An assessment of satellite-derived supraglacial lake depth measurements on the Greenland ice sheet

Supraglacial lakes (SGLs) form when meltwater collects in glacial surface depressions. On the Greenland ice sheet (GrIS), SGL position is controlled by bedrock topography, meaning SGLs form in approximately the same locations each melt season. SGLs provide surface water storage and mediate the transfer of surface water to the ice sheet bed. Drainage water from SGLs has been shown to infiltrate to the base of the ice sheet and lubricate the ice sheet-bedrock interface, causing transient increases in basal sliding at the glacier margin. SGL depth is used to calculate the volume of water contained within the basin and thus the likelihood of hydrofracture caused by increased pressure from overlying water. As overlying water pressure is a function of water depth, determining the accuracy of depth estimation techniques is of the utmost importance in obtaining reliable estimates of hydrofracture likelihood and in determining SGL drainage impacts on ice sheet velocity.

Here, we present the results of an intercomparison of SGL depth measurements focused on the Watson River region of the GrIS. Previous studies have derived SGL depth by applying the Philpot (1989) radiative transfer equation to satellite-derived optical imagery. These results proved difficult to validate until recent advancements in remote sensing which allowed us to compare the radiative transfer-derived depths to laser altimetry measurements and high-resolution digital elevation modelling. Previous research has separately investigated the use of the Philpot (1989) radiative transfer equation, laser altimetry and digital elevation models, but none have intercompared all three.

This research compares estimates of SGL depths in the Watson River region in southwest Greenland that have been derived using three satellite-based approaches; 1) by applying the radiative transfer equation proposed by Philpot (1989) to Sentinel-2 optical satellite imagery, 2) using ICESat-2 laser altimetry and 3) from ArcticDEM digital elevation models.

Using the radiative transfer equation, we find the green band overestimates SGL depth and the red band underestimates SGL depth (with caveats) compared to ICESat-2 transects and digital elevation models. In summary, we achieve the first comprehensive intercomparison of these methods and provide insight into the strengths and potential limitations of each method, including levels of agreement between datasets, and associated uncertainties. This work helps to improve confidence in radiative transfer-derived estimates of SGL depth and volume and, consequently, quantitative estimates of meltwater storage on the surface of the GrIS. This research is associated with ESA’s Polar+ 4DGreenland study.