Abstract:
Reliable monitoring of standing water bodies, and in particular their water level, is of critical importance for water resource management, hydropower operations, climate change adaptation, and, not least, the prevention of anthropogenic hazards. Remote sensing provides a robust alternative to traditional in situ measurements, offering large-scale and regular coverage of the areas of interest. This study presents the application of a combined approach for water level assessment based on the integrated use of optical data from the MSI sensor onboard Sentinel-2 (ESA, 2025) and LiDAR measurements from the GEDI (Global Ecosystem Dynamics Investigation) mission (UMD, 2025). The method involves delineating the water surface from Sentinel-2 (S-2) imagery using spectral indices (NDWI, MNDWI) and deriving the elevation of the water surface from GEDI profiles. The integration of these two data sources enables simultaneous spatial and vertical characterization of the water body. The case study focuses on the “Kardzhali” Reservoir, located in the Eastern Rhodope Mountains, with analyses performed for the summer months of 2023. The spatial masks of water extent were generated through morphological processing of MSI data and revealed a water surface area of approximately 10 km². S-2 scenes were carefully selected to coincide with GEDI ground tracks crossing the water surface, thereby providing 115 elevation points with an average level of 351.80 m a.s.l. and a variation below 0.20 m. The obtained results confirm the applicability of the proposed method for the joint use of S-2 and GEDI data and demonstrate the potential of the integrated approach for reliable monitoring of standing water bodies. Despite limitations related to the discrete coverage of GEDI and the dependence of S-2 on cloud-free conditions, the method proves suitable for reservoirs with well-defined shoreline boundaries.