The Influence of Lake Size on the Accuracy of Satellite-Derived Water Level Measurements (SWOT)

The accuracy of satellite-derived water surface elevation (WSE) measurements is crucial for hydrological studies and water resource management. This research investigates how lake area influences the accuracy of such measurements by analyzing preliminary data from 53 Swedish lakes, categorized by size: small (<1 km²), medium (<10 km²), large (<100 km²), and extra-large (>100 km²).

WSE measurements were obtained from the first year of the Surface Water and Ocean Topography (SWOT) mission's science orbit, specifically using the Pixel Cloud Product, which provides high-resolution observations of Earth's surface water bodies. The SWOT mission employs Ka-band radar interferometry to capture detailed spatial and temporal variations in WSE, aiming to enhance our understanding of global hydrology.

We compared the SWOT-derived WSE data with high-accuracy in-situ observations provided by the Swedish Meteorological and Hydrological Institute (SMHI) between August 2023 and May 2024. Many of these in-situ observations were collected from rivers near the 53 Swedish lakes, which might contribute to the analysis of river systems in addition to lakes.

Initial findings reveal a significant dependency of measurement accuracy on lake size. Smaller lakes exhibit higher Root Mean Square Error (RMSE) in satellite-derived WSE measurements compared to larger lakes. These results underscore the impact of lake area on the reliability of satellite-based hydrological data.

While preliminary, this study offers valuable insights for refining satellite hydrology techniques and enhancing their applicability to smaller and more complex lake systems. The implications of our findings suggest the need for improved algorithms or calibration methods to increase the accuracy of SWOT measurements in small water bodies, benefiting water resource management and hydrological modeling.