Polarimetric SAR modelling of a two-layer structure: A case study based on subarctic lakes

Abstract

The work contributes to the interpretation of quad polarimetric SAR data over (shallow) subarctic lakes, on the purpose of investigating SAR capabilities in revealing facts about the subsurface and the inhomogeneities within the ice layer which are dominated mainly by methane bubbles. For this, a model for the polarimetric backscattering from a two-layer structure observed by a fully polarimetric side looking synthetic aperture radar at low frequency (L-Band) is developed. The upper layer thickness is few metres thick and contains inhomogeneities. The developed model describes the backscattering as the incoherent sum of the three main contributions: subsurface (X-Bragg), volume and dihedral backscattering. The volume is modelled as a cloud of partially vertically oriented ellipsoids. The dihedral backscattering component is modelled as the electromagnetic wave reflected on the subsurface after being scattered by the same cloud of particles that is responsible for the volume backscattering. The mathematical formulation of this dihedral backscattering is presented for the first time here and proved to be an essential component in the model. The model simulations are compared to data obtained by ALOS-PALSAR over frozen shallow subarctic lakes acquired over several regions in the northern wetlands. ALOS data show the same polarimetric backscattered signature as the simulations. The model can describe temporal changes of the ice and the difference between grounded and floating ice.