Interferometric swath processing of Cryosat data for glacial ice topography

摘要

We have derived digital elevation models (DEMs) over the western part of theDevon Ice Cap in Nunavut, Canada, using "swath processing" of interferometricdata collected by Cryosat between February 2011 and January 2012. With the standardESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) data product, the interferometric mode is used tomap the cross-track position and elevation of the"point-of-closest-approach" (POCA) in sloping glacial terrain. However, inthis work we explore the extent to which the phase of the returns in theintermediate L1b product can also be used to map the heights of time-delayedfootprints beyond the POCA. We show that there is a range of averagecross-track slopes (~ 0.5 to ~ 2°) for which the returns will be dominated by those beneath thesatellite in the main beam of the antenna so that the resultinginterferometric phase allows mapping of heights in the delayed range windowbeyond the POCA. In this way a swath of elevation data is mapped, allowingthe creation of DEMs from a sequence of L1b SARInCryosat data takes. Comparison of the Devon results with airborne scanninglaser data showed a mean difference of order 1 m with a standarddeviation of about 1 m. The limitations of swath processing, whichgenerates almost 2 orders of magnitude more data than traditional radaraltimetry, are explored through simulation, and the strengths and weaknessesof the technique are discussed.