Measurement of Englacial Velocity Fields With Interferometric Radio Echo Sounders

Abstract

The surface velocity of ice sheets is now measured at high spatial and temporal resolutions by satellite-borne platforms. The availability of this data has enabled rapid progress in both monitoring the evolution of ice sheets and understanding their underlying physical processes. Because the material properties of ice are spatially variable and poorly constrained, however, it is difficult to infer englacial velocity fields from surface velocity alone. Radio echo sounders, also called ice-penetrating radars, can image beneath the surface and resolve englacial layering, commonly assumed to represent isochronal surfaces. In limited settings, interferometric measurements of these englacial layers have also been used to infer vertical velocity within ice sheets, however these applications to date have focused on areas where layers could be assumed to be flat. Here, we develop the mathematical relationships between observed englacial layer deformation and englacial velocity fields, making no assumptions about the shape of the layers and very minimal assumptions about the internal velocity structure. Taking this general approach opens up the possibility of using interferometric radio echo sounding to reconstruct three-dimensional englacial velocity fields at large scale across ice sheets. Potential applications of this method include data-driven estimation of ice rheology, inference of englacial conditions, and estimation of basal sliding. The proposed technique provides more direct constraints on these processes than has previously been available by remote sensing methods and offers the potential to both understand and predict the flow of ice sheets and glaciers.