An improved triple collocation-based integration of multiple gravity anomaly grids from satellite altimetry: Contribution of ICESat-2

Satellite altimetry has been widely used to determine the marine gravity fields. Different altimeter missions lead to different gravity grids with varying spatial resolutions and accuracies. Marine gravity accuracy in offshore waters is often low. Integrating marine gravity anomalies (MGA) derived from various altimeter missions are key to obtaining high-precision and high-resolution global marine gravity fields. Here an improved triple collocation (ITC) method is first proposed to establish a new 1´×1′ marine gravity anomaly in the South China Sea (SCS), named MGAITC, by merging the grids of MGA from the Haiyang-2A (HY-2A), CryoSat-2, and ICESat-2 altimeter measurements. A combined MGA (MGACOM) is also constructed by using the least squares collocation (LSC) method from three sets of altimeter-derived geoid gradients. The qualities of MGAITC, MGACOM and each altimeter-derived MGA grids are assessed using shipborne gravity and different global gravity models over waters of varying depths and distances from the coastline. The accuracy of the MGAITC gravity against the shipborne gravity is 5.52 mGal, which represents improvements of 7%, 9%, 13%, and 3% relative to the gravity grids derived only from ICESat-2, CryoSat-2, HY-2A and from MGACOM. In all assessments involving different sub-regions, seafloors, and distances from the coastline, MGAITC performs the best, and ICESat-2 yields the best single-mission MGA grid, especially in offshore waters. We find that ICESat-2 has a high potential to improve shallow-water gravity accuracy and the global marine gravity field can be improved by integrating gravity grids from different altimetry missions using ITC.