EPOS-OC, a Universal Software Tool for Satellite Geodesy at GFZ

Abstract

AbstractThe adjustment of parameters from different observations describing the state and change of system Earth has been conducted at the Helmholtz Centre Potsdam—GFZ German Research Centre for Geosciences via satellite observations for many decades. Satellite Laser Ranging (SLR) is used to establish ground station coordinates and their drifts as well as Earth Rotation Parameters (ERPs). Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS), Global Navigation Satellite System (GNSS), SLR and Very Long Baseline Interferometry (VLBI) observations are combined to contribute to the development of an International Terrestrial Reference Frame (ITRF) with the highest precision possible. The Earth’s gravity field and its temporal variations are adjusted analyzing orbit perturbations of Low Earth Orbiting (LEO) satellites, where the corresponding trajectories are obtained from Global Positioning System (GPS), on-board accelerometers (ACC) or gradiometers, star tracker (STR) and inter-satellite ranging observations. Apart from real data analysis, numerous simulation studies are conducted, e.g. to investigate the performance of Next Generation Gravity Missions or possible improvements of terrestrial reference frames by space-tie satellites. Also, we contribute to testing the theory of general relativity by analysing observations of the Laser Geodynamic Satellites (LAGEOS). All that would not be possible without a universal software tool that is central to all these activities. In this paper we give a short overview of our program package Earth Parameter and Orbit System (EPOS) with its core module for precise orbit computation (OC) EPOS-OC. We briefly describe its main features and give examples on Precise Orbit Determination (POD) of Earth satellites, describe how the program is used for determination of ERPs, station coordinates, reference frames and the adjustment of Earth’s gravity field using real-world data and within simulation studies. We finally show that EPOS-OC is also a useful tool to test some predictions of the theory of General Relativity.