Multi-frequency PolInSAR signatures of a subpolar glacier

Abstract

In recent years there has been increased interest in using SAR to study and monitor glaciers and ice sheets for glaciological and climate change research. This paper relates the complex interferometric coherence of land ice to an extinction coefficient and ground-to-volume scattering ratio, and validates this model with airborne PolInSAR data at L- and P-band collected using DLR's E-SAR system over the Austfonna ice cap in Svalbard, Norway. Observed coherences are compared with several PolInSAR scattering models including random volume (RV), random volume under ground (RVuG), oriented volume (OV) and oriented volume under ground (OVuG). In all cases the ice volume is approximated as an infinitely thick and uniformly lossy medium. Model predictions of interferometric coherence using estimated surface-to-volume scattering ratios and extinctions are validated against observed coherences referenced to corner reflectors deployed on the ice's surface. Measured and modelled phase centres were found to be in agreement within a few metres. The distribution of complex coherences on the unit circle suggests a possible oriented volume under ground (OVuG) scattering scenario for a significant portion of L-band PolInSAR observations in the ablation zone, although a limited observation space does not allow us to reach any firm conclusions regarding model suitability at P-band.