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Abstract

The recent Surface Water Ocean Topography (SWOT) altimeter mission measures two-dimensional SSHs along two 50-km-wide swaths and one-dimensional SSHs along the nadir track, providing a significant opportunity to improve the accuracy and resolution of geoid gradients essential for marine gravity modeling. This study investigates the accuracy of determining north and east components of geoid gradients using simulated SWOT SSHs in the northern part of the South China Sea. SWOT SSH data were simulated using ocean depths from multi-beam and the GEBCO_2020 bathymetry model and the DTU mean sea surface. According to the unique characteristic of high-resolution two-dimensional SWOT SSH observations, we developed a new method that determines north and east components of geoid gradient at the grid point based on geoid gradients computed in along-, cross- and middle-track directions using the least-squares adjustment (LSA). For comparison purpose, the gradient components were also computed using the least-squares collocation (LSC). The accuracy of determined gradient components is assessed using the quasi-true values of gradients computed by numerical differentiations from the SWOT simulation model. The RMSE results are 0.51 (0.42) microrad and 1.12 (0.91) microrad for LSA (LSC) estimates of north and east components, respectively, in the study area. The results indicate that the LSA gradient solution is computationally efficient and compatible with those by the LSC. The SWOT mission significantly improves the accuracy of estimated gradient components when compared to Jason-2 and Cryosat-2.