Zum Einsatz kinematischer Orbits für die zeitvariable Schwerefeldbestimmung

Abstract

Physical geodesy focuses on measuring the Earth’s external gravity field and analyzing its spati al and temporal variations. These variations are primarily quantified using data from dedicated satellite gravity field missions. However, observational data from other satellites in low Earth orbit (LEO) can be utilized to capture large-scale gravity field structures and their temporal changes. Gravity field information can be extracted from the kinematic positions of LEO satel lites, thereby extending the observational record of dedicated satellite gravity field missions. Kinematic orbits of various LEO satellite missions are routinely determined by independent institutions such as the Institute of Geodesy (IFG) at Graz University of Technology and the Astronomical Institute of the University of Bern (AIUB), based on GNSS code and phase ob servations, and are made available for further analysis. In this study, gravity field information is derived from the kinematic orbits of GRACE (2002–2017) and Swarm (since 2013) missions in the form of monthly spherical harmonic coefficients using the short-arc approach implemented in the GROOPS software. Several influencing factors are investigated, including the maximum degree of the spherical harmonic expansion, the temporal resolution of the orbits, and the arc length. The quality of the resulting solutions is evaluated through comparison with ITSG-Grace monthly solutions, which are based on inter-satellite ranging observations from the GRACE( FO) missions. The results demonstrate that large-scale mass redistributions can be reliably detected, and that accuracy can be further improved by combining data from multiple satellite missions.