The calculation and analysis of along-track and cross-track crossover SSHs discrepancies from wide-swath altimetry data

Abstract

The wide-swath sea surface height (SSH) data, obtained from the Surface Water and Ocean Topography (SWOT) project, hold great significance for studying global water distribution and improving the resolution of the ocean gravity field. Compared to traditional altimeter data, the wide-swath data provide more tracks per pass, which increases the time required for calculating crossover points. To address this, the limited area method for calculating along-track and cross-track crossover points between ascending and descending passes is proposed. Based on the varying sizes of the crossover zone at different latitudes, the crossover zone can be defined within a limited area. The crossover points are then calculated from the wide-swath data within this limited area. This method is compared with other approaches, showing that it can precisely identify crossover points in a manner consistent with the latitude difference method while requiring only about one-fourth of the time. Additionally, crossover discrepancies of SWOT-measured SSHs are analyzed. Results indicate that SSH accuracy from Level 2 products is lower at the swath edges compared to the middle. The Level 3 product achieves an accuracy of approximately 0.05 m. Overall, the limited area method efficiently determines exact crossover positions and significantly reduces time consumption, and the accuracy of SSHs from the Level 2 product at the edge of the swath is lower than that at the middle of the swath. The accuracy of SSHs from the Level 3 product is consistent with that from traditional altimeters.