DInSAR and Coherence Tracking Applied to Glaciology: The Example of Shirase Glacier

Within the framework of a research project carried out in collaboration with the Department of Geography of the Vrije Universiteit Brussel (VUB), we have studied the contribution of Synthetic Aperture Radar (SAR) phasimetry in the field of glaciology. The main objective of this research was to extract surface velocity fields for the Shirase glacier, a fast-flowing continental ice stream in Draunning Maud Land, East Antarctica, by using differential SAR interferometry (DInSAR). Since the ice flow is mainly oriented along the azimuth direction, we developed a simple coherence tracking procedure which allows measuring azimuth displacements within a fraction of a pixel. Though less accurate than DInSAR range measurements, the velocity field calculated using this method is in accordance with velocities obtained by other methods. Introduction Several studies have shown that differential interferometry was particularly well suited for measuring ice stream displacement velocities along the range coordinate (Goldstein & al. 1993, Rignot 1996). When an observed point is displaced in the local horizontal plane between SAR acquisitions, the component of this movement along the slant-range direction generates a differential phase. Therefore, knowing the time lapse separating both acquisitions that are used to generate the interferogram containing a differential phase, one can calculate the mean velocity component along the slant-range direction. If the displacement has a component along the azimuth dimension, it has no influence on the differential phase. Therefore, DInSAR allows measuring only the slant-range component of a movement. This means that to measure a complete velocity field, one needs almost three interferometric pairs containing a differential phase, acquired along three different and non-coplanar incidences. Since they are based on ERS images, one can at most use ascending and descending passes, and a complete velocity field can only be inferred from differential interferometry imposing several restrictive hypotheses. Nevertheless, in the field of glaciology, remote sensing and, more particularly, SAR phasimetry is often a unique investigation method. The Shirase Glacier In this study, the area of interest is the central part of the Shirase glacier, located in Antarctica at 39° East and 70° South. We measured the displacement field of an ice stream covering an area approximately 20 km X 70 km. DInSAR and Coherence Tracking Applied to Glaciology: The Example of Shirase Glacier Dominique Derauw ([email protected]) Centre Spatial de Liège (CSL), Avenue du Pré Aily, B-4031 Angleur, Belgium To perform this study, we used three ERS Tandem pairs (Table 1). Acquisition Baseline Ambiguity dates Bx By B// B⊥ of altitude Pair 12 April 9 & 10, 1996 55.4 0.8 18.7 52.5 -171 Pair 34 May 14 & 15, 1996 61.7 -5.7 27.2 56.5 -158 Pair 56 June 2 &3, 1996 12.5 -2 12.6 -1.9 5588 Table 1: Available Tandem pairs