Abstract
Although the Advanced Topographic Laser Altimeter System (ATLAS) onboard the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) was primarily designed for glacier and sea-ice measurement, it can also be applied to monitor lake surface height (LSH). However, its performance in monitoring lakes/reservoirs has rarely been assessed. Here, we report an accuracy evaluation of the ICESat-2 laser altimetry data over 30 reservoirs in China using gauge data. To show its characteristics in large-scale lake monitoring, we also applied an advanced radar altimeter SARAL (Satellite for ARgos and ALtika) and the first laser altimeter ICESat (Ice, Cloud and land Elevation Satellite) to investigate all lakes and reservoirs (>10 km2) in China. We found that the ICESat-2 has a greatly improved altimetric capability, and the relative altimetric error was 0.06 m, while the relative altimetric error was 0.25 m for SARAL. Compared with SARAL and ICESat data, ICESat-2 data had the lowest measurement uncertainty (the standard deviation of along-track heights; 0.02 m vs. 0.17 m and 0.07 m), the greatest temporal frequency (3.43 vs. 1.35 and 1.48 times per year), and the second greatest lake coverage (636 vs. 814 and 311 lakes). The precise LSH profiles derived from the ICESat-2 data showed that most lakes (90% of 636 lakes) had a quasi-horizontal LSH profile (measurement uncertainty <0.05 m), and special methods are needed for mountainous lakes or shallow lakes to extract precise LSHs.
Highlights
Lakes and reservoirs are highly sensitive to climate change [1,2] and human activities [3]
From October 2018 to May 2019, the ICESat-2 has covered about three-fourths of lakes (636 out of 862) of HydroLAKES
The great relative error of Fengman Reservoir was mainly caused by two abnormal observations (Figure 3(6)) when the reservoir began to thaw and when the stream bed was exposed as the water level dropped
Summary
Lakes and reservoirs are highly sensitive to climate change [1,2] and human activities [3]. Monitoring their dynamics from space is important for water management and drought monitoring [4,5,6,7], especially for remote and less developed regions where hydrological data is rare or hard to access [8,9]. Spatial, temporal gaps, and altimetric error are three main evaluation factors that should be considered in evaluating whether an altimeter is suitable for large-scale lake monitoring
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