Refining regional marine gravity anomalies based on shipborne gravity and multibeam bathymetric data

In integrated marine surveys, shipborne gravity and multibeam bathymetry are typically conducted simultaneously. While multibeam systems can achieve full coverage of a survey area, the relatively large spacing between gravity survey lines hinders the reliable estimate of gravity anomalies between tracks. Consequently, traditional data fusion methods offer limited accuracy improvements. This study proposes a method to refine satellite altimetry-derived models by using shipborne gravity tracks as constraints to extract high-frequency gravity anomalies derived from the forward modeling of multibeam bathymetry. Taking a region in the South China Sea as a case study, the proposed method improved the local accuracy of the SIO V32 and SWOT_04 models by 31.5% and 18.8%, respectively. This enhancement is primarily attributed to corrections within the ~10 km wavelength band. Notably, while this method significantly improves accuracy in areas with complex seafloor topography and high relief, its effectiveness is limited and may even lead to over-correction in flat regions. Furthermore, the SWOT_04 model exhibits stronger signals in the 10-20 km band compared to SIO V32, with its validation accuracy improved by 30.4%. Spectral analysis shows that SWOT_04 and SIO V32 achieve strong coherence (correlation coefficient >0.5) with multibeam bathymetry at wavelengths greater than 15 km and 18 km, respectively, whereas the refined gravity anomalies show strong coherence starting from 12 km. This indicates that current satellite altimetry models still lack sufficient signal in high-frequency bands in the eastern South China Sea sub-basins, which remains a key factor limiting the precision of bathymetric inversion.