عنوان مقاله [English]
Changing altimetry information from satellites on the surface of seas and oceans, into anomaly gravity for example free air anomaly, is a fundamentally new method presented by researches. The determination of the free air gravity anomaly over the Earth’s marine regions has led to a major improvement in our understanding of plate tectonic processes relating to oceanic ridges, the formation of marine sediment. In recent years satellite altimetry has emerged as a powerful reconnaissance tool for exploration of sedimentary basins on continental margins as well as in deep-water regions. With the advent of more altimetric missions, with increasing accuracies and varying orbital configurations, it has become possible to generate large-scale altimeter-derived residual geoid and gravity anomaly maps over the oceans. Satellite altimetry is one of the most accurate and unique techniques ever known. Applying this technique, we are able to dominate much surface observation compared with parallel techniques. Measuring the topography of the sea surface and possible changes during time interval, the due altimeters provide us with useful information about gravity field, form and structure of the seabed, heat conditions, salinity and oceanic currents.
Through satellite altimetry observations and known coordinates on Mean Sea Level (MSL), we can measure the differential gravity potential between reference Ellipsoid and mean sea level by reversing Bruns formula. Obtaining the potential of geoid, we can estimate the ellipsoidal potential. Then through Abel-Poisson's integral in certain conditions, we can transfer the obtained potential to the sea surface and have access to gravity acceleration within intended places. Then having the gravity acceleration we can compute the free-air gravity anomalies. The case study evaluated in the Oman Sea contains the following stages:
1. Computation of Mean Sea level (MSL) from satellite altimetry observations.
2. Determining the Sea Surface Topography (SST) obtained via oceanographic studies.
3. Conversion of the MSL level to geoidal undulations by difference SST and MSL.
3. Converting the geoidal undulations into potential value at the surface of the reference ellipsoid using inverse Bruns formula.
4. Removal of the effect of ellipsoidal harmonic expansion to 360 degree and order computational point.
5. Upward continuation of the incremental gravity potential obtained from the removal steps to gravity intensity at the point of interest by using gradient ellipsoidal Abel-Poisson integral.
6. Restoring the removed effect at the fourth step at computational point of step 5.
In order to gain global and regional effects we applied geo-potential models. Such models have the advantage of providing us with a large covering area in a minimum of time, high speed and of certainly being economical. Future application of this research includes analyzing geological structures via interpreting gravity anomalies in any sea region.Through the due anomaly and the so-called three dimensional inverse gravity problem in space domain and frequency domain, one can determine the depth of the basement or the same sediment thickness. The methods proposed by Chakravarthi, Parker and Oldenburg apply absolution inverse problem in the space and frequency domain in the Oman Sea area, to be used for determination the sediment thickness. For determining sediment thickness via solving the inverse gravity problem in the space domain, the method of Chakravarthi, and Sundarajan is to be used. In this method density is interchanyeable with depth and to show this dependency we have made use of a parabolic function. In the basin sedimentary, gravity arising from a prism, is calculated. The method of interpretation begins by calculating the initial depth estimations of a sedimentary basin. Oldenburg deduced a method to compute the density contrast topography from the gravity anomaly reversely in a two-dimensional Cartesian coordinate system