HR: 1340h
AN: C13A-0263    [Abstracts]
TI: Synthetic Aperture Radar Remote Sensing of Bottom-Fast ice in the Mackenzie Delta Region, Northwest Territories, Canada
AU: * Solomon, S M
EM: ssolomon@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 1006, Dartmouth, NS B2Y 4A2 Canada
AU: Manson, G
EM: gmanson@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 1006, Dartmouth, NS B2Y 4A2 Canada
AU: Fraser, P
EM: pfraser@nrcan.gc.ca
AF: Natural Resources Canada, PO Box 1006, Dartmouth, NS B2Y 4A2 Canada
AB: Bottom-fast ice (BFI) refers to sea- or lake-ice that freezes to the sea- or lake-bed during the course of the winter season. The timing and distribution of BFI controls the mean annual temperature of the upper sediment column and therefore the potential for development and maintenance of permafrost and the thickness of the sub-bottom active layer. Air- and satellite-borne Synthetic Aperture Radar (SAR) imagery has been used to identify and map the distribution of BFI in Alaskan lakes and more recently in the nearshore of the Laptev Sea. It has been demonstrated that relatively high backscatter of SAR signals in lacustrine environments is caused by a combination of a strong reflection from the ice-water interface and scattering by tubular bubble inclusions within the ice. Lower backscatter regions are found where ice is frozen to the bed and the SAR signal passes into and is absorbed by the soil beneath. Some estuarine environments (e.g. the Lena Delta-Laptev Sea) are characterised by sufficiently freshwater in the shallow nearshore that the SAR signal should behave in the same manner. This paper describes the application of these concepts to the lakes of the Mackenzie Delta and the adjacent uplands and along the Beaufort Sea coastline. Bathymetric data from lakes, ice thickness measurements, and interpretation of ground-penetrating radar (GPR) are used to validate the interpretations from SAR imagery. Regions of low SAR backscatter are associated with mapped shallow water in lakes and the nearshore regions of the Mackenzie Delta. Relatively higher backscatter is found in deeper areas. The maximum extent of low SAR backscatter occurs in April and is associated with regions of the sea and lake bed that are generally less than 1.5 m water depth. Interpretations of SAR imagery become problematic in May and June because of the presence of a wet snowpack and flood or meltwater on the surfaces of the ice. A time series of RADARSAT ScanSAR Narrow and fine mode images is used to monitor the growth of these low backscatter zones beginning with inception around subaerial shoals in November and culminating in extensive regions by April. Differences between interpretations of BFI extent based on RADARSAT and GPR suggests that the former may be more sensitive to areas that are either marginally bottom-fast or potentially subject to tidal influences (i.e. periodic lift-off from the seabed). Additional validation of the technique in the shallow coastal estuarine environment is presently underway.
DE: 4275 Remote sensing and electromagnetic processes (0689)
DE: 3020 Littoral processes
DE: 3022 Marine sediments--processes and transport
DE: 1640 Remote sensing
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting