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Ice Motion and Deformation in the SHEBA Region: Images, Data Sets, and Results from RADARSAT SAR |
Polar Science Center, Seattle
harry@apl.washington.edu
The Canadian RADARSAT satellite collected nearly 200 synthetic aperture radar (SAR) images of the SHEBA site between November 1, 1997, and October 8, 1998. The SHEBA Project Office ordered these images from the Alaska SAR Facility and will make sub-images available to SHEBA investigators in GIF format.
The images are geocoded to the SSM/I polar stereographic projection. Pixel values are calibrated radar backscatter. Two GIF sub-images have been created for each original image: (1) 40 x 40 km with 50m pixel size; (2) 200 x 200 km with 250m pixel size. All sub-images are centered on the SHEBA site.
The RADARSAT Geophysical Processor System (RGPS) used this series of SAR images to track a grid of points over the time intervals between successive images. The result is 184 ice motion files detailing the spatial pattern of ice motion on a 5 x 5 km grid over a 200 x 200 km area centered on the SHEBA site. Typical time intervals between successive images are one to three days. These data are available on the RGPS web site.
From the RGPS ice motion data, the SHEBA Project Office has computed the strain rate invariants (divergence, shear, vorticity) for all 184 time intervals and four different spatial scales: 50 x 50 km, 100 x 100 km, 150 x 150 km, and 200 x 200 km, all centered on the SHEBA site. These data are available on our web site.
Analysis of the ice deformation shows a clear distinction between winter and summer conditions, with sharp transitions between them. Winter is characterized by linear intersecting zones of high deformation (active cracks) separating plates of rigid ice. Summer is characterized by a more random pattern of deformation due to free drift and low ice strength.
The characterization of winter deformation in terms of cracks and plates allows the opening, ridging, and sliding of the pack ice to be computed and related to the deformation invariants. The large-scale invariants can also be related to the geostrophic wind, establishing a link between the large-scale continuous forcing and the small-scale discontinuous response.
For more information: http://psc.apl.washington.edu/Harry/Radarsat/.
