Enhancing Marine Gravity Field Precision Using SWOT Wideswath Altimetry Data: a Comparative Analysis with Traditional Altimetry Satellites

Objectives: Surface Water and Ocean Topography (SWOT) mission, a wide-swath altimeter satellite, measures sea surface heights (SSHs) with unparalleled spatial resolution and precision, offering new opportunities to enhance the precision and resolution of the existing marine gravity fields. However, there is currently limited research on recovering marine gravity fields from SWOT, particularly with respect to quantitative assessments of the accuracy of SWOT-derived marine gravity field. This study investigates the potential of SWOT in determining deflection of the vertical (DOV) and deriving marine gravity anomalies based on simulated SWOT data. Methods: In the northern South China Sea around Dongsha Island, we generate the high-wavenumber SSH components using multi-beam depths based on the residual depth model principle, compensating for the losing high-frequency signals of the DTU21MSS model. Then we simulate wide-swath SWOT SSH observations with 1.4cm precision and 2 km×2 km spatial resolution. In order to explore the advantages of SWOT in recovering marine gravity field over the conventional nadir-looking altimeter satellites, we also simulate SSH data for Jason-2 and Cryosat-2. To make the most of SWOT’s wide-swath altimetry nature, we separate two-dimensional SSHs into along- and cross-track directions. We use least-squares collocation (LSC) and weighted least-squares adjustment (WLSA) to estimate the north and east components of DOV and derive marine gravity anomalies using inverse Vening-Meinesz formula. The “true values” of DOV components and gravity anomalies are computed within the simulation of SWOT data to evaluate the precision of the results. Results: The LSC method outperforms WLSA in estimating the DOV components. Averaging multi-cycle SWOT data efficiently suppresses observation errors. SWOT along-track data are beneficial for estimating the north components of DOV, while the cross-track data are useful for resolving the east components. In the study area, the precision of both the north and east components of DOV estimated from the merged Jason-2 and Cryosat-2 data is about 3 microrad, thereby deriving 1′×1′ gravity anomalies with 4.7-mgal precision. Using SWOT data, the precisions of the two DOV components and gravity anomalies improve to 0.7 microrad and 1 mgal, respectively. Conclusions: Compared to conventional altimeters, the SWOT wide-swath altimetry significantly improves the accuracy of marine DOV and gravity fields.