A Study of Polarimetric Parameters Used for Sea Ice Classification

Abstract

The Arctic region of the Earth are largely covered by sea ice, which is important for the marine ecosystems locally in the region, but it also has an impact on the climate systems. Recent climate changes means that the sea ice is melting and the coverage is shrinking which can have a global impact. Monitoring these sea ice changes are important to get an understanding of this impact. There are multiple options for how to carry out this monitoring, but the Arctic is a cold, dark and remote region, so a good option is using satellite images. A special advantage of using SAR (Synthetic Aperture Radar) satellites is that they are insensitive to weather conditions and darkness, which can be a challenge in the Arctic regions, especially during the winter months. Today operational ice services produces sea ice charts using such SAR images but they primarily reply on dual-polarimetric data. These images covers large areas due to the large swath for these modes and are idea for a Pan-Arctic coverage. However, they are impacted by e.g., effects of varying incidence angle throughout the images. This thesis will study the possibilities that lies within radar polarimetry, a field that utilized fully polarimetric data to extract even more information regarding the target on the surface, in this case sea ice. Moreover, these images enabled extraction of scattering type information and through this added information improve the sea ice type classification maps. The images studied here are two sets of fully polarimetric RADARSAT-2 data that covers the same sea ice but with varying incidence angles. Four different polarimetric features; the co-polarization ratio, the M-parameter, degree of polarization as well as the polarimetric coherence, were investigated for their separability measures between different sea ice types as well as how affected they are by incidence angle variations. Out of these four the co-polarization ratio was found to be useful to separate the thinner sea ice types as well as open water from the surrounding thicker sea ice. Both the M-parameter and the degree of polarization showed promise in separating deformed sea ice from the other ice types at higher incidence angles. Though limited consistent separability between different ice types were observed for the polarimetric coherence. The polarimetric coherence was found to be independent on the incidence angle, though the other three parameters showed an incidence angle dependency.