Validation of grounding line of the East Antarctic Ice Sheet derived by ERS-1/2 interferometric SAR data

摘要

We applied Synthetic Aperture Radar (SAR) Interferometry (InSAR) in the East Antarctic marginal ice zone between 25°W and 40°E . ERS-1/2 tandem data received at Syowa Station in 1996 were mainly used. ERS interferograms with range-azimuth coordinates were transformed into World Geodetic System 1984 (WGS84) coordinates. For this transform, we used the RAMP (RADARSAT Antarctic Mapping Project) image which is already defined by the WGS84 reference system. Significant features in the ERS intensity image show similar textures to those in the RAMP image. By taking the above features in the ERS intensity image as ground control points of known WGS84 geodetic coordinates from the RAMP image, we assigned WGS84 coordinate values to any element in the ERS scene by a least-squares fitting with a second-order polynomial function. It is noted that the ERS InSAR scene has the same WGS84 coordinate system as the ERS intensity scene. We extracted and digitized grounding lines from the ERS InSAR scene as a curve of steeply changing fringe pattern at the ocean-continent boundary. Features of the grounding line in the Antarctic Digital Database (ADD) were monotonous as interpreted from blurring of the Landsat image on the ice shelf and the ice sheet. In contrast, InSAR-derived grounding lines delineated complex features as a result of ocean tidal motion at the ocean-continent boundary. For example, the ADD shows a peninsula around 15°E , but it actually is a group of snow-covered islands or ice rises. The positional discrepancy of the ADD grounding line from the InSAR-derived grounding line reaches 5000m around Riiser-Larsenhalvya, and about 1200m around Padda and Skallen.