Retrieval of Snow or Ice Pack Thickness Variation Within a Footprint of Correlation Radiometers

Abstract

A new passive microwave remote sensing technique, wideband autocorrelation radiometry (WiBAR), directly measures the microwave propagation time difference of multipath microwave emission from low-loss layered surfaces such as a dry snowpack and a freshwater lake icepack. The microwave propagation time difference through the pack yields a measure of its vertical extent. However, the presence of variable pack thicknesses within a footprint of the radiometer’s antenna will add complexity to the retrieved time delay. This issue is more severe for WiBAR on airborne and spaceborne platforms than WiBAR on ground-based platforms since the footprint for a given radiometer antenna is larger. From a simple forward model for a layer having distinct thickness values within one footprint (pixel), the system requirements for resolving these distinct thickness values are derived. A subpixel lake ice thickness distinction of 3.7 cm is demonstrated with an X-band WiBAR instrument at an incidence angle of 70°.