Analyzing intra-seasonal dynamics of ice-rich permafrost degradation in the Lena Delta using TerraSAR-X backscatter time-series

• Main Authors: Stettner, Samuel, Lantuit, Hugues, Heim, Birgit, Bartsch, Annett, Widhalm, Barbara
• Format: Conference Object
• Language: unknown
• Published: 2015
• Subjects: Arctic; Herschel Island; Yukon; Herschel; Ice; lena delta; permafrost; Tundra
• Online Access: https://epic.awi.de/id/eprint/41198/; https://epic.awi.de/id/eprint/41198/1/2015_ArcticNet_poster_stettner.pdf; https://hdl.handle.net/10013/epic.48149; https://hdl.handle.net/10013/epic.48149.d001

Arctic warming is leading to substantial changes of Arctic environments, such as the rapid degradation of ice- and organic-rich permafrost coasts and riverbanks. Reactivation of these ancient carbon pools and the release of carbon to the atmosphere could further accelerate climate warming. Short and long term annual retreat rates of permafrost coasts and riverbanks are mostly based on optical aerial and satellite imagery. However, in the Arctic cloud coverage often limits the use of optical remote sensing. Synthetic aperture radar (SAR) systems operate unaffected by atmospheric distortions. SAR data with high temporal resolution imagery can be used to detect seasonal variations of coastal retreat. The TerraSAR-X (TSX) satellite of the German Space Agency (DLR) is a X-band active microwave system that provides high-spatial (2 m ground resolution) and temporal resolution (11 day repeat period). We used a TSX backscatter time-series from the years 2012, 2013, 2014 and 2015 to analyze rapidly eroding cliff tops along an ice- and organic-rich permafrost riverbank within the central Lena Delta. The images were analyzed using a threshold approach. The clearly visible transition line between undisturbed tundra surface and actively eroding cliff was subsequently mapped for every image. Very high resolution optical satellite images acquired in August 2010 and August 2014 were used to validate the TSX results. In spring 2015 we conducted a GPS survey and installed a time-lapse camera as well as wooden poles with 50cm distance perpendicular to a rapidly eroding cliff top sequence. Time-lapse images were acquired from late June to late August. The TSX extracted annual retreat rates are in the same range as the ones from the optical reference dataset. The intra-seasonal cliff top retreat lines from 2014 showed equal rates of 2 to 3 m per month. The time-lapse field data at the same place showed similar rates in summer 2015. TSX backscatter time-series show a high potential for monitoring rapid permafrost degradation with high spatial and temporal resolution. The results are valuable for the understanding of degradation process dynamics within a summer season. In the second part of the project we will focus on near to surface soil moisture and freeze and thaw dynamics on the watershed scale on Herschel Island, Yukon territory. In summer 2015 we installed four automated stations that measure near to surface soil moisture and temperature within a watershed on Herschel Island.