Surface Roughness Prevents Radar Penetration of Some Martian Debris-Covered Glaciers

Buried ice in the Martian mid-latitudes is of high interest for In-Situ Resource Utilization (ISRU) by future crewed missions, as well as for its scientific value as a record of climate history on another planet. 'Lobate debris aprons,' widely considered to be debris-covered glaciers, constitute a large reservoir of such ice. Many have been probed by Mars Reconnaissance Orbiter's Shallow Radar (SHARAD) sounder, which imaged their base and constrained their internal composition to >80% water ice. The basal contact is not imaged by SHARAD for all aprons, however, which introduces the possibility that these features contain significantly less ice. In this study, we used SHARAD survey results in tandem with high-resolution digital terrain models to show that these 'non-detections' can be attributed to surface roughness, which through scattering reduces the coherent signal that penetrates the aprons. We quantified this effect using a fractal backscattering model and found that the roughest surfaces coincided with the location of basal non-detections. There is thus no need for reduced ice content to explain nondetection of lobate debris apron bases with SHARAD. This result leads us to interpret all lobate debris aprons as likely debris-covered glaciers, due to the similarities in their gross morphology and surface textures to aprons with basal detections.