A method to enhance the detecting of geostrophic current and its temporal variations with SWOT swath data.

The Surface Water and Ocean Topography (SWOT) mission, which can map the sea surface height with high spatial and temporal sampling rates simultaneously, has significant potential for detecting mesoscale and submesoscale eddy variations. At present, in the determination of geostrophic current from nadir altimeter or SWOT swath data, the optimal interpolation method is usually used to grid the observations with the space-time covariance function and use a percentage of the signal variance to reduce the long-wavelength error. However, this optimal interpolation method used for nadir altimeters may not be optimal for SWOT as the spatial and temporal characteristics is different. In this study, we propose to first derive the geostrophic currents in each swath from absolute dynamic topography by difference, to reduce the long-wavelength error which is constant along the tracks. And then, based on the temporal characteristics of the signal expected to be detected and high spatial SWOT observations, the spatial covariance function is used only to get the gridded geostrophic currents. The accuracy of the proposed method is verified by one year of simulated data in the Sea of Japan using MITgcm LLC4320 model and the SWOT errors. Compared with the absolute dynamic topography and geostrophic current from LLC4320 model, using the simulated data including errors, the proposed method makes high spatial sampling more effective and can obtain gridded absolute dynamic topography and geostrophic current with better accuracy especially when the number of observations is limited. In terms of the temporal variations of eddy kinetic energy, this method can significantly improve the reconstruction and detected temporal scales of mesoscale eddy variations. [ABSTRACT FROM AUTHOR]