Exploring the applicability of high temporal resolution SAR for monitoring permafrost landscapes

• Main Authors: Stettner, Samuel, Lantuit, Hugues, Bartsch, Annett, Heim, Birgit, Grosse, Guido, Roth, Achim, Widhalm, Barbara, Antonova, Sofia, Zwieback, Simon
• Format: Conference Object
• Language: unknown
• Published: 2016
• Subjects: Canada; Herschel Island; Yukon; Herschel; Ice; lena delta; permafrost; polar night; Tundra; Siberia
• Online Access: https://epic.awi.de/id/eprint/41194/; https://epic.awi.de/id/eprint/41194/1/2016-05_ESA-LPS_poster_Stettner.pdf; https://hdl.handle.net/10013/epic.48136; https://hdl.handle.net/10013/epic.48136.d001

Permafrost is stated as an essential climate variable by the World Meteorological Organization and is an important physical landscape component of high-latitude environments. The variability of the permafrost ecosystem parameters soil moisture (SM) as well as freeze-thaw (FT) has a strong impact on rapid permafrost degradation, on surface energy and water fluxes as well as on biogeochemical processes. Thus information about the mentioned parameters in high temporal and spatial resolution is important for the understanding of processes in permafrost landscapes. Synthetic aperture radar (SAR) operates independently of cloud coverage and polar night and today’s SAR satellite systems provide imagery with high temporal and spatial resolution. Existing operational satellite SAR data products of SM and FT are available only in coarse-scale resolution. We are investigating high-spatial resolution SAR of TerraSAR-X (TSX), and in future ALOS-2, Sentinel-1, as well as optical very high resolution satellite imagery in combination with in-situ experimental monitoring data to investigate the spatiotemporal variability of permafrost disturbances, SM and FT on the watershed scale. Our study site for rapid permafrost degradation is an actively eroding ice- and organic-rich permafrost riverbank from the so called Ice-Complex within the central Lena Delta, Siberia. Our studies on SM and FT focus on a small scale watershed on Herschel Island along the western Yukon Coast, Canada and can potentially be transferred to the Ice-Complex permafrost landscape in the Lena Delta. Automated micro-stations with near to surface soil moisture and temperature sensors were installed in the Lena Delta (since 2013) and on Herschel Island (since 2015). Field work on Herschel Island and the Lena Delta included handheld soil moisture measurements as well as extensive soil sampling. In spring 2015 we conducted a GPS survey in the Lena Delta along the test site 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. We used TSX backscatter time-series from the years 2012, 2013, 2014 and 2015 to analyze rapidly eroding cliff tops along the riverbank within the central Lena Delta. Pre-processing was performed using the Next ESA SAR toolbox (NEST) and included radiometric calibration and conversion to backscatter coefficient sigma nought, multilooking and an ellipsoid corrected geocoding. We then used a threshold approach to visualize the transition line between undisturbed tundra surface and actively eroding cliff prior to mapping. Very high resolution orthorectified optical satellite images acquired in August 2010 and August 2014 were used as validation datasets for the TSX-derived results. The TSX extracted annual retreat rates are in the same range as the ones from the optical reference dataset. The intra-annual TSX-derived cliff top retreat lines from 2014 at the test site showed rates of 2 to 3 m per month. The time-lapse field data at the same place showed similar results in summer 2015. The TSX backscatter time-series show a high potential for the monitoring of rapid permafrost degradation with high spatial and temporal resolution. The results are valuable for the understanding of intra-seasonal permafrost degradation dynamics. Future work on Herschel Island and the Lena Delta will focus on soil moisture and freeze/thaw dynamics on the watershed scale. ALOS-2, Sentinel-1 and TSX datasets are planned to be used and cross-validated with the field datasets. The presented project is embedded in the German Helmholtz Alliance Earth System Dynamics (EDA) network and builds on existing datasets from the FP7 within the PAGE21 project. TSX-datasets were kindly provided by the Department Land Surface from the German Aerospace Agency (DLR).