Impacts of differing melt regimes on satellite radar waveforms and elevation retrievals

Abstract

Geodetic surface mass balance calculations rely on satellite radar altimeters such as CryoSat-2 to understand elevation and volumetric changes of the Greenland Ice Sheet (GrIS). However, the impact of varying GrIS shallow subsurface stratigraphic conditions on level 2 CryoSat-2 elevation products is poorly understood. We investigate the reliability of the Offset Center Of Gravity (OCOG) and University College London Land-Ice (ULI) elevation retracking algorithms through the analysis of (and comparison with) level 1B waveform-derived leading-edge width (LeW). We generate a 2010 to 2021 LeW time series using temporal clustering and Bayesian model averaging, and we compare them with level 2 OCOG and ULI elevation time series. We perform this workflow at Summit Station, North Greenland Eemian Ice Drilling (NEEM) Camp, and Raven Camp, chosen to represent the upper and lower bounds of the dry-snow zone and percolation zone. We note that melting event, snowpack recovery, and potentially anomalous snow accumulation and high-speed wind signatures are evident in Summit Station's LeW time series. We find that level 1B LeW has a significant inverse relationship with the ULI level 2 elevations at NEEM Camp and Summit Station and likely with the entire dry-snow zone. The ULI retracked level 2 elevations at Raven Camp (and likely the entire percolation zone) have no clear elevation bias associated with significant melt events. The OCOG retracked level 2 elevations showed no significant association with LeW at any site. Future work is needed to understand the impacts of GrIS high-speed wind events and snow accumulation on elevation products.