An Improved Latitude Difference Method for SWOT Accuracy Evaluation Using Crossover Discrepancies

The surface water and ocean topography (SWOT) mission is currently operating in scientific orbit. The Ka-band radar interferometer (KaRIn) altimeter represents a significant departure from nadir altimeters, offering abundant observations that would greatly advance oceanographic research. However, the accuracy of altimetry data is crucial to the validity of research results and must be evaluated using crossover discrepancies to obtain prior estimations. Traditional methods are not fully suited to the wide-swath data and tend to be inefficient when processing massive amounts of data. In this study, we propose an improved latitude difference method for calculating crossover discrepancies. The reliability of this algorithm is verified using both along-track and across-track split data. The results indicate that the accuracy of crossover discrepancies for SWOT is comparable to those of conventional altimetry satellites, confirming the performance of the SWOT low-rate L2 KaRIn product. The standard deviation of crossover discrepancies between SWOT and other satellites in the South China Sea (SCS) is about 8 cm, around 6 cm in the Indian Ocean (southern) (IOS), and approximately 8 cm in the Gulf of Mexico (GOM), further proving the accuracy of the SWOT data. Analyzing the discrepancies beyond 50 km offshore, the results demonstrate that the KaRIn altimeter is influenced by the coastline, while its performance improves in the open ocean. By leveraging the vectorization algorithm, the efficiency has been improved significantly. The computation speed of crossover discrepancies using the improved latitude difference method is around 0.006 s per point, faster than the traditional method, demonstrating that the algorithm is efficient.