Potential Application of Terrasar-X Satellite Data for Discriminating Age of Drained Thermokarst Lake Basins on the Seward Peninsula, Alaska

Drained thermokarst lake basins (DTLBs) are important indicators of permafrost and thermokarst lake dynamics in polar lowlands with ice-rich permafrost. They accumulate significant amounts of soil organic carbon in the form of peat which is of interest to understanding climate change feedbacks with thermokarst dynamics. However, understanding the temporal and spatial dynamics of DTLBs requires substantial geological, cryolithological, and geochronological ground work in remote regions. Application of remote sensing methods to map DTLBs and their properties is a critical component in upscaling such field results to larger regions. Previous studies have demonstrated potential use of optical remote sensing data to map DTLBs as well as classify their relative age relying on relationships of land surface properties to post drainage succession in vegetation, soils, and permafrost aggradation. In this study, we tested the application of X-band Synthetic Aperture Radar (SAR) data of the German TerraSAR-X satellite with 3 m spatial resolution for determining the time since lake drainage (or drained basin age) for a set of DTLBs located in the ice-rich permafrost region of the northern Seward Peninsula, Alaska. Six stripmap HH polarization images covering the study region of approx. 3801 sq. km were acquired at different dates within the growing season period (July - September) of 2009. A Landsat-5 TM image acquired in July 2009 was also used to aid in the understanding of vegetation patterns in drained basins. We used a set of radiocarbon-dated peat cores from 14 basins ranging in age from 250 to 9000 years before present as well as 57 basins that were observed draining with aerial and satellite image time series within the recent decades to compare TerraSAR-X data with basin age. First for the set of young basins, results show that it is not possible to discriminate the age of DTLBs that drained recently within the last 50 to 60 years by using X-band SAR. However, it was possible to observe seasonal dynamics in these young DTLBs, reflected as increase in backscatter, as the growing season progressed from July to September. For the older DTLBs dated with radiocarbon, a significant logarithmic relationship between basin age and TerraSAR-X backscatter and basin age and Landat-5 TM based Normalized Difference Vegetation Index (NDVI) was observed. The log curves show decreasing trend of backscatter and NDVI as basin age increases. Overall, TerraSAR-X results show the potential application of X-band microwave data to map long-term succession dynamics of DTLBs, which are characterized by post-drainage changes in vegetation, hydrological characteristics, permafrost aggradation, ground ice accumulation, and localized frost heave.