Using ICESat-2 and Operation IceBridge altimetry for supraglacial lake depth retrievals

• Main Authors: Fair, Zachary, Flanner, Mark, Brunt, Kelly M., Fricker, Helen Amanda, Gardner, Alex S.
• Format: Text
• Language: English
• Published: 2020
• Subjects: Antarctic; Greenland; The Antarctic; Airborne Topographic Mapper; Antarc*; Antarctica; glacier
• Online Access: https://doi.org/10.5194/tc-2020-136; https://tc.copernicus.org/preprints/tc-2020-136/

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, but passive remote sensing techniques have inherent uncertainties associated with depth retrievals, and observations from the original ICESat mission experienced high absorption in water. 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 detect bottom returns for lake beds as deep as 7 m. 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. Using ICESat-2 confidence classifications of detected photons, we found that high-confidence photons are often insufficient to fully profile lakes, so lower confidence and buffer photons are recommended for improved retrievals. Despite issues in photon classification, the altimeter results are promising, and we expect them to serve as a benchmark for future studies of surface meltwater depths.