Radar Altimetry Simulation to Identify Sub-Footprint Ice-Sheet Surface Change

Satellite radar altimetry signals from glaciers and ice sheets represent a combination of scattering from ice-surface topography and the snow and firn volume. Changes in surface topography through time, even at sub-footprint scales, will change the interaction between the wavefront and surface, impacting the shape of the return waveform. Here, we describe a new facet-scattering model that uses arbitrary topographic inputs and can be used for testing hypotheses about ice-sheet surface change in the historical, three-decade-long pulse-limited radar altimetry record. We demonstrate the scattering model on both synthetic and real topographies, showing how off-nadir features and a deforming surface impact the returned waveform. We anticipate this simulator can be used to quantify sub-footprint surface change and the evolution of dynamic ice-sheet processes on rugged, high velocity ice streams and outlet glaciers in the decades before our modern, continuous laser altimetry and high-resolution stereophotogrammetric records capable of observing such changes began.