in the upper atmosphere and magnetosphere have been identified as origins of many of these spectral field variations. On occasion there are days when the magnetic records smoothly change with primarily 24-, 12-, 8-, and 6-hour period spectral components dominating the field composition and few of the irregularly appearing, shorter or longer period changes are present. On these days, the oscillations of three orthogonal field components produce records that are predictably similar to others recorded many days earlier or later and follow a pattern of gradual change through the seasons of the year. Such records describe the quiet daily geomagnetic variations. When the small but persistent effects ascribed to the lunar- tidal current system have been removed, the changes are called Sq for solar quiet fields, referring to their local-time changes when solar-terrestrial disturbances are absent. Solar activity, identified with the sunspot number, controls the percentage of magnetically quiet days in a year as an inverse relationship. The quietest geomagnetic levels usually occur on, or a year after, the minimum in sunspot number. Because of the 10.6-year cycle in solar activity, a similar cycle of geomagnetically quiet years occurs. The quasilogarithmic Kp is a convenient three-hour index for selecting the quiet conditions; its linear counterpart is the Ap index. Some authors prefer to select quiet days by a limiting value of the day's Ap (e.g., Ap = 10). Others take a fixed number (e.g., five) of the quietest days (judged by the day's Ap) for a given month, whatever the values may be. The 19 North American observatories are selected in this study. There are 60 days in 1997 in which the global geomagnetic disturbance index, Kp, have all 8 daily values less than 2+. These days are taken as preliminary “quiet day” recordings. All observatories have 60-min sample records. The original recordings of field are in Universal Time (UT) as orthogonal north, east, and into-the-earth components of field as X, Y, and Z. The data for each component are Fourier analyzed for each quiet day. A systematic change in pattern of the daily variation with change in latitude is clearly evident. The large amplitude of X occurs at all observatories near the geomagnetic dip equator because of existence of the equatorial electrojet. The relation between the Chapman factor (cosχ)0.5 and Sq (Z) is investigated and concluded that the Sq (Z), corresponds in onset and subsidence with Chapman-factor change. It has been concluded that the maximum amplitudes of magnetic potentialoccur near the midlatitudes which are the locations of the external current foci. The internal Z is in the opposite direction to that of the external Z. The external and internal currents must be oppositely directed to obtain the similar pattern of X and Y but opposite pattern of Z. It seems that all three internal variation amplitudes are less than the corresponding external amplitudes. The daily record of geomagnetic variations at any world location typically shows a multitude of irregular changes in the field that represent the superposition of many spectral components whose amplitudes generally increase with increasing period. It has been a long established fact that variations in ground magnetic records are caused by the dynamo action in the upper atmosphere. These daily variations in the geomagnetic fields at the earth's surface during geomagnetically quiet conditions are known to be associated with the dynamo currents which are driven by winds and thermal tidal motions in the E-region of the ionosphere. Unique current sources in the upper atmosphere and magnetosphere have been identified as origins of many of these spectral field variations. On occasion there are days when the magnetic records smoothly change with primarily 24-, 12-, 8-, and 6-hour period spectral components dominating the field composition and few of the irregularly appearing, shorter or longer period changes are present. On these days, the oscillations of three orthogonal field components produce records that are predictably similar to others recorded many days earlier or later and follow a pattern of gradual change through the seasons of the year. Such records describe the quiet daily geomagnetic variations. When the small but persistent effects ascribed to the lunar- tidal current system have been removed, the changes are called Sq for solar quiet fields, referring to their local-time changes when solar-terrestrial disturbances are absent. Solar activity, identified with the sunspot number, controls the percentage of magnetically quiet days in a year as an inverse relationship. The quietest geomagnetic levels usually occur on, or a year after, the minimum in sunspot number. Because of the 10.6-year cycle in solar activity, a similar cycle of geomagnetically quiet years occurs. The quasilogarithmic Kp is a convenient three-hour index for selecting the quiet conditions; its linear counterpart is the Ap index. Some authors prefer to select quiet days by a limiting value of the day's Ap (e.g., Ap = 10). Others take a fixed number (e.g., five) of the quietest days (judged by the day's Ap) for a given month, whatever the values may be. The 19 North American observatories are selected in this study. There are 60 days in 1997 in which the global geomagnetic disturbance index, Kp, have all 8 daily values less than 2+. These days are taken as preliminary “quiet day” recordings. All observatories have 60-min sample records. The original recordings of field are in Universal Time (UT) as orthogonal north, east, and into-the-earth components of field as X, Y, and Z. The data for each component are Fourier analyzed for each quiet day. A systematic change in pattern of the daily variation with change in latitude is clearly evident. The large amplitude of X occurs at all observatories near the geomagnetic dip equator because of existence of the equatorial electrojet. The relation between the Chapman factor (cosχ)0.5 and Sq (Z) is investigated and concluded that the Sq (Z), corresponds in onset and subsidence with Chapman-factor change. It has been concluded that the maximum amplitudes of magnetic potentialoccur near the midlatitudes which are the locations of the external current foci. The internal Z is in the opposite direction to that of the external Z. The external and internal currents must be oppositely directed to obtain the similar pattern of X and Y but opposite pattern of Z. It seems that all three internal variation amplitudes are less than the corresponding external amplitudes.

https://jesphys.ut.ac.ir/article_35599_38e83897c73847ead4470aa98eddd28a.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Identifying and monitoring dust storm in the western part of Iran using remote sensing techniques Identifying and monitoring dust storm in the western part of Iran using remote sensing techniques 83 96 35600 10.22059/jesphys.2013.35600 FA Farahnaz Taghavi Assistant Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Elaheh Owlad M.Sc. Student of Meteorology, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Taher Safarrad M.Sc. Student of Climatology, Faculty of Geography, University of Tehran, Iran Parviz Irannejad Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2012 03 03 Mineral dust can directly affect the solar and terrestrial radiation in both visible and infrared (IR) spectral regions through scattering and absorption processes. Due to specific optical properties of dust particles, satellite observed radiances carry the spectral signatures of dust particles that are different from molecular, cloud, and underlying surface. Based on these differences, various detection schemes have been developed to distinguish dust. In practice, the detection is based on the analysis of reflectance (or radiance) in visible bands or brightness temperature (BT) in IR bands. The magnitude of the difference in BT in selected bands (or channels) can be used to infer the signature of dust. This is the essence of aerosol imagery detection algorithms (Zhao et al, 2010). Iran is located in a region that is strongly affected by dust storms. The frequency and intensity of these storms have increased in recent years. Recent studies have shown that numerical weather models alone are not able to track and detect dust storms and in many cases have significant errors (Taghavi, 2010). Remote sensing provides a valuable tool for detecting this phenomenon. In west of Iran some areas are much more prone to dust storms than others due to differing soils and climates. Even in bare deserts, the sandy areas, such as those found on the Arabian Peninsula, generally do not generate dust storms. Generally, areas with silt- and clay-rich soils are responsible for most dust storms. These storms occur when the sub-tropical jet stream migrates northward from south of the Arabian Peninsula and the polar front jet stream moves southward from the European continent (Taghavi, 2008). In this study, we enhance and survey two dust events that occurred in the west of Iran on March the 4th and April the 13th, 2011, using two different algorithms. The first algorithm uses MNDVI index and threshold temperature of 290 K in MODIS band-32 to differentiate dust from semi-arid areas with low vegetation cover and clouds, respectively. Surveys show that MNDVI index cannot clearly detect dust over water surfaces. Therefore, we use the algorithm of combining brightness temperature difference of dust between the wavelengths of 8.5μm (MODIS band-29) and 11μm (MODIS band-31) with negative values of bands-31 and 32 brightness temperature differences. For defining dust areas we use (BT8.5-BT11) – (BT11-BT12) values larger than the obtained threshold and (BT11-BT12) smaller than zero. To study the dust loading, we also use the Dust Regional Atmospheric Model (DREAM-8b). The Earth Sciences Department of Barcelona Supercomputing Center (BSC) uses the DREAM-8b model (Nickovic et al. 2001; Perez et al. 2006a, Perez et al. 2006b) to conduct modelling research and development for short-term prediction of dust. The model predicts the atmospheric life cycle of the eroded desert dust and was developed as a pluggable component of the Eta/NCEP (National Centers for Environmental Prediction) model. The recent method (using thermal infrared spectrum) detects dust well, especially over water. Comparison with quantitative aerosol optical thickness (AOT) retrieval is performed to validate the enhancement algorithms. At the end with comparing the enhanced images using IR technique with synoptic maps, MODIS AOT values, DREAM 8b model outputs and synoptic stations data, it is found that the applied enhancement algorithms provide a more reliable approach for monitoring dust storms compared to MODIS AOT retrievals or model outputs. For both dust storm cases, a low pressure was the main cause of the dust storms. Using trajectory maps, we can track the transport of dust from the main sources. Results show that for the dust storm occurred on the 4th March dust originated from the border of Iran and Iraq, then moved southward towards the Persian Gulf coasts, while that occurred on the case 13th April moved northward and approached Caspian Sea. Mineral dust can directly affect the solar and terrestrial radiation in both visible and infrared (IR) spectral regions through scattering and absorption processes. Due to specific optical properties of dust particles, satellite observed radiances carry the spectral signatures of dust particles that are different from molecular, cloud, and underlying surface. Based on these differences, various detection schemes have been developed to distinguish dust. In practice, the detection is based on the analysis of reflectance (or radiance) in visible bands or brightness temperature (BT) in IR bands. The magnitude of the difference in BT in selected bands (or channels) can be used to infer the signature of dust. This is the essence of aerosol imagery detection algorithms (Zhao et al, 2010). Iran is located in a region that is strongly affected by dust storms. The frequency and intensity of these storms have increased in recent years. Recent studies have shown that numerical weather models alone are not able to track and detect dust storms and in many cases have significant errors (Taghavi, 2010). Remote sensing provides a valuable tool for detecting this phenomenon. In west of Iran some areas are much more prone to dust storms than others due to differing soils and climates. Even in bare deserts, the sandy areas, such as those found on the Arabian Peninsula, generally do not generate dust storms. Generally, areas with silt- and clay-rich soils are responsible for most dust storms. These storms occur when the sub-tropical jet stream migrates northward from south of the Arabian Peninsula and the polar front jet stream moves southward from the European continent (Taghavi, 2008). In this study, we enhance and survey two dust events that occurred in the west of Iran on March the 4th and April the 13th, 2011, using two different algorithms. The first algorithm uses MNDVI index and threshold temperature of 290 K in MODIS band-32 to differentiate dust from semi-arid areas with low vegetation cover and clouds, respectively. Surveys show that MNDVI index cannot clearly detect dust over water surfaces. Therefore, we use the algorithm of combining brightness temperature difference of dust between the wavelengths of 8.5μm (MODIS band-29) and 11μm (MODIS band-31) with negative values of bands-31 and 32 brightness temperature differences. For defining dust areas we use (BT8.5-BT11) – (BT11-BT12) values larger than the obtained threshold and (BT11-BT12) smaller than zero. To study the dust loading, we also use the Dust Regional Atmospheric Model (DREAM-8b). The Earth Sciences Department of Barcelona Supercomputing Center (BSC) uses the DREAM-8b model (Nickovic et al. 2001; Perez et al. 2006a, Perez et al. 2006b) to conduct modelling research and development for short-term prediction of dust. The model predicts the atmospheric life cycle of the eroded desert dust and was developed as a pluggable component of the Eta/NCEP (National Centers for Environmental Prediction) model. The recent method (using thermal infrared spectrum) detects dust well, especially over water. Comparison with quantitative aerosol optical thickness (AOT) retrieval is performed to validate the enhancement algorithms. At the end with comparing the enhanced images using IR technique with synoptic maps, MODIS AOT values, DREAM 8b model outputs and synoptic stations data, it is found that the applied enhancement algorithms provide a more reliable approach for monitoring dust storms compared to MODIS AOT retrievals or model outputs. For both dust storm cases, a low pressure was the main cause of the dust storms. Using trajectory maps, we can track the transport of dust from the main sources. Results show that for the dust storm occurred on the 4th March dust originated from the border of Iran and Iraq, then moved southward towards the Persian Gulf coasts, while that occurred on the case 13th April moved northward and approached Caspian Sea.

https://jesphys.ut.ac.ir/article_35600_16a83979ebb473f455be6ecf8e1a7953.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Effect of Mediterranean systems on drought in west of Iran Effect of Mediterranean systems on drought in west of Iran 97 110 35601 10.22059/jesphys.2013.35601 FA Alireza Mohammadnejad Assistant Professor, Physics Department, University of Birjand, Iran Farhang Ahmadi-Givi Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Parviz Irannejad Assistant Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2012 04 28 The areas of the world that have Mediterranean style climate are found at about 35 degrees north and south of the equator, on the western sides of continents. The distinctive feature of this climate is the small amount of rain in the summer. Overall, the climate has a moderate amount of rainfall and warm winters and hot summers and. The climate of the Mediterranean region is conditioned by its position in the transition area between the subtropical high pressure belt and the midlatitude westerlies. In addition, the cyclones have been recognized since long as, a major meteorological feature influencing weather and climate in the Mediterranean region, often producing severe weather events. Mediterranean cyclones have also an influence on areas outside the Mediterranean region. Cyclones generated in the Mediterranean influence the weather and climate further east in Asian areaof the region to the east, including Syria, Iraq, Iran and Afghanistan. Important cyclogenesis centers of the Mediterranean consist of East and West Mediterranean, Gulf of Geneva (in North Italy), South Italy and Cyprus. In this research, effects of the Mediterranean conditions and some other large scale atmospheric factors on precipitation of Iran during 1960 to 2005 are studied. For this purpose, effect of mean sea level pressure of Mediterranean cyclogenesis centers and the positions of subtropical high pressure belt (STPB) and the Siberian high pressure on both Mediterranean cyclogenesis and precipitation in Iran are investigated. To dynamically and synoptically study the effects of these factors on precipitation in the west of Iran, sea level pressure, cyclones frequency in the cyclogenesis centers, horizontal and vertical wind, temperature and moisture fields, and temperature and moisture fluxes are analyzed. Results show that precipitation in the west of Iran depends on the mean annual surface pressure, the annual number of cyclones generated in Mediterranean centers and the position of the subtropical high pressure. In dry years, positive mean sea level pressure anomaly and negative cyclone frequency anomaly are observed in all cyclogenesise centers of Mediterranean Sea. Positive anomaly of monthly sea level pressure in cyclogenesis centers over the Mediterranean is greatest in January and gradually decreases in later months. In winter during which the west of Iran is dry, the Siberian and Azores high pressures join, and hence the cyclogenesis centers of the Mediterranean are dominated by a high pressure system. In such conditions, the Siberian high pressure is weaker and the Azores high pressure is stronger than in normal winters. In dry winters, a negative anomaly of relative and specific humidity over the Mediterranean Sea and a negative anomaly in the meridional and zonal wind in the Mediterranean Sea and over the northwest of Iran develop. This leads to a decrease flux of moisture to the west and northwest of Iran. This is consistent with what expected from dominance of Azores high pressure over the Mediterranean region in dry winters. In this situation, moisture flux from Red Sea to the south and southeast of Iran remains unaffected. The areas of the world that have Mediterranean style climate are found at about 35 degrees north and south of the equator, on the western sides of continents. The distinctive feature of this climate is the small amount of rain in the summer. Overall, the climate has a moderate amount of rainfall and warm winters and hot summers and. The climate of the Mediterranean region is conditioned by its position in the transition area between the subtropical high pressure belt and the midlatitude westerlies. In addition, the cyclones have been recognized since long as, a major meteorological feature influencing weather and climate in the Mediterranean region, often producing severe weather events. Mediterranean cyclones have also an influence on areas outside the Mediterranean region. Cyclones generated in the Mediterranean influence the weather and climate further east in Asian areaof the region to the east, including Syria, Iraq, Iran and Afghanistan. Important cyclogenesis centers of the Mediterranean consist of East and West Mediterranean, Gulf of Geneva (in North Italy), South Italy and Cyprus. In this research, effects of the Mediterranean conditions and some other large scale atmospheric factors on precipitation of Iran during 1960 to 2005 are studied. For this purpose, effect of mean sea level pressure of Mediterranean cyclogenesis centers and the positions of subtropical high pressure belt (STPB) and the Siberian high pressure on both Mediterranean cyclogenesis and precipitation in Iran are investigated. To dynamically and synoptically study the effects of these factors on precipitation in the west of Iran, sea level pressure, cyclones frequency in the cyclogenesis centers, horizontal and vertical wind, temperature and moisture fields, and temperature and moisture fluxes are analyzed. Results show that precipitation in the west of Iran depends on the mean annual surface pressure, the annual number of cyclones generated in Mediterranean centers and the position of the subtropical high pressure. In dry years, positive mean sea level pressure anomaly and negative cyclone frequency anomaly are observed in all cyclogenesise centers of Mediterranean Sea. Positive anomaly of monthly sea level pressure in cyclogenesis centers over the Mediterranean is greatest in January and gradually decreases in later months. In winter during which the west of Iran is dry, the Siberian and Azores high pressures join, and hence the cyclogenesis centers of the Mediterranean are dominated by a high pressure system. In such conditions, the Siberian high pressure is weaker and the Azores high pressure is stronger than in normal winters. In dry winters, a negative anomaly of relative and specific humidity over the Mediterranean Sea and a negative anomaly in the meridional and zonal wind in the Mediterranean Sea and over the northwest of Iran develop. This leads to a decrease flux of moisture to the west and northwest of Iran. This is consistent with what expected from dominance of Azores high pressure over the Mediterranean region in dry winters. In this situation, moisture flux from Red Sea to the south and southeast of Iran remains unaffected.

https://jesphys.ut.ac.ir/article_35601_125f751656dc595a0ea4a9adee368f35.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Detection of temperature and precipitation trends and their attribution it to the greenhouse gases (Case study: West Azerbaijan Province) Detection of temperature and precipitation trends and their attribution it to the greenhouse gases (Case study: West Azerbaijan Province) 111 128 35602 10.22059/jesphys.2013.35602 FA Alireza Massah Bavani Associate Professor, Department of Irrigation, and Drainage Engineering, Collage of Abouraihan, University of Tehran, Pakdasht, Iran Elaheh Goodarzi M.Sc. Graduate, Department of Watershed Management, Collage of Natural Resources. University of Yazd, Iran Narges Zohrabi Assistant Professor, Department of Irrigation, Science and Research Brench, Islamic Azad University, Khouzestan, Iran Saeid Lotfi Research Assistant, Water Resources Group, Water Management Office, Ministry of Energy, Tehran, Iran Journal Article 2012 05 06 Detection of changes in climate variables during the past periods and attributing them to the identified factors plays a major role in climate studies and projection of the future. Different factors can unbalance the stationary time series of a region’s climatic variables. Part of these factors are related to the interactions between the components of the Earth’s climate system which can cause internal variability in time series of climatic variables. Two important natural factors that influence climate are the Sun’s energy and volcanic eruptions. Overall changes due to natural external factors and internal climate variability in earth climate system are called natural climate variability. The increase in the carbon dioxide concentration due to human activities has been the principle factor causing warming over the past 50 years. It should be noted that the existence of a trend in the climate data of a region can not necessarily be attributed to the increase in greenhouse gases. In other words, after proving the existence of a trend in the past climate data of a region, the relationship between the trend and the increase in greenhouse gases should be proved. This study was carried out to detect the trend of temperature and precipitation of West Azerbaijan Province, Iran for the period of 1968-2008 and attributing them to the greenhouse gases. The Basin located at longitude 44º 00' to 47º 31.7' north and latitude 35º 55.2' to 39º 42' east in northwest of Iran. The Basin area is 37411/1 km2 that the thirteenth largest Province in Iran. Two approaches were used to evaluate the changes in annual series of temperature and precipitation during the period 1968-2008. The first one is based on analysis of standardized departures and the second approach is based on a multiple trend tests (Mann, 1945; Kendall, 1975). This test identifies gradual monotone rising and falling trends in a time series. On the other hand distinction between gradual trend and a rapid change is important, particularly for climate- change impacts studies. Therefore to identify temporal changes in annual precipitation and temperature series of main stations in the West Azerbaijan, we conducted multiple trends tests as suggested by McCab and Wolock (2002) by varying the beginning and ending date of the time series in 5 years steps for the period of 1968-2008. Afterward, in order to separate climate changes caused by greenhouse gases from natural variability, long-term statistics (1000 years) of temperature and precipitation, resulting from control run (fix greenhouse gases) of CGCM3 model, were used for West Azerbaijan Province. To analyze the natural variability range of two “temperature” and “precipitation” variables of the study area, first, their annual anomaly time series with respect to the average base period is calculated [By definition, temperature anomaly is the temperature difference from a base temperature, while precipitation anomaly is the precipitation ratio difference from a base precipitation, (Base period, 1971-2000)].The range of natural climate variables is determined by providing two-dimensional graphs of temperature and precipitation based on two-variant normal distribution (Von Storch and Zwiers, 2002). Finally, anomaly values of the observation stations in different regions of the case study were compared with the natural climate variability range of the region. The results show that the increase in temperature and decrease in precipitation trends are due to the climate change in 1968-2008 periods. Additionally in different parts of the studied area, the range of natural climate variables for temperature and precipitation changes is between 1.8 to -1.8°C and +40 to -40 percent, respectively. However, in the most of the regions of the West Azerbaijan Province, the last ten years of the period (1998 to 2008) have almost been located outside the range of natural climate variables. The result indicates the effect of climate changes on the climatic variables of the case study in recent years. Detection of changes in climate variables during the past periods and attributing them to the identified factors plays a major role in climate studies and projection of the future. Different factors can unbalance the stationary time series of a region’s climatic variables. Part of these factors are related to the interactions between the components of the Earth’s climate system which can cause internal variability in time series of climatic variables. Two important natural factors that influence climate are the Sun’s energy and volcanic eruptions. Overall changes due to natural external factors and internal climate variability in earth climate system are called natural climate variability. The increase in the carbon dioxide concentration due to human activities has been the principle factor causing warming over the past 50 years. It should be noted that the existence of a trend in the climate data of a region can not necessarily be attributed to the increase in greenhouse gases. In other words, after proving the existence of a trend in the past climate data of a region, the relationship between the trend and the increase in greenhouse gases should be proved. This study was carried out to detect the trend of temperature and precipitation of West Azerbaijan Province, Iran for the period of 1968-2008 and attributing them to the greenhouse gases. The Basin located at longitude 44º 00' to 47º 31.7' north and latitude 35º 55.2' to 39º 42' east in northwest of Iran. The Basin area is 37411/1 km2 that the thirteenth largest Province in Iran. Two approaches were used to evaluate the changes in annual series of temperature and precipitation during the period 1968-2008. The first one is based on analysis of standardized departures and the second approach is based on a multiple trend tests (Mann, 1945; Kendall, 1975). This test identifies gradual monotone rising and falling trends in a time series. On the other hand distinction between gradual trend and a rapid change is important, particularly for climate- change impacts studies. Therefore to identify temporal changes in annual precipitation and temperature series of main stations in the West Azerbaijan, we conducted multiple trends tests as suggested by McCab and Wolock (2002) by varying the beginning and ending date of the time series in 5 years steps for the period of 1968-2008. Afterward, in order to separate climate changes caused by greenhouse gases from natural variability, long-term statistics (1000 years) of temperature and precipitation, resulting from control run (fix greenhouse gases) of CGCM3 model, were used for West Azerbaijan Province. To analyze the natural variability range of two “temperature” and “precipitation” variables of the study area, first, their annual anomaly time series with respect to the average base period is calculated [By definition, temperature anomaly is the temperature difference from a base temperature, while precipitation anomaly is the precipitation ratio difference from a base precipitation, (Base period, 1971-2000)].The range of natural climate variables is determined by providing two-dimensional graphs of temperature and precipitation based on two-variant normal distribution (Von Storch and Zwiers, 2002). Finally, anomaly values of the observation stations in different regions of the case study were compared with the natural climate variability range of the region. The results show that the increase in temperature and decrease in precipitation trends are due to the climate change in 1968-2008 periods. Additionally in different parts of the studied area, the range of natural climate variables for temperature and precipitation changes is between 1.8 to -1.8°C and +40 to -40 percent, respectively. However, in the most of the regions of the West Azerbaijan Province, the last ten years of the period (1998 to 2008) have almost been located outside the range of natural climate variables. The result indicates the effect of climate changes on the climatic variables of the case study in recent years.

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Investigation of the effect of outflow intrusion on acoustical signal fluctuations in laboratory Investigation of the effect of outflow intrusion on acoustical signal fluctuations in laboratory 129 143 35603 10.22059/jesphys.2013.35603 FA Mohammad Aakbarinasab Ph. D. Student of Physical Oceanography Khoramshahr Marine science and Technology University, Iran Abbas Ali AliakbariBidokhti Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Masoud Sadrinasab Associate Professor, Khoramshahr Marine science and Technology University, Khoramshahr, Iran Vahid Chegini Assistant Professor, Department of Marine Engineering, Iranian National Center for Oceanography, Tehran, Iran Mohammad Mahdi Mehdizadh Assistant Professor, Physical Oceanography Hormozgan University, Iran Journal Article 2012 05 01 From the acoustical oceanography point of view the ocean is a sophisticated environment. Existence of outflow intrusion (for instance, outflow of the Persian Gulf), internal waves, and small-scale turbulence perturb the horizontally stratified character of the sound velocity and cause spatial and temporal fluctuations of the sound propagation. In this experimental study, we have investigated signals fluctuations over time (was powered by a 20 MHz/Arbitrary Waveform Generator Model DG 1022 set to generate a 10 cycle sinusoid burst at frequency of 120 kHz with amplitude of 20 volts peak-to-peak) in a pre-stratification environment outside of the intrusion of turbulent plume. All experiments were carried out in a glass tank 2.19 m long, 1.27 m wide and 0.8 m deep. Before the experiments, four transducers (of which three of them are transmitters and the rest of them as receiver) are mounted opposite to each other with a separation of 1.65 m on two iron bars inside the tank. The distance between each transducer is 0.14 m. These holders are facing each other at a distance 0.3m from the tank wall. Prior to the beginning of the experiments with stratification, the acoustic measurements were executed in fresh water. All received signals were sampled at 5 MHz in all experiments. A fourth-order Butterworth band-pass filter was applied to the received voltage time series, with cutoff frequencies at 110 and 130 kHz for the 120-kHz data. In case where a “filling box" stratification (Baines and Turner, 1969) is used, the tank was initially filled with fresh water to a depth of 0.48 m. The water was then stratified using a plume of dense salt solution falling from the end of small tube (a nozzle of 3 mm diameter) placed at 0.47 m from the base with a buoyancy flux of F=g'×Vo=. After the set-up of the “filling box" stratification in the tank (Fig 1), acoustic signals and hydrophysical data were measured simultaneously. Then to produce the outflow intrusions, a source of dyed salt solution with a density less than the previous case (“filling box") with volume flux of was entered into stratified environment. At the start of the experiment with plume intrusion the speed of the nose of the outflow increased with time. The intrusion is also thickened, and eventually split to generate a new tongue of dyed plume water growing beneath the first layer. The dye tracer in the outflow water was slowly adverted upward to replace water entrained into the plume at shallower depths, and eventually reached to the source level. The outflow intrusion is produced at the start of the experiment at the location of the transmitter in the middle of the tank (at the depth of 0.22 m). The dyed outflow water is wedged-shaped with a sloping interface beneath. In different time intervals the acoustic and hydrophysics data are measured simultaneously, and then these signals in different times, based on the place of the plume outflow, are processed. After investigating the output signals, these results are found: when the transmitter and receiver is positioned into the outflow intrusion (dyed outflow) location, the signal amplitude is decreased at different moments of plume intrusion, but if the transmitter is positioned in the upper and lower part of the outflow intrusion, it causes the signal amplitude to increase (Snell’s law). By applying trace envelope techniques on the received signals, shape of signal change was found with time. Thereby, results indicate that outflow intrusion could be important on acoustical signal fluctuations. Results indicate that outflow intrusion could be important in shapes of the received signals. Also we have observed the occurrence of major signal fluctuations over time is accordance with the sound speed vertical structure changes. It is noticed that this phenomenon is also taken place at the outflow of the Persian of Gulf to the Oman sea. The result of such simulation could be used with attention to the acoustic scale rule, (k is the wave number.) where a lab by thickness of this current at outflow of the Persian Gulf which is about <10 km. From the acoustical oceanography point of view the ocean is a sophisticated environment. Existence of outflow intrusion (for instance, outflow of the Persian Gulf), internal waves, and small-scale turbulence perturb the horizontally stratified character of the sound velocity and cause spatial and temporal fluctuations of the sound propagation. In this experimental study, we have investigated signals fluctuations over time (was powered by a 20 MHz/Arbitrary Waveform Generator Model DG 1022 set to generate a 10 cycle sinusoid burst at frequency of 120 kHz with amplitude of 20 volts peak-to-peak) in a pre-stratification environment outside of the intrusion of turbulent plume. All experiments were carried out in a glass tank 2.19 m long, 1.27 m wide and 0.8 m deep. Before the experiments, four transducers (of which three of them are transmitters and the rest of them as receiver) are mounted opposite to each other with a separation of 1.65 m on two iron bars inside the tank. The distance between each transducer is 0.14 m. These holders are facing each other at a distance 0.3m from the tank wall. Prior to the beginning of the experiments with stratification, the acoustic measurements were executed in fresh water. All received signals were sampled at 5 MHz in all experiments. A fourth-order Butterworth band-pass filter was applied to the received voltage time series, with cutoff frequencies at 110 and 130 kHz for the 120-kHz data. In case where a “filling box" stratification (Baines and Turner, 1969) is used, the tank was initially filled with fresh water to a depth of 0.48 m. The water was then stratified using a plume of dense salt solution falling from the end of small tube (a nozzle of 3 mm diameter) placed at 0.47 m from the base with a buoyancy flux of F=g'×Vo=. After the set-up of the “filling box" stratification in the tank (Fig 1), acoustic signals and hydrophysical data were measured simultaneously. Then to produce the outflow intrusions, a source of dyed salt solution with a density less than the previous case (“filling box") with volume flux of was entered into stratified environment. At the start of the experiment with plume intrusion the speed of the nose of the outflow increased with time. The intrusion is also thickened, and eventually split to generate a new tongue of dyed plume water growing beneath the first layer. The dye tracer in the outflow water was slowly adverted upward to replace water entrained into the plume at shallower depths, and eventually reached to the source level. The outflow intrusion is produced at the start of the experiment at the location of the transmitter in the middle of the tank (at the depth of 0.22 m). The dyed outflow water is wedged-shaped with a sloping interface beneath. In different time intervals the acoustic and hydrophysics data are measured simultaneously, and then these signals in different times, based on the place of the plume outflow, are processed. After investigating the output signals, these results are found: when the transmitter and receiver is positioned into the outflow intrusion (dyed outflow) location, the signal amplitude is decreased at different moments of plume intrusion, but if the transmitter is positioned in the upper and lower part of the outflow intrusion, it causes the signal amplitude to increase (Snell’s law). By applying trace envelope techniques on the received signals, shape of signal change was found with time. Thereby, results indicate that outflow intrusion could be important on acoustical signal fluctuations. Results indicate that outflow intrusion could be important in shapes of the received signals. Also we have observed the occurrence of major signal fluctuations over time is accordance with the sound speed vertical structure changes. It is noticed that this phenomenon is also taken place at the outflow of the Persian of Gulf to the Oman sea. The result of such simulation could be used with attention to the acoustic scale rule, (k is the wave number.) where a lab by thickness of this current at outflow of the Persian Gulf which is about <10 km.

https://jesphys.ut.ac.ir/article_35603_19aa0161ffe19aa9e4ccadee460f1c10.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Numerical simulation of the North Atlantic Oscillation and its impact on the South West Asia Numerical simulation of the North Atlantic Oscillation and its impact on the South West Asia 145 158 35604 10.22059/jesphys.2013.35604 FA Mohammad Ali Nasr-Esfahany Assistant Professor, Faculty of Agriculture, Shahrekord University, Iran Farhang Ahmadi-Givi Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Alireza Mohebalhojeh Associate Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2012 08 06 The impact of the North Atlantic Oscillation (NAO) on meteorological parameters in the South West Asia (SWA), especially on temperature and precipitation, is certain according to recent studies. Due to differences in methods for analyzing the effects of the two phases of NAO, however, there are differences among researchers on the details of the impact. Perhaps one reason for this inconsistency is the weakness of the impact due to the fact that the NAO occurs far upstream of the SWA. So the interaction with other stronger forcings makes it almost impossible to extract the net effects of NAO. Hence some of the previously published results are in doubt. More certain results can be obtained using numerical models when we are able to do control experiments by fixing certain desirable parameters of the atmosphere and changing the forcings of interest at the same time. In this article the general climate model ECHAM5 is employed to simulate the NAO and its impact in the SWA. Two experiments named "control experiment" (COEX) and "climatological experiment" (CLEX) are designed to verify the results previously reported by the authors in 2008. In the COES, the actual sea surface temperature (SST) and in the CLEX, the long-term mean of SST is used as an input of the model. Artificially changing the NAO index is the aim of CLEX which is done by changing the lower boundary condition of the model. For both experiments, the NAO index is computed on the basis of the method suggested by Hurrell in 1995 using sea level pressure values in the northern and subtropical regions of the North Atlantic Ocean. Then on the basis of the COEX NAO index, the critical positive and negative months of NAO are determined and the ensemble mean of some important meteorological parameters in these two groups of months are computed and analyzed. The simulation of the NAO index shows that the ECHAM5 is unable to simulate the real atmospheric values of the monthly NAO index. In particular, the positive trend of the NAO index from 1970 onwards is not predicted by ECHAM5. However this model is successful in simulation of the low-frequency variability of the NAO index. The latter findings show that the high-frequency variability of the NAO index is effectively controlled by forcings other than the SST. However it seems that the SST acts as a main forcing for low-frequency variability of the NAO index. Analysis of the ensemble mean of meteorological parameters in the critical positive and negative months shows that the patterns obtained for COEX are similar to those reported by the authors in 2008. Some small differences observed in location and magnitude of centers could be due to the differences in the type and resolution of the data. As mentioned above, the critical months are selected here on the basis of the NAO index computed for COEX. So the selected months are not critical in the CLEX. If we examine the NAO index for CLEX in the same critical months, the result is like a random distribution. Hence, no significant difference is observed between the ensemble mean of meteorological parameters in CLEX in the critical positive and negative months. Therefore, it can be concluded that the results reported by the authors in 2008 are related to the real impact of NAO in the selected months. Finally, since in the experiments carried out here only the boundary conditions and forcing functions related to the numerical representation of the atmosphere are present, it should be possible to explain the observed impact of NAO in the SWA by means of the dynamics represented by ECHAM5. The impact of the North Atlantic Oscillation (NAO) on meteorological parameters in the South West Asia (SWA), especially on temperature and precipitation, is certain according to recent studies. Due to differences in methods for analyzing the effects of the two phases of NAO, however, there are differences among researchers on the details of the impact. Perhaps one reason for this inconsistency is the weakness of the impact due to the fact that the NAO occurs far upstream of the SWA. So the interaction with other stronger forcings makes it almost impossible to extract the net effects of NAO. Hence some of the previously published results are in doubt. More certain results can be obtained using numerical models when we are able to do control experiments by fixing certain desirable parameters of the atmosphere and changing the forcings of interest at the same time. In this article the general climate model ECHAM5 is employed to simulate the NAO and its impact in the SWA. Two experiments named "control experiment" (COEX) and "climatological experiment" (CLEX) are designed to verify the results previously reported by the authors in 2008. In the COES, the actual sea surface temperature (SST) and in the CLEX, the long-term mean of SST is used as an input of the model. Artificially changing the NAO index is the aim of CLEX which is done by changing the lower boundary condition of the model. For both experiments, the NAO index is computed on the basis of the method suggested by Hurrell in 1995 using sea level pressure values in the northern and subtropical regions of the North Atlantic Ocean. Then on the basis of the COEX NAO index, the critical positive and negative months of NAO are determined and the ensemble mean of some important meteorological parameters in these two groups of months are computed and analyzed. The simulation of the NAO index shows that the ECHAM5 is unable to simulate the real atmospheric values of the monthly NAO index. In particular, the positive trend of the NAO index from 1970 onwards is not predicted by ECHAM5. However this model is successful in simulation of the low-frequency variability of the NAO index. The latter findings show that the high-frequency variability of the NAO index is effectively controlled by forcings other than the SST. However it seems that the SST acts as a main forcing for low-frequency variability of the NAO index. Analysis of the ensemble mean of meteorological parameters in the critical positive and negative months shows that the patterns obtained for COEX are similar to those reported by the authors in 2008. Some small differences observed in location and magnitude of centers could be due to the differences in the type and resolution of the data. As mentioned above, the critical months are selected here on the basis of the NAO index computed for COEX. So the selected months are not critical in the CLEX. If we examine the NAO index for CLEX in the same critical months, the result is like a random distribution. Hence, no significant difference is observed between the ensemble mean of meteorological parameters in CLEX in the critical positive and negative months. Therefore, it can be concluded that the results reported by the authors in 2008 are related to the real impact of NAO in the selected months. Finally, since in the experiments carried out here only the boundary conditions and forcing functions related to the numerical representation of the atmosphere are present, it should be possible to explain the observed impact of NAO in the SWA by means of the dynamics represented by ECHAM5.

https://jesphys.ut.ac.ir/article_35604_ba6f775d82a63b34a63f69b32f42cdee.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Preparation of atmospheric temperature and humidity isopleths maps using thermal bands of MODIS satellite images Preparation of atmospheric temperature and humidity isopleths maps using thermal bands of MODIS satellite images 159 176 35605 10.22059/jesphys.2013.35605 FA Majid Rahimzadegan Ph.D. Student, Remote Sensing Eng. Dept., KN Toosi University of Technology, Tehran, Iran Mohammad Reza Mobasheri Associate Professor, Remote Sensing Eng. Dept., KN Toosi University of Technology, Tehran, Iran Journal Article 2012 09 16 In recent years, extraction of atmospheric temperature and humidity profiles from thermal bands of satellite images is a common practice. The most deployed images for this task have been acquired by Moderate Resolution Imaging Spectroradiometer (MODIS). This sensor which is onboard of Terra and Aqua platforms consists of a spectroradiometer with 36 bands in visible (VIS), near infra-red (NIR) up to thermal infra-red (TIR) region (0.405 – 14.385 ( )). The combination of sixteen infrared spectral channels is suitable for sounding temperature and humidity profiles in the atmosphere with a relatively acceptable precision. Different daily atmospheric products of MODIS images are in access on MODIS site. Atmospheric temperature and humidity profiles are two of these products that were used in this work. These products are named MOD07 and MYD07 for Terra and Aqua platforms respectively. Other MODIS products used in this work were MOD35 and MYD35. These products are mainly used for detection of pixel cloud contamination as well as for detection of aerosol concentration in pixel. Presently, maps of temperature and humidity isopleths from MODIS images are being extracted by applying some global algorithms. In these algorithms, global profiles of temperature, moisture, and ozone are being used in the calculations, where it is believed that these algorithms are not usually valid in regional scales. It is believed that the regional algorithms can boost the precision of aforementioned maps. In this work, 5 MODIS images of 8 and 11, June 2004 and 8, 15 and 22 June 2007 and their corresponding temperature and moisture profiles were used for modeling and 4 MODIS images of June 2, 6, 7 and 21 of 2007 were used for evaluation. In order to prepare a temperature and moisture profile as an initial guess in model, a 5 year (2004–2008) radiosonde data set consisting of 240 temperature profiles all interpolated for the times of satellite overpass in June were averaged. The aforementioned radiosonde measurements were acquired from the vicinity of synoptic station. This station is located at 51o, 21’E and 35o, 41’N in the south of Tehran at an altitude of 1191 (m) from mean sea level. Also some data from other synoptic stations including Kermanshah, Tabriz, Shiraz, Ahwaz, Bandarabbass, Zahedan and Mashhad stations were used for model evaluation. A practical method for extraction of temperature from MODIS measurements is to use the predefined statistical relationship between measured or modeled radiance flux densities and the corresponding temperature and moisture profile in the atmosphere. In statistical extraction method, the regression between flux density radiated from CO2 and water vapor in corresponding absorbing bands are modeled. This method is usually used in producing the first guess profile to be used in physical models later on. A method named Localized Statistical Regression Profile Retrieval (LSRPR) for extraction of temperature profiles from MODIS images based on statistical regressions is introduced in this work. In this method an approach for improving the clear sky temperature profile calculation is presented, where using local atmospheric profiles collected by Radiosondes and corresponding MODIS images, some regression coefficient matrix is calculated locally. Then by applying this matrix to other MODIS images, one can calculate temperature profiles with a precision better than what is achieved by MODIS research team i.e. MOD07/MYD07. Here radiosonde data along with concurrent MODIS images were used and the relevant regression coefficients were calculated. The average RMSE between temperature profile calculated from LSRPR and the one measured by radiosonde in the selected stations around the country was about 3.43K. This for MODIS products was 4.66K. The average RMSE between humidity profiles calculated from LSRPR and the one measured by Radiosonde in the selected stations was 1.27 g/kg and this value for MODIS products was 1.41 g/kg. As can be seen LSRPR model shows improvement in the isopleths of temperature compared to MODIS products. This improvement for humidity isopleths was not as good as for temperature. This could be due to the low amount in humidity in June. On the other hand considerable improvements in the precision of temperature isopleths extraction can be due to the use of local temperature profiles as the first guess in extraction algorithm. Moreover the results show that in the stations other than Mehrabad airport, the RMSE between temperature and humidity profiles extracted from LSRPR algorithm and those calculated from radiosonde measurements is increased. Based on the achievements in this research, it seems that LSRPR algorithm can enhance the precision compared to MODIS and the values calculated by this method are well comparable with the radiosonde collected data. So this algorithm can be used as an efficient method in regions such as Iran with relatively low number of radiosonde stations and irregular radiosonde measurements for producing temperature and humidity isopleths maps at different pressure levels in the atmosphere. It is hoped that by using these maps the accuracy of weather and climate prediction in the regional scale can be increased. In recent years, extraction of atmospheric temperature and humidity profiles from thermal bands of satellite images is a common practice. The most deployed images for this task have been acquired by Moderate Resolution Imaging Spectroradiometer (MODIS). This sensor which is onboard of Terra and Aqua platforms consists of a spectroradiometer with 36 bands in visible (VIS), near infra-red (NIR) up to thermal infra-red (TIR) region (0.405 – 14.385 ( )). The combination of sixteen infrared spectral channels is suitable for sounding temperature and humidity profiles in the atmosphere with a relatively acceptable precision. Different daily atmospheric products of MODIS images are in access on MODIS site. Atmospheric temperature and humidity profiles are two of these products that were used in this work. These products are named MOD07 and MYD07 for Terra and Aqua platforms respectively. Other MODIS products used in this work were MOD35 and MYD35. These products are mainly used for detection of pixel cloud contamination as well as for detection of aerosol concentration in pixel. Presently, maps of temperature and humidity isopleths from MODIS images are being extracted by applying some global algorithms. In these algorithms, global profiles of temperature, moisture, and ozone are being used in the calculations, where it is believed that these algorithms are not usually valid in regional scales. It is believed that the regional algorithms can boost the precision of aforementioned maps. In this work, 5 MODIS images of 8 and 11, June 2004 and 8, 15 and 22 June 2007 and their corresponding temperature and moisture profiles were used for modeling and 4 MODIS images of June 2, 6, 7 and 21 of 2007 were used for evaluation. In order to prepare a temperature and moisture profile as an initial guess in model, a 5 year (2004–2008) radiosonde data set consisting of 240 temperature profiles all interpolated for the times of satellite overpass in June were averaged. The aforementioned radiosonde measurements were acquired from the vicinity of synoptic station. This station is located at 51o, 21’E and 35o, 41’N in the south of Tehran at an altitude of 1191 (m) from mean sea level. Also some data from other synoptic stations including Kermanshah, Tabriz, Shiraz, Ahwaz, Bandarabbass, Zahedan and Mashhad stations were used for model evaluation. A practical method for extraction of temperature from MODIS measurements is to use the predefined statistical relationship between measured or modeled radiance flux densities and the corresponding temperature and moisture profile in the atmosphere. In statistical extraction method, the regression between flux density radiated from CO2 and water vapor in corresponding absorbing bands are modeled. This method is usually used in producing the first guess profile to be used in physical models later on. A method named Localized Statistical Regression Profile Retrieval (LSRPR) for extraction of temperature profiles from MODIS images based on statistical regressions is introduced in this work. In this method an approach for improving the clear sky temperature profile calculation is presented, where using local atmospheric profiles collected by Radiosondes and corresponding MODIS images, some regression coefficient matrix is calculated locally. Then by applying this matrix to other MODIS images, one can calculate temperature profiles with a precision better than what is achieved by MODIS research team i.e. MOD07/MYD07. Here radiosonde data along with concurrent MODIS images were used and the relevant regression coefficients were calculated. The average RMSE between temperature profile calculated from LSRPR and the one measured by radiosonde in the selected stations around the country was about 3.43K. This for MODIS products was 4.66K. The average RMSE between humidity profiles calculated from LSRPR and the one measured by Radiosonde in the selected stations was 1.27 g/kg and this value for MODIS products was 1.41 g/kg. As can be seen LSRPR model shows improvement in the isopleths of temperature compared to MODIS products. This improvement for humidity isopleths was not as good as for temperature. This could be due to the low amount in humidity in June. On the other hand considerable improvements in the precision of temperature isopleths extraction can be due to the use of local temperature profiles as the first guess in extraction algorithm. Moreover the results show that in the stations other than Mehrabad airport, the RMSE between temperature and humidity profiles extracted from LSRPR algorithm and those calculated from radiosonde measurements is increased. Based on the achievements in this research, it seems that LSRPR algorithm can enhance the precision compared to MODIS and the values calculated by this method are well comparable with the radiosonde collected data. So this algorithm can be used as an efficient method in regions such as Iran with relatively low number of radiosonde stations and irregular radiosonde measurements for producing temperature and humidity isopleths maps at different pressure levels in the atmosphere. It is hoped that by using these maps the accuracy of weather and climate prediction in the regional scale can be increased.

https://jesphys.ut.ac.ir/article_35605_5c156acce8f711219e39c29b1e1f601e.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Application of ordinary and complex methods for filling random gaps in total ozone data Application of ordinary and complex methods for filling random gaps in total ozone data 177 189 35606 10.22059/jesphys.2013.35606 FA Maryam Gharaylou Assistant Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Nafiseh Pegahfar Assistant Professor, Iranian National Institute for Oceanography and Atmospheric Science, Tehran, Iran Majid Mazraeh Farahani Assistant Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2012 11 10 Ozone gas has a major controlling factor for solar radiation of the shortest wavelength that reaches the earth surface. This gas is formed by chemical reaction and its formation process has been considered in various researches. Ozone is closely related to sun radiation time, relative air humidity and temperature. So ozone gas has been investigated from various interests. But one of remarkable problems challenge scientists is missing data or even unmeasured data in some periods. Hence suggesting a technique to solve this problem has a high degree of importance. Therefore, the main aim of this paper was formed. In this study, six years observed data (2005-2010) of total ozone measured both by Dobson and TOMS satellite were used. Dobson spectrophotometer (D109) has been installed at the Institute of Geophysics of University of Tehran. This institute situated in the north of Tehran with geographical characteristics of 35.44 oN and 51.23 oE and elevation of 1418.6 m above sea level. The correlation coefficient between the observational Dobson and measured satellite data has been calculated. The results show that the maximum value of the determination coefficient occurred in spring, winter, autumn and summer, respectively. Also the minimum value of the determination coefficient (R2=0.0596) happened in autumn of the year of 2005, while the maximum value of this coefficient (R2=0.9623) computed in autumn of the year of 2010. Following to investigate the accuracy of each ordinary interpolation methods to fill total ozone data gaps, some interpolation methods were selected. These methods includes Nearest, Linear, Spline and Pchip. Data investigation showed that frequent gaps last 1, 2, 3, 4 and 5 days. To clarify the accuracy of each method, first randomly missing periods were produced with the same length. Then to evaluate the performance of the four interpolation methods, Index of Agreement (IOA) was computed. In this evaluation method, the predicted values are compared with the measured values. Values of IOA greater than 0.5 indicate that the applied method for predicting performs well (Willmott 1981). In this paper, values of IOA were calculated using the results of interpolation methods and the original observed data for each period. The present paper indicates that the Spline method produces the more acceptable IOA, but this method creates least accuracy in estimating missed data, compare with other methods. It is also worthwhile to note that other interpolation methods produced similar IOA. In second step, the operation of a complex method, namely wavelet transform, for filling real gaps was studied. It should be noted that the wavelet transform has also been used in other meteorological fields such as the time series analysis of soil changes, the relationship between rainfall and runoff, simulations of photochemical reactions, mountain waves, ENSO and predicting floods and droughts. For this aim, missed data in signal of total ozone data for 2009 were constructed using wavelet theory. The outcomes of applying this theory to the observed data were compared with satellite data at the same time. The results showed that the reconstructed signal and the signal measured by satellite were consistent. Ozone gas has a major controlling factor for solar radiation of the shortest wavelength that reaches the earth surface. This gas is formed by chemical reaction and its formation process has been considered in various researches. Ozone is closely related to sun radiation time, relative air humidity and temperature. So ozone gas has been investigated from various interests. But one of remarkable problems challenge scientists is missing data or even unmeasured data in some periods. Hence suggesting a technique to solve this problem has a high degree of importance. Therefore, the main aim of this paper was formed. In this study, six years observed data (2005-2010) of total ozone measured both by Dobson and TOMS satellite were used. Dobson spectrophotometer (D109) has been installed at the Institute of Geophysics of University of Tehran. This institute situated in the north of Tehran with geographical characteristics of 35.44 oN and 51.23 oE and elevation of 1418.6 m above sea level. The correlation coefficient between the observational Dobson and measured satellite data has been calculated. The results show that the maximum value of the determination coefficient occurred in spring, winter, autumn and summer, respectively. Also the minimum value of the determination coefficient (R2=0.0596) happened in autumn of the year of 2005, while the maximum value of this coefficient (R2=0.9623) computed in autumn of the year of 2010. Following to investigate the accuracy of each ordinary interpolation methods to fill total ozone data gaps, some interpolation methods were selected. These methods includes Nearest, Linear, Spline and Pchip. Data investigation showed that frequent gaps last 1, 2, 3, 4 and 5 days. To clarify the accuracy of each method, first randomly missing periods were produced with the same length. Then to evaluate the performance of the four interpolation methods, Index of Agreement (IOA) was computed. In this evaluation method, the predicted values are compared with the measured values. Values of IOA greater than 0.5 indicate that the applied method for predicting performs well (Willmott 1981). In this paper, values of IOA were calculated using the results of interpolation methods and the original observed data for each period. The present paper indicates that the Spline method produces the more acceptable IOA, but this method creates least accuracy in estimating missed data, compare with other methods. It is also worthwhile to note that other interpolation methods produced similar IOA. In second step, the operation of a complex method, namely wavelet transform, for filling real gaps was studied. It should be noted that the wavelet transform has also been used in other meteorological fields such as the time series analysis of soil changes, the relationship between rainfall and runoff, simulations of photochemical reactions, mountain waves, ENSO and predicting floods and droughts. For this aim, missed data in signal of total ozone data for 2009 were constructed using wavelet theory. The outcomes of applying this theory to the observed data were compared with satellite data at the same time. The results showed that the reconstructed signal and the signal measured by satellite were consistent.

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Investigation of surface ozone over Tehran for 2008-2011 Investigation of surface ozone over Tehran for 2008-2011 191 206 35607 10.22059/jesphys.2013.35607 FA Zahra Shariepour Research Assistant, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Abbas Ali Aliakbari Bidokhti Professor, Space Physics Department, Institute of Geophysics, University of Tehran, Iran Journal Article 2013 02 18 Near surface ozone in urban areas can be potentially hazardous for the city dwellers. As a secondary pollutant it can also be an indicator for other air pollutants as nitrogen oxides, NOx and phenol acetate nitrate (PAN). In this paper time and spatial variations of near surface ozone and the effective meteorological parameters influencing it concentrations, have been investigated for Tehran for the period 2008-2011. The hourly ozone data of four stations namely Aghdasieh (north east), Geophysics (central), Poonak (north west) and Ray (south) for this period were acquired from the Air Quality Control company of Tehran, and the hourly temperature difference between the near surface and 8 m height were also from the Resalat Mast west of the city. The meteorological data were acquired from the Geophysics station and the data of the vertical distributions of humidity were from Wyoming University data base that provides Skew-T data of the troposphere. The synoptic maps were also acquired from NOAA. Ozone air pollution index for some air pollution stations as Aghdasieh (north east of the city) show that the period with highest concentration during the year are warm summer months in which 93% of the days were unhealthy. The daily peak of ozone concentration is found at 15-17 hours local time, depending on various meteorological parameters especially air temperature and solar radiation. There is also a strong correlation between the ozone concentration at 11AM local time and its daily mean. Usually the mean daily ozone concentration is about 66% of that of the values at 11AM local time. The annual peak of the ozone concentration is also in summer as expected. It is also found that as the nocturnal temperature inversion in the surface layer is reduced or the overall stability of the atmosphere is reduced the near surface concentration of ozone increased. This is attributed to the easier down mixing of the ozone in the residual layer (formed previous day) towards the surface. Tehran is surrounded by high mountains in the north and to some extent in the east affecting local near surface circulation. Such flows may advect air with different air pollutants especially from the emission areas (mainly center and south of the city) towards north or east, as towards Agdasieh, the station with an ozone monitoring facility. Spring time surface ozone variations also show that some mid-latitude low pressure weather system can cause strong tropospheric mixing, including tropopause folding, hence down transport of stratospheric ozone rich air towards the surface. While meteorological conditions associated with maxima of near surface ozone in summers are those with anticyclonic systems in the mid-troposphere of this area. Such conditions are associated with clear skies and strong solar radiations leading to strong photochemical activities that are essential for ozone formation in the atmosphere. It is also found that precipitation strongly reduces the air pollutants including ozone. It is interesting that following such perceptive events as the sky clears, ozone rate of concentration increase is faster than those of other pollutants. More clear sky following such events leads to stronger solar radiation near the earth surface, leading to stronger built up of ozone near surface. Near surface ozone in urban areas can be potentially hazardous for the city dwellers. As a secondary pollutant it can also be an indicator for other air pollutants as nitrogen oxides, NOx and phenol acetate nitrate (PAN). In this paper time and spatial variations of near surface ozone and the effective meteorological parameters influencing it concentrations, have been investigated for Tehran for the period 2008-2011. The hourly ozone data of four stations namely Aghdasieh (north east), Geophysics (central), Poonak (north west) and Ray (south) for this period were acquired from the Air Quality Control company of Tehran, and the hourly temperature difference between the near surface and 8 m height were also from the Resalat Mast west of the city. The meteorological data were acquired from the Geophysics station and the data of the vertical distributions of humidity were from Wyoming University data base that provides Skew-T data of the troposphere. The synoptic maps were also acquired from NOAA. Ozone air pollution index for some air pollution stations as Aghdasieh (north east of the city) show that the period with highest concentration during the year are warm summer months in which 93% of the days were unhealthy. The daily peak of ozone concentration is found at 15-17 hours local time, depending on various meteorological parameters especially air temperature and solar radiation. There is also a strong correlation between the ozone concentration at 11AM local time and its daily mean. Usually the mean daily ozone concentration is about 66% of that of the values at 11AM local time. The annual peak of the ozone concentration is also in summer as expected. It is also found that as the nocturnal temperature inversion in the surface layer is reduced or the overall stability of the atmosphere is reduced the near surface concentration of ozone increased. This is attributed to the easier down mixing of the ozone in the residual layer (formed previous day) towards the surface. Tehran is surrounded by high mountains in the north and to some extent in the east affecting local near surface circulation. Such flows may advect air with different air pollutants especially from the emission areas (mainly center and south of the city) towards north or east, as towards Agdasieh, the station with an ozone monitoring facility. Spring time surface ozone variations also show that some mid-latitude low pressure weather system can cause strong tropospheric mixing, including tropopause folding, hence down transport of stratospheric ozone rich air towards the surface. While meteorological conditions associated with maxima of near surface ozone in summers are those with anticyclonic systems in the mid-troposphere of this area. Such conditions are associated with clear skies and strong solar radiations leading to strong photochemical activities that are essential for ozone formation in the atmosphere. It is also found that precipitation strongly reduces the air pollutants including ozone. It is interesting that following such perceptive events as the sky clears, ozone rate of concentration increase is faster than those of other pollutants. More clear sky following such events leads to stronger solar radiation near the earth surface, leading to stronger built up of ozone near surface.

https://jesphys.ut.ac.ir/article_35607_a9f73fe711106b2866223248cfbbe27d.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 Application of improved local phase filter for edge detection of magnetic anomalies, A case study: Tighe Now Ab iron deposit (Byrjand) Application of improved local phase filter for edge detection of magnetic anomalies, A case study: Tighe Now Ab iron deposit (Byrjand) 207 219 35608 10.22059/jesphys.2013.35608 FA Moslem Fatehi Ph.D. Student of Mining Engineering – Exploration, Faculty of Mining Engineering, University of Isfahan, Iran Gholam Hossein Norouzi Associate Professor of Mining Engineering, Faculty of Mining Engineering, University of Tehran, Iran Meysam Abedi Ph.D. Student, Faculty of Mining Engineering – Exploration, University of Tehran, Iran Journal Article 2011 07 06 Magnetic survey is nowadays the most efficient non-destructive geophysical method. This technique puts emphasis on the measurement of anomalies of the Earth’s magnetic field, caused by the presence of archaeological remains in the ground. Magnetic survey is one of the oldest geophysical methods for airborne and land use. That is why there is a large volume of data that could be used for geological studies and deposits exploration. In this method, the intensity of earth's magnetic field is measured. The method is used for metal objects exploration in archeology, engineering investigations, metal mineral exploration, oil and gas exploration, as well as the regional geological studies for the study of igneous basement. The magnetic techniques in mineral exploration are used for both of the magnetic minerals and non-magnetic minerals exploration associated with magnetic ones. Magnetic and gravity surveys are usually based on potential field methods. In potential field data processing the edge enhancement is an important issue. Edge enhancement of potential field data has been widely used as a tool in mineral exploration prospects. Vertical derivatives of potential field data are in current approach to enhance observed probable anomalies. A well-known method of enhancing boundaries of underground structures corresponds to the zero contour of the second vertical derivative of gravity or reduced-to-the-pole of magnetic fields. However, as is well known, the estimated boundaries acquired by such technique are systematically shifted from the true position even for vertical-sided sources, and application of this method produces fairly complicated results in multi-source cases (Fedi and Florio, 2001). Cordell and Grauch (1985) also showed that the maximum of horizontal derivative is applied to the gravity or pseudo gravity anomalies localized above abrupt changes of density or magnetization. Potential field data often contains anomalies with a wide range of amplitude, and while the weak anomalies may be considered as useful geological phenomenas, they can be difficult to recognize among the strong anomalies in the total horizontal derivative (THD) method (Ma, 2013). The other complexity in potential field data is the effect of adjacent anomalies. The THD method is not successful to enhance the boundary of these models. Analytic signal (Nabighian, 1972, 1974) is another method for processing and interpretation of magnetic field data. Analytical signal is combination of vertical and horizontal derivatives of magnetic field that can also be used to determine the location of the masses. The high values in this map indicate the location of the masses. Recently, numerous edge-detection filters have been used which are based on the horizontal and vertical derivatives of potential field data and they display a balanced result. Miller and Singh (1994) proposed using the tilt angle to enhance the edges of the sources. Tilt angle is an effective method in balancing the amplitude of strong and weak anomalies, but it is not exactly an edge detection filter. Wijns et al. (2005) introduced the theta map as an edge detection method that uses the amplitude of analytic signal relative to the total horizontal derivative. The maximum of the theta map are located over the edges of causative sources. The theta map displays the edges of the shallow and deep bodies simultaneously, but the edges of the sources are diffused. In order to increase the resolution of theta map filter, Ma (2013) proposed second order of the theta map (STM). He also suggested a high resolution filter to enhance the edges of potential field data (improved local phase (ILP)), which consists of first order and second order horizontal derivatives. In this paper we use and compare phase based methods (such as tilt angle and theta map) and improved local phase filters in magnetic data interpretation. To evaluate the capability of the methods, magnetic anomalies caused by synthetic bodies are examined. After acquiring satisfactory results, these techniques are applied on real data. Ultimately, magnetic anomaly of iron ore body belonged to Tighe Now Ab iron deposit located in the north-east of Iran is used. As a consequence, drilling borehole results are incorporated to validate the outcomes. Magnetic survey is nowadays the most efficient non-destructive geophysical method. This technique puts emphasis on the measurement of anomalies of the Earth’s magnetic field, caused by the presence of archaeological remains in the ground. Magnetic survey is one of the oldest geophysical methods for airborne and land use. That is why there is a large volume of data that could be used for geological studies and deposits exploration. In this method, the intensity of earth's magnetic field is measured. The method is used for metal objects exploration in archeology, engineering investigations, metal mineral exploration, oil and gas exploration, as well as the regional geological studies for the study of igneous basement. The magnetic techniques in mineral exploration are used for both of the magnetic minerals and non-magnetic minerals exploration associated with magnetic ones. Magnetic and gravity surveys are usually based on potential field methods. In potential field data processing the edge enhancement is an important issue. Edge enhancement of potential field data has been widely used as a tool in mineral exploration prospects. Vertical derivatives of potential field data are in current approach to enhance observed probable anomalies. A well-known method of enhancing boundaries of underground structures corresponds to the zero contour of the second vertical derivative of gravity or reduced-to-the-pole of magnetic fields. However, as is well known, the estimated boundaries acquired by such technique are systematically shifted from the true position even for vertical-sided sources, and application of this method produces fairly complicated results in multi-source cases (Fedi and Florio, 2001). Cordell and Grauch (1985) also showed that the maximum of horizontal derivative is applied to the gravity or pseudo gravity anomalies localized above abrupt changes of density or magnetization. Potential field data often contains anomalies with a wide range of amplitude, and while the weak anomalies may be considered as useful geological phenomenas, they can be difficult to recognize among the strong anomalies in the total horizontal derivative (THD) method (Ma, 2013). The other complexity in potential field data is the effect of adjacent anomalies. The THD method is not successful to enhance the boundary of these models. Analytic signal (Nabighian, 1972, 1974) is another method for processing and interpretation of magnetic field data. Analytical signal is combination of vertical and horizontal derivatives of magnetic field that can also be used to determine the location of the masses. The high values in this map indicate the location of the masses. Recently, numerous edge-detection filters have been used which are based on the horizontal and vertical derivatives of potential field data and they display a balanced result. Miller and Singh (1994) proposed using the tilt angle to enhance the edges of the sources. Tilt angle is an effective method in balancing the amplitude of strong and weak anomalies, but it is not exactly an edge detection filter. Wijns et al. (2005) introduced the theta map as an edge detection method that uses the amplitude of analytic signal relative to the total horizontal derivative. The maximum of the theta map are located over the edges of causative sources. The theta map displays the edges of the shallow and deep bodies simultaneously, but the edges of the sources are diffused. In order to increase the resolution of theta map filter, Ma (2013) proposed second order of the theta map (STM). He also suggested a high resolution filter to enhance the edges of potential field data (improved local phase (ILP)), which consists of first order and second order horizontal derivatives. In this paper we use and compare phase based methods (such as tilt angle and theta map) and improved local phase filters in magnetic data interpretation. To evaluate the capability of the methods, magnetic anomalies caused by synthetic bodies are examined. After acquiring satisfactory results, these techniques are applied on real data. Ultimately, magnetic anomaly of iron ore body belonged to Tighe Now Ab iron deposit located in the north-east of Iran is used. As a consequence, drilling borehole results are incorporated to validate the outcomes.

https://jesphys.ut.ac.ir/article_35608_b16f9c3d27a2729b028a2f5dbe4b3fc8.pdf

University of Tehran Press Journal of the Earth and Space Physics 2538-371X 39 3 2013 10 23 The improvement of reduced-dynamic orbit of LEO satellites using best-fitting reference orbit The improvement of reduced-dynamic orbit of LEO satellites using best-fitting reference orbit 221 232 35609 10.22059/jesphys.2013.35609 FA Mohammad Reza Seif Ph.D. Student of Geodesy, Department of Surveying and Geomatic Engineering, University of Tehran, Iran Mohammad Ali Sharifi Assistant Professor, Department of Surveying and Geomatic Engineering, University of Tehran, Iran Masoud Abbas Hadi Graduate Student of Geodesy, Department of Surveying and Geomatics Engineering, University of Tehran, Iran Journal Article 2011 09 07 Satellite orbit determination is a method of determining the state vector, i.e., position and velocity, of a Low Earth Orbiting (LEO) satellite or interplanetary spacecraft. During the past two decades, many satellites with various applications including geodetic applications have been launched at low altitudes. For instance, TOPEX / POSEIDON, CHAMP, GRACE and GOCE are the examples of the geodetic LEO satellites. They are dominantly affected by the disturbances forces, i.e., the Earth’s gravity field anomalies and the atmospheric drag. Therefore, the LEO satellites orbit determination has special complexity and challenges which needs particular consideration. In many researches, three techniques namely dynamic, kinematic and reduced dynamics approaches are implemented for LEO satellite orbit determination. In the dynamic approach, the satellite’s motion is modeled by the equation of motion which is expressed in the Earth Centered Inertial (ECI) frame. In this method, all forces acting on a satellite are computed using the dynamical model and numerically integrated to propagate the state vector to the subsequent epochs from an initial state vector. The dynamic model describing the satellite motion with time is constructed using the forces acting on the satellite. The gravitational forces such as the Earth and the Sun and Moon and any other third body gravitational attraction and their indirect effect and non-gravitational forces such as atmospheric drag and solar radiation pressure have been modeled for orbit determination procedure. Kinematic orbit determination is a purely geometrical approach based on the observations that requires neither dynamic force models nor the physical information. The kinematic orbit is derived from observations. In the classical implementation of this approach, the orbital elements are derived from angular observations, e.g., azimuth and elevation of satellite. Nowadays, Global Navigation Satellite Systems (GNSS) especially Global Positioning System (GPS) could represent independent continuous kinematic orbit. The kinematic orbit derived from GPS observations is a dense and accurate orbit. It provides necessary information for many applications in satellite geodesy. However, the accuracy of kinematic orbit is limited to noise, systematic and gross errors of observations. The mismodeling of dynamic orbit and GPS measurement errors of kinematic orbit are both reduced when dynamic and geometrical information is combined in the reduced-dynamic orbit. The reduced dynamic orbit is generated by incorporating dynamic models as the dynamic model of the dynamic system of the orbital motion with the kinematic orbit in dynamic filtering process. Using the dynamic model, the effects of observation errors, noise, systematic and gross errors, will be reduced. Kalman filtering is the most widely used method in satellite reduced-dynamic orbit determination process. It is useable for linear dynamic system with linear observation equations. However, the Extended Kalman Filter (EKF) or the linearized form the system equations should be used. In the case of linear form application, the initial value of unknowns is required. The problem of orbit determination is one the highly nonlinear problem in engineering applications. For the implementation of the standard form of the Kalman filter for orbit determination, the initial orbit has to be computed. Different orbit determination methods are introduced for this purpose. In this article the idea of reference orbit determination based on the numerical integration is introduced. The reference orbit is an initial approximation of the observed satellite orbit that can be used for linearizing purposes. The reference orbit is determined using numerical integration methods. It deviates from the real orbit because of using erroneous initial values and difference in the Earth’s real and reference gravitational field. Consequently, the reference positions of satellites, derived from the reference orbit, are different from the actual positions. The differences in positions are called the location errors. In order to minimize the location errors, the reference orbit should be computed as close as possible to the real orbit. In this paper, the least squares approach is proposed for selecting the initial conditions in a way that the total misfit of the reference orbit and to the observed orbit is minimized. When integrating a reference orbit in a time interval, the location error is zero at the initial time and it increases linearly to a maximum at the end of time interval or the so-called the v-shaped pattern of the error. It may be better to uniformly distribute the differences over the interval. In other words, the v-shaped pattern of the differences is changed in such a way that the deviation of two orbits remains constant. This orbit is called the best-fitting reference orbit. The more accurate reference orbit the less linearization error occurs. By using the best-fitting reference orbit instead of initial one in Kalman filter algorithm, 3D RMS of reduced-dynamic orbit is reduced to 1 meter over a full day. Satellite orbit determination is a method of determining the state vector, i.e., position and velocity, of a Low Earth Orbiting (LEO) satellite or interplanetary spacecraft. During the past two decades, many satellites with various applications including geodetic applications have been launched at low altitudes. For instance, TOPEX / POSEIDON, CHAMP, GRACE and GOCE are the examples of the geodetic LEO satellites. They are dominantly affected by the disturbances forces, i.e., the Earth’s gravity field anomalies and the atmospheric drag. Therefore, the LEO satellites orbit determination has special complexity and challenges which needs particular consideration. In many researches, three techniques namely dynamic, kinematic and reduced dynamics approaches are implemented for LEO satellite orbit determination. In the dynamic approach, the satellite’s motion is modeled by the equation of motion which is expressed in the Earth Centered Inertial (ECI) frame. In this method, all forces acting on a satellite are computed using the dynamical model and numerically integrated to propagate the state vector to the subsequent epochs from an initial state vector. The dynamic model describing the satellite motion with time is constructed using the forces acting on the satellite. The gravitational forces such as the Earth and the Sun and Moon and any other third body gravitational attraction and their indirect effect and non-gravitational forces such as atmospheric drag and solar radiation pressure have been modeled for orbit determination procedure. Kinematic orbit determination is a purely geometrical approach based on the observations that requires neither dynamic force models nor the physical information. The kinematic orbit is derived from observations. In the classical implementation of this approach, the orbital elements are derived from angular observations, e.g., azimuth and elevation of satellite. Nowadays, Global Navigation Satellite Systems (GNSS) especially Global Positioning System (GPS) could represent independent continuous kinematic orbit. The kinematic orbit derived from GPS observations is a dense and accurate orbit. It provides necessary information for many applications in satellite geodesy. However, the accuracy of kinematic orbit is limited to noise, systematic and gross errors of observations. The mismodeling of dynamic orbit and GPS measurement errors of kinematic orbit are both reduced when dynamic and geometrical information is combined in the reduced-dynamic orbit. The reduced dynamic orbit is generated by incorporating dynamic models as the dynamic model of the dynamic system of the orbital motion with the kinematic orbit in dynamic filtering process. Using the dynamic model, the effects of observation errors, noise, systematic and gross errors, will be reduced. Kalman filtering is the most widely used method in satellite reduced-dynamic orbit determination process. It is useable for linear dynamic system with linear observation equations. However, the Extended Kalman Filter (EKF) or the linearized form the system equations should be used. In the case of linear form application, the initial value of unknowns is required. The problem of orbit determination is one the highly nonlinear problem in engineering applications. For the implementation of the standard form of the Kalman filter for orbit determination, the initial orbit has to be computed. Different orbit determination methods are introduced for this purpose. In this article the idea of reference orbit determination based on the numerical integration is introduced. The reference orbit is an initial approximation of the observed satellite orbit that can be used for linearizing purposes. The reference orbit is determined using numerical integration methods. It deviates from the real orbit because of using erroneous initial values and difference in the Earth’s real and reference gravitational field. Consequently, the reference positions of satellites, derived from the reference orbit, are different from the actual positions. The differences in positions are called the location errors. In order to minimize the location errors, the reference orbit should be computed as close as possible to the real orbit. In this paper, the least squares approach is proposed for selecting the initial conditions in a way that the total misfit of the reference orbit and to the observed orbit is minimized. When integrating a reference orbit in a time interval, the location error is zero at the initial time and it increases linearly to a maximum at the end of time interval or the so-called the v-shaped pattern of the error. It may be better to uniformly distribute the differences over the interval. In other words, the v-shaped pattern of the differences is changed in such a way that the deviation of two orbits remains constant. This orbit is called the best-fitting reference orbit. The more accurate reference orbit the less linearization error occurs. By using the best-fitting reference orbit instead of initial one in Kalman filter algorithm, 3D RMS of reduced-dynamic orbit is reduced to 1 meter over a full day.

https://jesphys.ut.ac.ir/article_35609_c258f8159f75b82a4e22e269c2c427e9.pdf