Temporal Gravity Field Recovery Using The Swarm Mission Constellation High-Low GPS Tracking Data And Energy Balance Approach

The NASA/DLR's joint temporal gravity satellite mission, the Gravity Recovery And Climate Experiment (GRACE), ceased operation in July 2017, with the instruments and data degraded even earlier, contaminating the quality of retrieved gravity change signals. Even though its successor, the GRACE Follow-On (FO) twin-satellite mission was successfully launched on May 2018, the official products will not be available until approximately 2019 due to the commissioning and validation activities. Therefore, there has been and will continue to have a prolonged ( two-year) data gap between GRACE and GRACE-FO missions. ESA's Swarm 3-satellite constellation mission, which was launched in November 2013 and is expected to operate until 2021, could fill the data gap for the long wavelength component of the temporal gravity field signals using high-low GNSS tracking data. Our multi-national team is tasked by ESA to produce low-degree temporal gravity field from such data gathered by the Swarm constellation. The Energy Balance Approach (EBA) has demonstrated it can recover temporal gravity solutions using GRACE low-low KBR tracking data, with commensurate accuracy as the existing GRACE data products. Earlier studies have also demonstrated the feasibility of EBA estimated static gravity field using CHAMP and GOCE satellite GPS data derived kinematic orbits to enable the gravity field solutions to be bias-free with respect to the a priori or referenced gravity field model. The EBA is one of the several other solution approaches in ESA's Swarm gravity field project. Here, we present the initial solutions of the EBA-based long wavelength temporal gravity field solutions from Swarm constellation kinematic orbits. The solutions are then evaluated via comparisons with solutions from several other different approaches by the ESA Swarm project members, and via comparisons with the temporal gravity solutions concurrent during the GRACE data span.