Abstract
With new Ice, Cloud, and land Elevation Satellite (ICESat)-2 lidar (Light detection and ranging) datasets and classical Landsat imagery, a method was proposed to monitor annual changes of lake water levels and volumes for 35 years dated back to 1980s. Based on the proposed method, the annual water levels and volumes of Lake Mead in the USA over 1984–2018 were obtained using only two-year measurements of the ICESat-2 altimetry datasets and all available Landsat observations from 1984 to 2018. During the study period, the estimated annual water levels of Lake Mead agreed well with the in situ measurements, i.e., the R2 and RMSE (Root-mean-square error) were 1.00 and 1.06 m, respectively, and the change rates of lake water levels calculated by our method and the in situ data were −1.36 km3/year and −1.29 km3/year, respectively. The annual water volumes of Lake Mead also agreed well with in situ measurements, i.e., the R2 and RMSE were 1.00 and 0.36 km3, respectively, and the change rates of lake water volumes calculated by our method and in situ data were −0.57 km3/year and −0.58 km3/year, respectively. We found that the ICESat-2 exhibits a great potential to accurately characterize the Earth’s surface topography and can capture signal photons reflected from underwater bottoms up to approximately 10 m in Lake Mead. Using the ICESat-2 datasets with a global coverage and our method, accurately monitoring changes of annual water levels/volumes of lakes—which have good water qualities and experienced significant water level changes—is no longer limited by the time span of the available satellite altimetry datasets, and is potentially achievable over a long-term period.
Highlights
Lakes and reservoirs only cover a small portion of the Earth’s surface, they are of great importance for human well-being, biodiversity, and ecosystem from local to global scales [1]
This study focused on a method to calculate annual water levels and volumes over 1984–2018
Applying the MNDWI method, yearly Lake Mead boundaries between 1984 and 2018 with the polyline format were extracted from all available Landsat Thematic Mapper (TM)/ETM+ images, and, for example, in Figure 1, blue curves illustrate the Lake Mead boundary in 2016
Summary
Lakes and reservoirs only cover a small portion of the Earth’s surface, they are of great importance for human well-being, biodiversity, and ecosystem from local to global scales [1]. In situ measurements were used to obtain water levels/volumes of some specific lakes [6]. In situ data of water levels/volumes of lakes across the globe are very limited, especially for developing countries and some remote areas. Multiple satellite sensors have a potential for monitoring lake water levels and volumes at a global scale owing to their global spatial coverage. Many methods were proposed and exhibited a good performance for monitoring lake water levels and volumes [6,11,12,13,14,15,16]. For some small lakes, water level observations from ICESat and radar altimeters may be very limited due to their large footprints (i.e., 70 m and hundreds of meters in diameter) and their limited time coverages of satellite altimetry data [2,17]
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