Abstract:

The SWOT satellite, operating in a wide-swath interferometric altimeter mode, is expected to overcome the limitations of traditional nadir altimetry satellites for sea surface height observations, thereby improving the precision and spatial resolution of marine gravity anomaly measurements. In this study, shipborne gravity data provided by Sun Yat-sen University, National Yang Ming Chiao Tung University, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), and National Centers for Environmental Information (NCEI) were utilized to systematically evaluate the accuracy and power spectral characteristics of the SWOT_02, DTU21, V32.1, NSOAS24, and SDUST22 global gravity anomaly models over the Chinese coastal and offshore areas. Particular attention was given to assessing the performance of the SWOT_02 model, which incorporates data from the SWOT satellite, as an enhancement of the V32.1 model. Results indicate that, over the open ocean areas, the SWOT_02 model performs optimally. Specifically, the root mean square (RMS) of the differences between the SWOT_02 model and JAMSTEC shipborne gravity anomalies is less than 4 mGal, reflecting an improvement of approximately 1.3 mGal compared to the V32.1 model, with a corresponding relative accuracy enhancement of ~25%. Furthermore, the SWOT_02 model demonstrates the highest coherence with shipborne gravity anomalies across different wavelength bands, with its power spectral density in the wavelength range below 7 km outperforming those of the DTU21, V32.1, and NSOAS24 models. Additionally, in both the Chinese coastal seas and the deep-water regions of the South China Sea, comparison of spectral characteristics along shipborne survey tracks indicates that the SWOT_02 model exhibits significantly higher coherence with shipborne gravity anomalies provided by Sun Yat-sen University within the 7~60 km wavelength range compared to other models. Compared to other models, SWOT_02 demonstrates significantly improved coherence with seafloor topography at wavelengths shorter than 20 km. However, in some nearshore and shallow sea regions, the accuracy of the SWOT_02 model remains inferior to that of models such as DTU21 and SDUST22. This may be due to the limited quality of currently available SWOT observations, the relatively low accuracy of the base V32.1 model, and the lack of significant improvements in data processing methods for coastal areas. The complex nearshore environment poses substantial challenges for processing SWOT data, highlighting the need for further research to improve the accuracy of marine gravity anomaly models in coastal areas.

Key words: SWOT, satellite altimetry, shipborne gravity, global marine gravity model, power spectrum analysis