Perspective Back-Projection Algorithm: Interface Imaging for Airborne Ice Detection

The deployment of traditional ground-penetrating radar (GPR) systems for ice detection on steep terrain presents substantial safety challenges for ground crews due to inaccessi-bility and hazardous working conditions. However, airborne GPR (AGPR) and radio echo sounding (RES) provide solutions for these difficulties. Assuming ice is homogeneous, we introduce a perspective back-projection algorithm designed to process AGPR or RES data that directly searches for unobstructed refracted electromagnetic (EM) wave paths and fo-cusing EM energy below the surface by computing path-specific travel times. Our results from 2-D and 3-D imaging tests indicate that the perspective back-projection algorithm can accurately image the ice-rock interface. However, Snell's Law suggests that part of the energy may fail to propagate through the air-ice interface and reach either the ice-rock in-terface or the receivers in scenarios where the incident angle of an EM wave exceeds a cer-tain threshold. This energy deficit can hinder the perspective back-projection algorithm from accurately imaging such ice-rock interfaces. Despite these limitations, the perspective back-projection algorithm remains a promising tool for imaging sub-ice interfaces in AGPR and RES ice detection.