Validation of SWOT satellite derived inland water surface heights using ground based lake level measurements

This study presents the first regional validation of water surface elevation (WSE) measurements derived from the Surface Water and Ocean Topography (SWOT) satellite in Türkiye, focusing on three hydrologically distinct inland water bodies: Lake Burdur (a natural lake), Lake Van (a deep alkaline lake), and the Çatalan Dam Reservoir (a managed artificial reservoir). SWOT-derived WSE were assessed against State Hydraulic Works (DSİ) ground-based observations. Initial comparisons revealed substantial discrepancies, with correlation coefficients below 0.30 and root mean square errors (RMSEs) exceeding 0.77 m, highlighting the need for further refinement. To improve accuracy, data filtering based on SWOT quality flags and the exclusion of observations with high WSE standard deviations and uncertainties were applied. These steps enhanced the correlation coefficients above 0.51 and reduced RMSEs to below 1.27 m. Systematic underestimations were observed for Lake Van and Çatalan Dam, whereas both under- and overestimations occurred for Lake Burdur. Applying the median of residuals as a bias correction further decreased RMSEs to below 0.37 m across all study sites. These results underscore the potential of SWOT for monitoring inland water bodies in regions experiencing water scarcity, such as Türkiye, while emphasizing the importance of advanced data processing, integration of high-resolution geoid models, and continued cross validation with in situ measurements. The proposed methodology, both computationally efficient and straightforward, offers a transferable framework for improving SWOT-based WSE and ultimately SWOT derived river discharge estimations based on WSE values across diverse inland water systems worldwide.