Synthetic aperture radar interferotnetry over Rutford Ice Streatn and Carlson Inlet, Antarctica

We d escribe the calibration and interpretation of interferograms generated from ERS-I synthetic ape rture rad a r Single Loo k Complex (SAR .SLC) images of the Rutford Ice Stream a rea. Ground surveys provide over 100 tie-points with which to optimise the interferometric baselines that sepa rate nominall y repeated satellite orbits. Covariant tie-point errors are dealt with by constructi ng an error covariance matrix for the expected values o f the unwrapped interferometric phases at the tie-points. With baseline pa rameters tha t minimise the weighted res idua l var ia nce, rms ti e-point residua ls of less than I cm in sla nt range are obtained . These a re a LLributed to a combi na tion of in terferometric phase noise, movement survey errors and inadequate lope information. The image set used is inadequate for isolating the influences of topography and movement, . 0 the glaciologieal conclusions to be drawn are limited . Nevertheless, th e interferograms confirm that the whole of the upper 50 km of Carl so n Inlet flows at a sp eed less than a tenth of that of the neighbouring Rutford Ice Stream. A lso confi rmed are the entry of fas ter-moving ice into the lower reaches of Carlson Inl et a nd the position of part of the Carlson Inlet grounding line. In general, the distributio n of the residua ls suggests no significant differences in ice movement between 1978 a nd 1992. An exceptio n is the neighbourhood of the shear margin between Rutford Ice Stream and Carl son Inlet, where inconsistenci es between ground surveys over the periods 198486 and 199496 and interferograms from 1994 a nd 1996 suggest fluctuations in veloc ity of up to 10 m year 1