Bed topography under Greenland outlet glaciers revealed by Operation IceBridge data and mass conservation

Detailed maps of bed elevation and ice thickness are essential to many glaciological applications, including ice sheet numerical models. These maps are typically obtained using airborne radar-sounding profiler data interpolated onto regular grids using geostatistical techniques, such as kriging. While this approach provides continuous maps of bedrock elevation, it generates products that are not consistent with ice flow dynamics and are impractical for high-resolution ice flow simulations. Here, we first analyze radar-sounding data from a dense survey of Russell Glacier, in central-west Greenland, collected in 2010 and 2011 by NASA's Operation IceBridge. We compare gridded maps of bed elevation obtained using (1) radar tomography, (2) ordinary kriging and (3) mass conversation. Radar tomography eliminates radar-sounding profiler errors caused by off-nadir bed reflections to yield reference bed elevations. Ordinary kriging yields a standard error of 50 m at 500 m resolution, but with model artifacts in between tracks and flux divergence errors larger than 200 m/yr, which confound ice sheet flow models. Mass conservation optimally combines radar-sounding profiler data with independently gridded ice velocity data to lower the standard error to 30 m and flux divergence errors smaller than 1 m/yr. More importantly, mass conservation uniquely reveals complex structural features in bed elevation, e.g. valleys, ridges, bumps and hollows, that play a central role in channelizing ice flow toward the ice sheet margin. We then apply this technique to other outlet glaciers along the west coast of Greenland. The application of the mass conservation method to the entire ice sheet periphery, combined with radar tomography, promises to be transformative in our knowledge of basal topography in coastal Greenland, especially for the modeling of its outlet glaciers. This work was performed at the University of California Irvine and the California Institute of Technology's Jet Propulsion Laboratory under a contract with the National Aeronautics and Space Administration, Cryospheric Sciences Program, grant NNX12AB86G.ed topography (m) of Russell Glacier inferred using the mass conservation method at 400 m resolution. The dashed white line defines the limits of the model domain. NASA Operation IceBridge (OIB) flight tracks are indicated as lines. Surface elevation is from Howat et al. 2012 (in prep.), including on ice-free zone. Note the agreement between ice-free and ice-covered elevations.