Investigation of coastal dynamics of the Antarctic Ice Sheet using sequential Radarsat SAR images

摘要

Increasing human activities have brought about a global warming trend, and causeglobal sea level rise. Investigations of variations in coastal margins of Antarctica and inthe glacial dynamics of the Antarctic Ice Sheet provide useful diagnostic informationfor understanding and predicting sea level changes. This research investigates thecoastal dynamics of the Antarctic Ice Sheet in terms of changes in the coastal marginand ice flow velocities. The primary methods used in this research include imagesegmentation based coastline extraction and image matching based velocity derivation.The image segmentation based coastline extraction method uses a modifiedadaptive thresholding algorithm to derive a high-resolution, complete coastline ofAntarctica from 2000 orthorectified SAR images at the continental scale. This newcoastline is compared with the 1997 coastline also derived from orthorectified RadarsatSAR images, and the 1963 coastline derived from Argon Declassified IntelligenceSatellite Photographs for change detection analysis of the ice margins. The analysisresults indicate, in the past four decades, the Antarctic ice sheet experienced net retreatand its areal extent has been reduced significantly. Especially, the ice shelves andglaciers on the Antarctic Peninsula reveal a sustained retreating trend. In addition, the advance, retreat, and net change rates have been measured and inventoried for 200 iceshelves and glaciers.A multi-scale image matching algorithm is developed to track ice motion and tomeasure ice velocity for a number of sectors of the Antarctic coast based on 1997 and2000 SAR image pairs. The results demonstrate that a multi-scale image matchingalgorithm is much more efficient and accurate compared with the conventionalalgorithm. The velocity measurements from the image matching method have beencompared with those derived from InSAR techniques and those observed fromconventional ground surveys during 1970-1971. The comparison reveals that the icevelocity in the front part of the Amery Ice Shelf has increased by about 50-200 m/a.The rates of ice calving and temporal variation of ice flow pattern have been alsoanalyzed by integrating the ice margin change measurement with the ice flow velocityat the terminus of the outlet glacier.