ICE2WSS; An R package for estimating river water surface slopes from ICESat-2

River water surface slopes (WSS) can improve the performance of rating curves for discharge estimates and provides information about river hydraulic processes and phenomena. Utilizing the beam pattern of ICESat-2, the WSS can be estimated by the slope of a linear regression of the water surface elevation and the distance along the river. This paper presents a robust processing scheme for calculating WSS along rivers in the SWOT River Database. We demonstrate the processing scheme for the Amur River basin using four years of data. This yields 7306 WSS estimates across 1693 reaches approximately 10 km in length. The slopes were estimated between 0.60 cm/km and 651.04 cm/km with a median standard error of 0.47 cm/km. The method works for slopes larger than 0.5 cm/km and river widths larger than 50 m. The software presented in this paper is available as the R package ICE2WSS on Github (https://github. com/lindchr/ICE2WSS).