Leveraging the Potential of Sentinel-3 and SWOT Radar Altimeters for Hydrological Monitoring in Vegetated Wetlands

Wetlands are among the most productive ecosystems on Earth but also one of the most threatened by environmental and climate changes. Detailed spatial and temporal monitoring of water level patterns in wetlands is crucial to understanding the ecosystem status and dynamics, as it provides information about the amount of water stored and moving through a wetland at a given time. Space-based hydrologic monitoring of wetlands has successfully complemented ground-based hydrological observations by providing invaluable measurements of water levels and their changes over time in both gauged and ungauged areas. Detection of wetlands’ water level beneath vegetation cover requires active remote sensing technologies, where several technologies such as radar and laser altimetry, SAR amplitude, and Interferometric SAR have been successfully used. The increasing availability of data from new missions poses an opportunity to advance space-based hydrological applications, but it requires a consistent evaluation of the accuracy for such a purpose.

This study evaluates the new generation of satellite radar altimeters, including Sentinel-3 and SWOT-nadir observations, for water level retrieval in vegetated wetlands. The evaluation was conducted in the South Florida Everglades using the Altimetry Time Series (AlTiS) software with data acquired between 2023–2024. We used gauge data from the Everglades Depth Estimation Network (EDEN) as a reference for the analysis. Preliminary results show that both products provide accurate water level retrievals for the tested locations, with Root Mean Square Error (RMSE) of 0.02 m and R² of 1.00 for Sentinel-3 (n = 24), and RMSE of 0.12 m and R² of 0.99 for SWOT-nadir (n = 29). The results provide a first insight into the potential of both missions for tracking water level changes in vegetated wetlands and open new opportunities to strengthen hydrological monitoring in unmonitored areas. The next steps of the research will include performing a systematic evaluation of the products for various wetland types and exploring the potential of integrating the observations with additional datasets in multi-sensor approaches.