Validation of CryoSat-2 Elevation Measurements along the Greenland Inland Traverse

The Greenland Ice Sheet's sensitivity to climate change and potential contribution to sea-level rise make its mass balance of critical interest. Altimeter surveys of ice sheet elevation changes are a common method used to estimate changes in ice volume and mass balance. In-situ validation of CryoSat-2's measurements is key to assessing the satellite's performance. The 2011 Greenland Inland Traverse (GrIT) provides a detailed elevation profile across 1120km of the Greenland Ice Sheet. We compare GrIT Kinematic GPS elevations to remotely sensed elevation values from CryoSat-2's synthetic aperture interferometric radar altimeter (SIRAL). We examine CryoSat-2 measurement repeatability by comparing "crossover" points from ascending and descending satellite tracks. Overall CryoSat-2 crossover elevations agree, though some repeat measurements differ due to varying surface slope and facies conditions. Comparison of in-situ GPS data along the traverse with CryoSat-2 measured elevations reveals a small but constant vertical offset between GPS and CryoSat-2 elevation measurements. Comparing the mean GPS elevation within a single footprint reduces the offset. Calibrating CryoSat-2 elevations with GPS elevation measurements improves confidence in CryoSat-2 elevation values. Spatially extensive surface elevation measurements from CryoSat-2, validated with GrIT survey-grade GPS and combined with improved accumulation estimates, will reduce uncertainty in the mass balance of the Greenland Ice Sheet.