COMPARING ICESAT-2 AND GNSS-REFLECTOMETRY WATER SURFACE PROFILES OVER THE TONLE SAP LAKE

In this paper, we compare water surface height profiles measured by the Ice, Cloud, and Elevation Satellite-2 (ICESat-2) ATL13 data product on April 25, 2023 that intersect with a GNSS-Reflectomety (GNSS-R) altimetry track collected on April 17, 2023 over the Tonle Sap Lake in Cambodia. Overall, we find reasonable agreement between the two datasets, with the nearest segment of ICESat-2 and GNSS-R tracks having a correlation of 0.79. However, some deviations exist, with the GNSS-R track measuring 7 cm lower than the ICESat2 track at an intersection point, potentially due to different lake surface conditions at the time of each measurement. This comparison is motivated by the interest in applying GNSS-R altimetry for a broader study of large inland lakes. Our focus on the Tonle Sap Lake is inspired by the lake's key role in the region combined with the difficulty in monitoring it by other techniques due to its large size, frequent cloud cover, and surrounding dense mangrove forests. GNSS-R (operating in L-band) can penetrate these environmental factors while accumulating frequent and spatially diverse water surface measurements. In total, we find 53 GNSS-R tracks collected by Spire Global between 2021 and 2023 that pass our altimetry criteria. In contrast, we find only 27 ICESat-2 tracks (each laser counted individually) through 12 total passes, likely limited by cloud cover.