Radar images of the bed of the Greenland Ice Sheet

Abstract

[1] In this paper, we apply radar tomography methods to very-high-frequency, airborne synthetic-aperture radar data to measure the ice thickness field and to construct three-dimensional basal image maps of a 5 × 20 km study area located along the southern flank of the Jakobshavn Glacier, Greenland. Unlike ice radar measurements typically made at nadir, our approach uses radar-echo phase and amplitude measured across an antenna array to determine the propagation angle and signal strength of pixel elements distributed on each side of the aircraft flight path. That information, combined with knowledge of aircraft position and the assumed dielectric properties of the glacier, can be used to measure ice thickness and radar reflectivity across a 3-km wide swath. Combining ice thickness and surface topography data, we estimate basal topography and basal drag. We conclude that the glacier is sliding over the bed. We use the three-dimensional image maps of the bed to inspect the modern subglacial geomorphology and find for the first time beneath the Greenland Ice Sheet assemblages of long ridge-groove landforms that are oriented in the direction of the ice flow. Spatial dimensions (10 to 30 m depths, 150 to 500 m spacing and lengths of 10 km or more) and correlation with the current ice flow direction suggest that these are glacial erosional features similar to mega-grooves observed on deglaciated terrain.