Kinematic orbits and their contribution to monitoring Earth's gravity field

Abstract

<p>For the observation of temporal mass variations on Earth, the determination of the Earth's gravity field is of great importance. Therefore, additional concepts are required to bridge possible gaps occurring within dedicated gravity field missions such as CHAMP, GRACE and GOCE or between consecutive gravity field missions i.e., GRACE and GRACE Follow-On. Gravity field solutions based on kinematic orbits of low earth orbiting (LEO) satellites are a common practice. Our working group use an in-house developed approach based on an iterative least-squares adjustment utilizing raw GNSS observations for the kinematic orbit determination. Since varying algorithms, models, and processing strategies applied by different institutions can lead to inconsistencies, which affects the performance we now use GNSS products which are consistently processed with our in-house software package GROOPS.  As a result, improved kinematic orbit and subsequently gravity field solutions could be achieved due to this consistency. Up to now, we reprocessed the kinematic orbits of 19 LEO satellite missions, including non-gravity missions like Sentinel 1A/B, Sentinel 3A/B, Swarm A/B/C, TerraSAR-X, TanDEM-X, MetOp A/B, and Jason 1/2/3. On our website we subsequently publish these kinematic orbit solutions together with further satellite orbit products like the reduced dynamic orbit, the attitude, and the accelerations due to non-conservative forces.  Based on these kinematic orbits a time series of individual monthly gravity field solutions has been determined. Additional to more precise orbits, enhanced non-gravitational force models based on satellite macro models contribute to more accurate gravity field solutions. The time series spans meanwhile 20 years without gaps, starting in January 2002. For this time span, we will show the mass variations for regions such as Greenland, the Amazon basin and other large river basins and compare the results derived from the kinematic orbits with those from COST-G Swarm and COST-G GRACE/GRACE-FO.</p>