Satellite-Based Water Surface Slope in Small Mountain River

Abstract

Satellite altimetry has become a crucial alternative for measuring inland water surface elevations apart from ground observation approaches. Water surface slope (WSS), which usually acts as a fundamental parameter in river discharge simulation, also allowing for validation of satellite water levels with differences between locations of satellite virtual stations and ground gauging stations. Various satellite data products are accessible to offer precise measurements of river water levels and estimates of WSS on a global scale. However, the use of satellites to observe the water surface of small rivers, particularly those in mountainous areas with narrow water surfaces, continues to be difficult. This study focuses on evaluating the precision of the ICESat-2 ATL03 photon height data in estimating WSS throughout the mountainous river section of Yongding River, which flows across the Hebei Province and Beijing City in northern China. The ICESat-2 ATL03 data with minimum along-track sampling interval of 0.7m makes it possible to accurately estimate the WSS for small river sections that ranged from 50 to 100m in width. A histogram-based statistical approach was used for identifying the satellite lidar photon height located right over the water surface. The eleven pairs of satellite virtual stations selected for extracting river water surface elevation and estimating river WSS demonstrated an overall validation correlation coefficient of 0.98. The range of relative error in WSS estimation is between 0.13% and 9.02%. The results of this work have important implications for using satellite-based measurements to estimate critical hydrological parameters in small and mountainous river basins when ground observations are not available.

Keywords: Satellite altimetry, Water level, Water surface slope, Mountain river, Lidar photon denoising