Discontinuous glacier motion as a test case for improving the accuracy of high resolution InSAR and SAR offset tracking methods

Abstract:

The brittle failure of glacier ice results in discontinuous glacier motion (e.g. crevasse formation, thrust faulting) characterized by spatially discontinuous velocity fields. Understanding the forms and mechanisms of discontinuous glacier motion is inhibited, in large part, by a lack of observational evidence, a gap that SAR remote sensing may be able to fill. When attempting to capture discontinuous or highly spatially variable motion fields with older sensors, InSAR offset methods are plagued by ambiguity and SAR offset methods by coarse resolution. However, some modern SAR sensors possess the high spatial resolution in azimuth necessary to resolve many forms of discontinuous glacier motion by combining InSAR with offset tracking via local coherence optimization techniques. This approach, however, still relies on SAR offset tracking methods which suffer from false matches that result in discontinuities in the measured displacement field that appear similar to the displacement fields caused by actual discontinuous motion. As such, discontinuous glacier motion provides an excellent test case for, and potential demonstration of, optimized offset tracking methods that reduce the prevalence of false matches and produce offset maps of very high accuracy that can be used to refine InSAR offset tracking products. We investigate the causes of false matches that occur during offset tracking and aim to develop methods for detecting and reducing the frequency of these false matches. Accuracy gains of the optimized method are quantified using synthetic SAR data. The methods are tested on RADARSAT-2 spotlight mode data collected over the Expedition Fjord glaciers on Axel Heiberg Island in the Canadian High Arctic, where previous in-situ and SAR-related work shows evidence of discontinuous glacier motion. The optimized methods are expected to provide new observational evidence of discontinuous glacier motion and its characteristics, while generally increasing the accuracy of offset tracking products such as glacier displacement maps.