Geocenter estimates from 10 years of multi-mission LEO GNSS tracking

Geocenter motion (GCM) is the relative motion of the center of mass of the Earth w.r.t. the center of figure of the solid Earth. It can be estimated from space-geodetic observations of Earth-orbiting satellites. However, geocenter estimates from the precise orbit determination of Global Navigation Satellite System (GNSS) satellites are hampered by deficiencies in solar radiation pressure modeling, the high altitude of these satellites, as well as the lacking separability of GCM-related orbit changes and clock offset estimates. Satellites in low Earth orbit (LEO) have a higher sensitivity to the geocenter motion due to their lower orbital altitude.

We present the results of a homogeneous reprocessing of 10 years of LEO data (2015-2024) with thoroughly revised LEO antenna and radiation pressure models based on 13 satellites. These include GRACE and GRACE Follow-on, Jason-2 and -3, Sentinel-3A/3B/6A, Swarm-A/B/C, and TerraSAR-X with orbit heights between 340 and 1340 km. The orbit determination is based on a reduced-dynamic approach using precise point positioning with ambiguity resolution utilizing the reprocessed GNSS orbit, clock, and bias products of the Center for Orbit Determination in Europe (CODE). 

The consistency of the geocenter estimates is evaluated by comparing the results from the different LEO missions. A combined time series is obtained and validated with geocenter estimates from Satellite Laser Ranging (SLR). This series is also evaluated with geocenter motion obtained from ECMWF reanalysis (ERA-5) atmosphere and hydrology as well as TUGO-m ocean. Finally, annual and semi-annual amplitudes and phases are compared to the ITRF2020 geocenter model as well as other geophysical and space-geodetic models.