11 Aug 2023
 | 11 Aug 2023
Status: this preprint is currently under review for the journal TC.

Evaluation of satellite methods for estimating supraglacial lake depth in southwest Greenland

Laura Melling, Amber Leeson, Malcolm McMillan, Jennifer Maddalena, Jade Bowling, Emily Glen, Louise Sandberg Sørensen, Mai Winstrup, and Rasmus Lørup Arildsen

Abstract. Supraglacial lakes form on the Greenland ice sheet in the melt season (May to October) when meltwater collects in surface depressions on the ice. Supraglacial lakes can act as a control on ice dynamics since, given a large enough volume of water and a favourable stress regime, hydrofracture of the lake can occur which enables water transfer from the ice surface to the bedrock where it can lubricate the base. The depth (and thus volume) of these lakes is typically estimated by applying a adiative transfer equation (RTE) to optical satellite imagery. This method can be used at scale across entire ice sheets but is poorly validated due to a paucity of in-situ depth data. Here we intercompare supraglacial lake depth detection by ArcticDEM digital elevation models, ICESat-2 photon refraction, and the RTE applied to Sentinel-2 images across five lakes in southwest Greenland. We found good agreement between the ArcticDEM and ICESat-2 approaches (Pearson’s r = 0.98) but found that the RTE overestimates lake depth by up to 153 % using the green band (543–578 nm) and underestimates lake depth by up to 63 % using the red band (650–680 nm). Parametric uncertainty in the RTE estimates is substantial and is dominated by uncertainty in estimates of reflectance at the lakebed which are derived empirically. Our analysis indicates that calculating depth with the RTE using literature-derived values for the parameters introduces significant uncertainty in the retrieval of depth information from optical imagery. Uncertainty in lake depth estimates translates into a poor understanding of total lake volume, which could mean that hydrofracture likelihood is under or over-estimated, in turn affecting ice velocity predictions. Further laboratory studies to constrain spectral radiance loss in the water column, and investigation of the potential effects of cryoconite on the estimation of lakebed reflectance could improve the RTE in its current format. However, we also suggest that future work should explore data-driven approaches to deriving lake depth from optical satellite imagery, which may improve depth estimates and will certainly result in better-constrained uncertainties.

Laura Melling et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on tc-2023-103', Anonymous Referee #1, 29 Aug 2023
  • RC2: 'Comment on tc-2023-103', Anonymous Referee #2, 24 Sep 2023

Laura Melling et al.

Laura Melling et al.


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Short summary
Lakes on glaciers hold large volumes of water which can drain through the ice, influencing estimates of sea level rise. To estimate water volume, we must calculate lake depth. We assessed the accuracy of three satellite-based depth detection methods on a study area in western Greenland and considered the implications for quantifying the volume of water within lakes. We found that the most popular method of detecting depth on the ice sheet scale has higher uncertainty than previously assumed.