Enhancing the Reconstruction of Mesoscale Signal Mapped With Surface Water and Ocean Topography Mission

The surface water and ocean topography (SWOT) mission offers significant potential in mapping sea surface height (SSH) for detecting mesoscale and submesoscale ocean signals. However, possible spurious signals caused by long-wavelength error (LWE) during SSH mapping pose a challenge in realizing the potential. We improved the widely used optimal interpolation method, to reduce the spurious mesoscale signal for SWOT. Since LWE remains in the SWOT SSH observations after cross-track calibration, the spatial differenced SSH observations instead of SSH observations were used as input for the mapping. The method was assessed using the observing system simulation experiment (OSSE) and SWOT level 3 ocean products. The results show that LWE mainly has an effect on the mesoscale signal with wavelengths longer than 100 km, and the improved method can reduce spurious signals significantly compared to the standard optimal interpolation (SOI) method. In addition, compared to the empirical optimal interpolation (EOI) method commonly used in LWE reduction, the improved method has a comparable performance and no longer requires prior variance of LWE. For the uncorrected SWOT level 3 ocean products, the decimeter-level LWE can be reduced by the improved method and the mesoscale signal covered by it is successfully reconstructed. For the cross-track calibrated SWOT level 3 ocean products, residual centimeter-level LWE can also be reduced, and the signal-to-noise ratio (SNR) of mesoscale signals is improved by 62% for wavelengths longer than 100 km.