Investigation of a suitable geometric design for the CONT14 observation network to improve the accuracy of EOPs by construction of VLBI stations in Iran

Document Type : Research Paper

Authors

1 Assistant Professor, Department of Surveying, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

2 M.Sc. Student, Department of Surveying, Faculty of Civil Engineering, University of Tabriz, Tabriz, Iran

Abstract

Very long baseline interferometry (VLBI) has been used since the mid-1960s as a spatial geodetic tool for accurately determining coordinates on the ground, determining the Earth's rotational axis with very high accuracy and extracting important parameters related to earth. The most important products of VLBI data processing are Earth Orientation Parameters (EOPs) and International Celestial Reference Frames (ICRFs). Other important parameters can be determined by VLBI are International Terrestrial Reference Frames (ITRFs), light deflection parameter, motion parameters of tectonic plates, Love and Shida numbers and ionospheric and tropospheric parameters. The basic principle of VLBI is measuring the time difference between the arrival time of a radio wave in two or more antennas, which is referred to as the time delay. To achieve this purpose, first the atomic clock must be used and secondly the clocks in the antennas must be synchronous. Earth orientation parameters (EOPs) are a set of parameters that describe irregularities in the Earth's rotation. The VLBI method can be used to derive EOPs. These parameters can be used for transformation between international terrestrial reference frame (ITRFs) and celestial reference frame (ICRFs) or vice versa. This transformation takes place through a sequence of rotations related to precession/nutation (NUTX, NUTY), earth rotation (Dut1) and polar motion (XPO, YPO). The geophysical effects of the Earth as well as the effects of celestial bodies such as the Moon or the Sun on the Earth's rotation, lead to changes in the EOPs; therefore, changes in geophysical parameters of the earth can be obtained from changes in the EOPs. The purpose of this study is to investigate the accuracy of the EOPs after adding new observation stations to the CONT14 observation network. These observation stations are artificially constructed in Iran and the accuracy of EOPs before and after adding new station to the network is investigated. CONT sessions are one of the most famous and important sessions in which the stations collect data continuously for two weeks. On average, the CONT sessions take place every three years. Due to the large amount of data in these sessions, the EOPs are determined with high accuracy. Due to the importance of CONT sessions, we will investigate the effect of constructing stations in Iran on the accuracy of the EOPs in one of the CONT sessions, which will be added to the CONT14 observation network. Due to the high cost of constructing a VLBI observation station and to approaching reality, we will add five stations to the network in maximum case. The local network resulting from the five new stations covers the whole of Iran and the locations of these five stations have been chosen arbitrarily. With analyzing the data that collected by the CONT14 session, the accuracy of the EOPs is obtained. After adding new observation stations to CONT14 network and performing the new session, the collected data is processed again and the accuracy of the EOPs is obtained. A comparison of the accuracy obtained in the new mode with accuracy obtained in CONT14 session shows the degree of improvement of EOPs accuracy. By comparing EOPs precision in all possible observation networks, we came to the conclusion that if four observation stations are constructed in Tabriz, Ahvaz, Chabahar and Mashhad and add them to the CONT14 observation network we can improve CONT14 EOPs accuracy by about 13.28%.

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