Polarimetric Airborne Radar Sounding as an Approach to Characterizing Subglacial Röthlisberger Channels

Conventional airborne radar sounding techniques are well suited to the detection and characterization of flat-lying, specular subglacial water bodies. However, topographically positive, diffusively scattering Röthlisberger (R-) channels are more difficult to image, while also exerting substantial control on basal friction and ice dynamics. As subglacial R-channels share geometrical similarities with targets of interest in polarimetric ground-penetrating radar studies (i.e., cylindrical pipes), in this article, we investigate whether similar concepts can be adapted to detect and characterize R-channels. While closed-form analytical solutions exist for the scattering widths (SWs) of perfect electrically conducting and dielectric circular cylinders, the insight they provide for the polarimetric response of half-cylinder R-channels is limited. As such, a series of modeling experiments have been performed to characterize the SWs of half cylinders. Our results demonstrate that scattering from subglacial R-channels depends on numerous factors including the polarization and frequency of the incident radar wave, the size of the R-channel, and the relative orientation of the R-channel to a pair of orthogonally oriented, linearly polarized radar antennas. The results imply that patterns in the like-polarized echo powers across the signal bandwidth may be useful in inferring R-channel existence and possibly estimate R-channel size. However, as differences in SW are small and decrease with increasing misalignment between the acquisition system antennas and R-channel strike, achieving a high degree of radiometric resolution and stability should be a driving factor in polarimetric radar system design.