Abstract
Abstract. Supraglacial lakes and melt ponds occur in the ablation zones of Antarctica and Greenland during the summer months. Detection of lake extent, depth, and temporal evolution is important for understanding glacier dynamics. Previous remote sensing observations of lake depth are limited to estimates from passive satellite imagery, which has inherent uncertainties, and there is little ground truth available. In this study, we use laser altimetry data from the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) over the Antarctic and Greenland ablation zones and the Airborne Topographic Mapper (ATM) for Hiawatha Glacier (Greenland) to demonstrate retrievals of supraglacial lake depth. Using an algorithm to separate lake surfaces and beds, we present case studies for 12 supraglacial lakes with the ATM lidar and 12 lakes with ICESat-2. Both lidars reliably detect bottom returns for lake beds as deep as 7 m. Lake bed uncertainties for these retrievals are 0.05–0.20 m for ATM and 0.12–0.80 m for ICESat-2, with the highest uncertainties observed for lakes deeper than 4 m. The bimodal nature of lake returns means that high-confidence photons are often insufficient to fully profile lakes, so lower confidence and buffer photons are required to view the lake bed. Despite challenges in automation, the altimeter results are promising, and we expect them to serve as a benchmark for future studies of surface meltwater depths.
Highlights
The ice sheets of Antarctica and Greenland modulate rates of sea level rise, contributing 14.0 ± 2.0 mm (Antarctica) and 13.7 ± 1.1 mm (Greenland) since 1979 (Mouginot et al, 2019; Rignot et al, 2019)
We identify test cases from ICESat-2 and Airborne Topographic Mapper (ATM) altimetry data and use these pilot cases to develop an algorithm for detecting supraglacial lakes and retrieving lake depth
We present a method to detect supraglacial lakes and estimate lake depth from 532 nm laser altimetry data
Summary
The ice sheets of Antarctica and Greenland modulate rates of sea level rise, contributing 14.0 ± 2.0 mm (Antarctica) and 13.7 ± 1.1 mm (Greenland) since 1979 (Mouginot et al, 2019; Rignot et al, 2019). Meltwater plays vital roles in ice sheet evolution (e.g., van den Broeke et al, 2016), including aggregation on ice sheets as supraglacial lakes, many of which are several meters deep (Echelmeyer et al, 1991). When unfrozen, these lakes exhibit a lower albedo than that of the surrounding ice, allowing them to absorb more incoming solar radiation and melt ice more efficiently, generating a positive feedback (Curry et al, 1996).
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