Monitoring Six Decades of Thermokarst Change in the Barrow Region, Alaska, Using Remote Sensing Data

Barrow, the northern most city of the United States, lies in the continuous permafrost region of the Arctic Coastal Plains. It witnesses long, dry, very cold winters and short, moist, cool summers. The continuous permafrost in this region is about 400 m thick, and the active layer of the permafrost that thaws every summer and refreezes in winter is about 25-100 cm thick. The coastal tundra at Barrow has low relief and is dominated by a pattern of ice-wedge polygons, shallow oriented lakes, drained lake basins and small ponds. The lakes are oriented and elongated possible as a result of differential erosion at their north and south ends. Because of the very low relief and the underlying permafrost, drainage is poor and stream channels meander widely. Available high resolution aerial photos and satellite images from the months of July and August for the Barrow area were processed to map primarily the ice wedge polygons and monitor their decadal change. These data sets included aerial photo mosaics from 1948, 1955, 1979, 1984, and 1997; and a Quickbird Panchromatic satellite image from 2002. Image pre-processing involved `image-to-image georeferencing' using the latest Quickbird image as the master image. Polygons and ponds were mapped on the individual images using manual onscreen digitization technique. These vector layers of polygons and ponds for different date images were then overlayed in a GIS environment and analyzed for changes in shape and size. Fieldwork carried out in the summer of 2005 involved differential GPS measurement to precisely map the extent of the selected polygons and ponds. Cross sectional depth measurements were made for selected ponds to serve as baseline data for future measurements and monitoring efforts. Field observations were used for validation of remote sensing interpretation. Results show some significant changes in the study area which have been attributed to both human and natural causes. In some cases it is difficult to conclude whether the changes observed are due to larger climatic changes in the region or due to seasonal change patterns.