Inland water level measurement from spaceborne laser altimetry: Validation and comparison of three missions over the Great Lakes and lower Mississippi River

Satellite laser altimetry offers an opportunity to accurately measure inland water levels over the Earth’s surface. This paper described the validation and comparison of three spaceborne missions for inland water level retrievals, including the Geoscience Laser Altimeter System (GLAS) onboard the Ice, Cloud and Land Elevation Satellite-1 (ICESat-1), as well as the newly launched Advanced Topographic Laser Altimeter System (ATLAS) onboard ICESat-2 and the Global Ecosystem Dynamics Investigation (GEDI) lidar on the International Space Station. This study was conducted over the Great Lakes and lower Mississippi River using in-situ data from 22 gauging stations, where the potential for monitoring inland water dynamics was explored. The results showed that ICESat-2 provided lake water level retrievals with an unprecedented accuracy (RMSE = 0.06 m, biases =−0.01 ± 0.05 m), followed by ICESat-1 (RMSE = 0.10 m, biases = −0.04 ± 0.10 m), and then by GEDI (RMSE = 0.28 m, biases = −0.10 ± 0.23 m). ICESat-2 also offered more accurate river water level measurements (RMSE = 0.12 m, biases = −0.08 ± 0.07 m) than those of ICESat-1 (RMSE = 0.25 m, biases = −0.18 ± 0.16 m) and GEDI (RMSE = 0.40 m, biases = −0.24 ± 0.24 m). The analysis suggested that for all the altimeters, the strong beam achieved higher water level accuracies than those of the weak, and the nighttime acquisitions were slightly more accurate than those of the daytime. However, our result indicated no considerable differences between measurement accuracy and river width. Furthermore, the analysis demonstrated their great potential in monitoring inland water dynamics, especially with the combination of ICESat-2 and GEDI platforms. This study provided a comprehensive understanding of measurement accuracies of three recent missions and recommended that end users should employ the strong beam data acquired during the nighttime for accurate water level retrievals.