Ice velocity mapping of Ross Ice Shelf, Antarctica by matching surface undulations measured by ICESat laser altimetry

Abstract

We present a novel method for estimating the surface horizontal velocity on ice shelves using laser altimetry data from the Ice Cloud and land Elevation Satellite (ICESat;2003？2009). The method matches undulations measured at crossover points between successive campaigns. Elevation measurements are first relocated into a time-varying (moving) coordinate system using an initial velocity (e.g., from VELMAP), and then crossover height differences are minimized with an adjustment vector. Errors in geolocation of the ICESat tracks result in some error in the adjustment vectors, but these are small relative to the velocity adjustment for fast-moving ice shelves. We use the algorithm to estimate changes in the ice velocity of Ross Ice Shelf between an earlier mapping (from VELMAP) and the ICESat period. The new velocity field is compared with velocities from in situ measurements and satellite radar interferometry. The slowdown of 98 ± 34 m yr？1 (~ 23%) is observed in the ice shelf downstream of Whillans Ice Stream, and the deceleration rate is 3.1 ± 1.1 m yr？2 during last three decades. The method can be expanded to the simultaneous mapping of ice horizontal velocity, ice thickness change, and surface deformation for Antarctic ice shelves as well as a more accurate mapping using future ICESat-2 measurements.