Interferometric swath processing of Cryosat data for glacial ice topography

Abstract

Abstract. We have derived digital elevation models (DEMs) over the western part of the Devon Ice Cap in Nunavut, Canada, using "swath processing" of interferometric data collected by Cryosat between February 2011 and January 2012. With the standard ESA (European Space Agency) SARIn (synthetic aperture radar interferometry) level 2 (L2) data product, the interferometric mode is used to map the cross-track position and elevation of the "point-of-closestapproach" (POCA) in sloping glacial terrain. However, in this work we explore the extent to which the phase of the returns in the intermediate L1b product can also be used to map the heights of time-delayed footprints beyond the POCA. We show that there is a range of average cross-track slopes (∼ 0.5 to ∼ 2 • ) for which the returns will be dominated by those beneath the satellite in the main beam of the antenna so that the resulting interferometric phase allows mapping of heights in the delayed range window beyond the POCA. In this way a swath of elevation data is mapped, allowing the creation of DEMs from a sequence of L1b SARIn Cryosat data takes. Comparison of the Devon results with airborne scanning laser data showed a mean difference of order 1 m with a standard deviation of about 1 m. The limitations of swath processing, which generates almost 2 orders of magnitude more data than traditional radar altimetry, are explored through simulation, and the strengths and weaknesses of the technique are discussed.

Joint inversion estimate of regional glacial isostatic adjustment in Antarctica considering a lateral varying Earth structure (ESA STSE Project REGINA)

“…One reason is the sampling problem, which was partially alleviated by combining ICESat (high accuracy in coastal regions) and Envisat (smaller bias in central Antarctica). Our results show that further improvement is expected with CryoSat-2, particularly with its SARIn mode in coastal areas and possible swath processing, which provides denser elevation rate coverage around the ice margins where the largest rates are occurring (Gray et al 2013). Here, however, we refrain from including the CryoSat-2 data in the inversion, because the time span of the data set was insufficient to retrieve [42] annual rates of surface-elevation change comparable to the other data set.…”

Surface elevation change and mass balance of Icelandic ice caps derived from swath mode CryoSat‐2 altimetry

“…We measure time-dependent elevation over the ice caps by using swath processing of CS2 level 1b SARIn data (SwSARIn). In contrast to the conventional POCA method, SwSARIn exploits the full radar waveform to provide a dense swath of elevation measurements across the satellite ground track (beyond POCA) when signal and surface conditions are favorable (see the supporting information) [Hawley et al, 2009;Gray et al, 2013;Christie et al, 2016;Ignéczi et al, 2016]. As a reference, we also use elevations derived from the operational CS2 level 2 POCA product to assess ice cap elevation changes (see the supporting information), where POCA refers to the CS2 heights obtained via conventional retracking [Wingham et al, 2006].…”

Assessment of CryoSat-2 interferometric and non-interferometric SAR altimetry over ice sheets

“…Finally, it is worth reiterating that here we have focused on inter-comparing existing L2 data. Clearly there are also other benefits to an interferometric system, such as the improved data density that can be achieved by utilizing swath processing (Hawley et al, 2009;Gray et al, 2013).…”