Synthetic aperture radar interferometry over Rutford Ice Stream and Carlson Inlet, Antarctica

We describe the calibration and interpretation of interferograms generated from ERS-I synthetic aperture radar Single Look Complex (SAR. SLC) images of the Rutford Ice Stream area. Ground surveys provide over 100 tie-points with which to optimise the interferometric baselines that separate nominally repeated satellite orbits. Covariant tie-point errors are dealt with by constructing an error covariance matrix for the expected values of the unwrapped interferometric phases at the tie-points. With baseline parameters that minimise the weighted residual variance, rms tie-point residuals of less than I cm in slant range are obtained . These are attributed to a combination of interferometric phase noise, movement survey errors and inadequate slope information. The image set used is inadequate for isolating the influences of topography and movement, so the glaciological conclusions to be drawn are limited. Nevertheless, the interferograms confirm that the whole of the upper 50 k m of Carlson Inlet flows at a speed less than a tenth of that of the neighbouring Rutford Ice Stream. Also confirmed are the entry of faster-moving ice into the lower reaches of Carlson Inlet and the position of part of the Carlson Inlet grounding line. In general, the distribution of the residuals suggests no significant differences in ice movement between 1978 and 1992. An exception is the neighbourhood of the shear margin between Rutford Ice Stream and Carlson Inlet, where inconsistencies between ground surveys over the periods 1984-86 and 1994 -96 and interferograms from 1994 a n d 1996 suggest fluctuations in velocity of up to 10 m year-1.