Evaluation of Sentinel-3 and Sentinel-6 Derived Water Levels Using in Situ Data Over Narrow Rivers

Inland water level and its dynamics are key components in global water cycle and land surface hydrology, significantly influencing water resource management, biodiversity, and climate change impacts. Space-based altimetry observations of inland water surface elevation is an important data source to supplement the limited in-situ measurements. In this study, the evaluation of Sentinel-3 and Sentinel-6 MF derived water levels was conducted over Douro and Danube rivers. However, it is still very challenging to obtain accurate water level measurements over narrow rivers, with width less than 300m. Gauge measurements were utilized for the validation of altimetry-derived water levels. Two outlier detection methods were applied for data pre-processing to improve the accuracy of measurements. The root-mean-square-error (RMSE) of the Sentinel-6 mission over Danube River is 0.57m, while the mean-RMSE of the Sentinel-3 over Douro River is 2.12m.