Cryospheric and Polar Processes Seminar: Kevin Schaefer

Using Interferometric Synthetic Apaerature Radar (InSAR) to Remotely Sense Active Layer Thickness in Permafrost Regions

by Dr. Kevin Schaefer - Research Scientist, NSIDC/CIRES

Active layer thickness (ALT) is a critical parameter for monitoring the status of permafrost, typically measured at specific locations using probing, in situ temperature sensors, or other ground-based observations. The Circumpolar Active Layer Monitoring (CALM) network has conducted ALT measurements over the past two decades, but is under-populated and sparse. Here we describe the Remotely Sensed Active Layer Thickness (ReSALT) product to remotely sense active layer thickness. We use the Interferometric Synthetic Aperture Radar (InSAR) technique to 1) measure long-term subsidence trends resulting from the melting and subsequent drainage of excess ground ice in permafrost, and 2) measure seasonal subsidence resulting from the expansion of soil water into ice as the active layer freezes and thaws. We estimate ALT from the seasonal subsidence assuming a vertical profile of water within the soil column and identify individual thermokarst features as spatial anomalies in the subsidence trends. We present 100x100 km2, 100 m resolution ReSALT products for several sites on the North Slope of Alaska: Prudhoe Bay, Barrow, Toolik Lake, Happy Valley, and the Anaktuvik fire zone. We validated ReSALT using in situ measurements of ALT from CALM and Ground Penetrating Radar. ReSALT has proven effective in measuring local variations in ALT and thermokarst activity on the North Slope of Alaska with broader potential applications across the permafrost regions of North America and Eurasia.