To Which Extent the Surface Water Ocean Topography (SWOT) Mission Is Currently Able to Monitor Water Surface Elevation and Extent on the French Lakes?

Abstract

This study (July 2023–December 2025) assesses the SWOT satellite's ability to measure water surface elevation (WSE) and surface water extent (SWE) over diverse French lakes. WSE estimates from SWOT were compared to in situ gauge data and conventional radar altimetry, while SWE was evaluated using the Global Water Watch (GWW) database. SWOT shows good agreement with altimetry ( R ²  = 0.56, RMSE = 1.61 m), but performs less well against in situ data for small lakes (<0.5 km ² ) or in complex terrain ( R ²  = 0.1–0.5; RMSE = 0.2–1.59 m). SWE from SWOT aligns closely with GWW at the national scale ( R ² up to 0.94), with slight underestimation. Lake size and surrounding topography significantly influence data accuracy. Despite some limitations, SWOT is a valuable tool for inland water monitoring when data quality is controlled and local context is accounted for.