Abstract
In recent years, the Sentinel-1 satellites have provided a data archive of unprecedented volume, delivering C-band Synthetic Aperture Radar (SAR) acquisitions over most of the polar ice sheets with a repeat-pass period of 6–12 days using Interferometric Wide swath (IW) imagery acquired in Terrain Observation by Progressive Scans (TOPS) mode. Due to the added complexity of TOPS-mode interferometric processing, however, Sentinel-1 ice velocity measurements currently rely exclusively on amplitude offset tracking, which generates measurements of substantially lower accuracy and spatial resolution than would be possible with Differential SAR Interferometry (DInSAR). The main difficulty associated with TOPS interferometry lies in the spatially variable azimuth phase contribution arising from along-track motion within the scene. We present a Sentinel-1 interferometric processing chain, which reduces the azimuth coupling to the line-of-sight phase signal through a spatially adaptive coregistration refinement incorporating azimuth velocity measurements. The latter are based on available ice velocity mosaics, optionally supplemented by Burst-Overlap Multi-Aperture Interferometry. The DInSAR processing chain is demonstrated for a large drainage basin in Northeast Greenland, encompassing the Northeast Greenland Ice Stream (NEGIS), and integrated with state-of-the-art offset tracking measurements. In the ice sheet interior, the combined DInSAR and offset tracking ice velocity product provides a spatial resolution of 50 × 50 m and 1-sigma accuracies of 0.18 and 0.44 m/y in the x and y components respectively, compared to GPS.
Highlights
Ice velocity is an essential parameter in the study of ice sheet and glacier dynamics
We demonstrate the feasibility of generating Sentinel-1 Terrain Observation by Progressive Scans (TOPS) Differential SAR interferometry (DInSAR) ice velocity measurements in the interior of the Greenland ice sheet using a DInSAR processing approach based on an azimuth coregistration refinement, as in [17]
The contribution of this study is to demonstrate how the Sentinel-1 TOPS data archive can be further exploited by applying DInSAR processing in ice velocity retrieval
Summary
Ice velocity is an essential parameter in the study of ice sheet and glacier dynamics. Offset tracking has the advantage of producing two-dimensional velocity measurements, namely along the range (satellite line-of-sight) and azimuth (flight path) dimensions, and is applicable even on fast-flowing outlet glaciers, which may reach velocities as high as several km/year. The accuracy and resolution of the amplitude-based offset tracking velocity retrievals, are generally substantially poorer than those obtained with DInSAR [6], the latter technique provides only measurements of the range motion component. A comprehensive review of SAR-based ice velocity measurement techniques applicable to Stripmap imagery is provided in [6]
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