Lake Level Change From Satellite Altimetry Over Seasonally Ice-Covered Lakes in the Mackenzie River Basin

Abstract

Variations in water levels of seasonally ice-covered subarctic lakes are indicators of environmental and climatic change. Satellite altimetry enables remote sensing of these lakes, but the lake phenology is problematic as radar reflection surfaces include water, snow, and ice. Reflection from multiple surfaces gives rise to two-peak waveforms across ice-covered lakes. Misinterpretation of the altimetric height has caused extracted water levels to be low compared with gauge data. In this study, a modified retracker is used to determine heights from the first altimetric subwaveform. Using <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> snow depth and ice thickness, the first reflection surface is shown to correspond closely to the snow/ice interface when the lake is frozen. The modified retracker is applied to the Great Bear Lake (GBL), Great Slave Lake (GSL), and Lake Athabasca (ATL) of the Mackenzie River Basin for the period 1992–2020. Standard deviations (Std) of differences between lake levels from Jason-2 waveforms and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> data across GBL and GSL are 0.06 m with the new methodology compared with 0.11 and 0.08 m, respectively, using the standard Ice retracker. With an Std of 0.11 m between altimetric and gauge lake levels, TOPEX/Poseidon is less accurate than the combined Jason missions (Std: 0.07 m).