Evaluation of the accuracy of SWOT satellite observations for monitoring lake water levels in the Yangtze River Basin

Abstract

To evaluate the capability of the newly developed SWOT satellite for lake water level retrieval and basin-scale hydrological monitoring, this study selected 513 lakes larger than 1 km 2 in the Yangtze River Basin. SWOT L2 HR Raster data from November 2023 to May 2025 were used to extract lake water levels, and their accuracy was assessed using DAHITI, ICESat-2, CryoSat-2, and in situ hydrological station observations. During the study period from November 2023 to May 2025, SWOT obtained at least one valid water level observation for 501 of the 513 lakes, corresponding to a lake coverage rate of 97.66%, and more than 80% of the covered lakes accumulated more than 10 valid observations. The mean number of valid observations per lake for SWOT was 22.7, which was 18.6 and 18.4 observations higher than those of ICESat-2 and CryoSat-2, respectively; SWOT also provided valid observations for 98 and 121 more lakes, respectively, significantly expanding the coverage of lake water level monitoring in the Yangtze River Basin. Validation against multi-source satellite altimetry showed good agreement, with Bias ranges of − 0.659 to 0.158 m, − 0.142 to 0.263 m, and − 0.499 to − 0.013 m, and RMSE ranges of 0.153–0.801 m, 0.089–0.818 m, and 0.124–0.891 m, respectively. Validation using Dongting Lake hydrological stations yielded Bias, RMSE, and MAE values of − 0.007 to 0.068 m, 0.137–0.198 m, and 0.116–0.178 m, with correlation coefficients greater than 0.99. These results demonstrate that SWOT can substantially improve lake water level monitoring in the Yangtze River Basin.