Performance Assessment of Surface Water and Ocean Topography (SWOT) Mission for WSE Measurement Across India

Abstract The Surface Water and Ocean Topography (SWOT) mission, launched in December 2022, is the first wide‐swath altimetry mission designed to improve our understanding of surface water dynamics through high‐resolution water surface elevation (WSE) and extent measurements. This study presents the first‐hand validation of SWOT WSE data from April 2023 to December 2024 across 419 stations in India, analyzing 14,892 SWOT WSE observations. Our findings indicate that SWOT performs well for rivers wider than 100 m, with a Spearman's correlation ( ρ s ) exceeding 0.88 for the 68th percent of stations with a relative error (RE) in WSE of 18 cm. Even for narrower rivers, SWOT achieves accuracies exceeding expectations (RE of 25.78 cm). Over reservoirs, SWOT demonstrates strong performance, with RE values of 10.80 cm (node product) and 13.64 cm (lake product), while maintaining ρ s above 0.65 for all reservoirs analyzed, highlighting SWOT's robust potential for monitoring diverse water bodies in India.