Measurements of Sea Ice Thickness using Polarimetric Radar Systems

Abstract

This thesis presents an overview of the interactions between microwaves and physical properties of sea ice and snow, such as the dielectric constant and surface roughness, in order to successfully measure sea ice thickness from polarimetric radar systems. Using a ground-based scatterometer system and various microwave scattering models, polarimetric backscattered signatures from sea ice and snow were investigated as evidence of the evolution of the physical properties during the freezing and melting seasons. Based on these results, the optimum method for measuring the thickness of sea ice covered with snow using polarimetric SAR data was explored via numerical simulations and experimental measurements. Experiments conducted using the ground-based scatterometer system as well as the in-situ measurements showed that most of the polarimetric signatures (C-band) with relatively high incidence angles (i.e., about 40°) can be backscattered from the interface between snow cover on sea ice and the surface of the sea ice over the freezing season. Microwaves can penetrate the snow cover during this season owing to the lower dielectric properties of the snow cover (about 1.25). Conversely, the signatures were predominantly backscattered from the surface of the snow cover during the melting season due to high dielectric properties induced by surface melting water. For the freezing season, the in-situ measurements and numerical simulations showed that the number of polarimetric signatures backscattered within the sea ice volume can increase with sea ice growth due to evolutions of the dielectric properties induced by the desalination process, and the surface roughness of sea ice can increase with sea ice growth due to superimposed and ridging processes. Based on these observations, the relationship between the depolarization effects of polarimetric signatures (C- and X-band) and sea ice thickness was investigated using various numerical simulations and a case study. A strong correlation was found between the in-situ sea ice thickness and the SAR-derived depolarization factors (i.e., the co-polarized correlation and cross-polarized ratio). These results clearly demonstrate a one-to-one relationship between the thickness and the depolarization factors, which further suggests that the depolarization factors could be effective parameters in measuring the thickness of snow-covered sea ice with space-borne polarimetric SAR data