Ice Velocity Mapping Using TOPS SAR Data and Offset Tracking

Feature tracking and speckle tracking, are robust techniques to measure the velocity of glaciers and ice sheets. Displacement maps based on TOPS data may have small gaps if the bursts are not handled properly. Ice moving from one burst to a consecutive burst between two observations is not observed under the same squint angle, and hence speckle tracking is supposed to fail when cross-correlating consecutive bursts, whereas feature tracking provides the same result as when cross-correlating corresponding bursts. The size of the potential gaps depends on the ice displacement and the choice of Sentinel-1 product, as consecutive bursts overlap in the SLC product but not in the GRD product. An analysis of Sentinel-1 data from Greenland confirms the results expected from theory.