Simulation analysis of geoscience applications in recovering HIS time-varying gravity signals based on relative orbit determination of giant constellations

This paper proposes a method to recover time-varying gravity signals by using relative orbit determination technology between satellites in giant constellations. This study focuses on two relative orbit determination observation modes and conducts a closed-loop simulation experiment with three constellation configurations: A (2 orbital planes, 400 satellites), B (20 orbital planes, 400 satellites) and C (20 orbital planes, 4000 satellites), for recovering the time-varying gravity signal for the HIS (Hydrology, Ice, Solid Earth). The performance was analyzed for seismic and land water monitoring, and compared with the results from the GRACE/Bender observation modes. The closed-loop simulation accounts for error sources like observation noise, tidal model errors and de-aliasing model errors, with relative orbit determination accuracy for giant constellations set to 1 mm. The recovery accuracy of HIS signals across four 7-day periods (before and after the 2004 Sumatra earthquake) was compared for different configurations. The results show the following: (i) Relative orbit determination technique significantly improves the recovery accuracy of middle-to-high-degree (high-frequency) time-varying gravity signals compared to absolute orbit determination. The C constellation demonstrates the largest improvement, with accuracy enhancements of up to 5 ~ 7 times. (ii) The accuracy of the recovered time-varying gravity signal using relative orbit determination in the C constellation is superior to that of GRACE in the degree range of 10 to 50, and about 2 times better than GRACE at degree 20. It also compares favorably with Bender at low degrees. (iii) Spatial domain analysis shows that relative orbit determination in constellation C effectively recovers HIS signals up to degree 30. It can also monitor time-varying gravity signals caused by large earthquakes (such as the Sumatra earthquake), and monitor hydrological and glacial signals in multiple regions, with precision superior to GRACE but slightly inferior to Bender. The research demonstrates that a giant satellite constellation has significant potential for monitoring changes in Earth's gravity field using relative orbit determination, and can be a valuable technical approach for future geoscientific applications in giant satellite constellation missions.