Rock Glacier Activity in the South Shetland Islands: DINSAR, Ground-truth and GIS Analysis. Methodology and First Results

Paper accepted for presentation at the 2010 European Space Agency Living Planet Symposium, Bergen, Norway, 28 June to 2 July 2010:

Jorge, Marco; Vieira, Gonçalo; Catalão, João; Ramos, Miguel

“Rock glaciers are distinct lobate or tongue-shaped bodies of permafrost that flow in response to the deformation of the ice within. Rock glaciers are relatively rare in oceanic environments so that their study is particularly important and relevant in maritime Antarctic (Serrano & Lopez-Martinez, 2000). Furthermore, being located in a region where the climate warming is particularly strong, the South Shetlands archipelago is a privileged place for investigation on the response of permafrost degradation and deformation rates to the climatic forcing. The ice-free coastal zones where the rock glaciers occur show mean annual air temperatures slightly below 0°C, making this region one of the best places on Earth to study the response of rock glaciers to climate change.

“In the South Shetlands, the field work logistics are complex, mainly due to the limitations on transport, harsh weather conditions, but also accouting for the environmental impact restrictions imposed by the Antarctic Treaty. Therefore, the use of active remote sensing systems is an excellent way to monitor the deformation of the terrain where rock glaciers occur. Serrano & Lopez-Martinez (2000) have surveyed most of the rock glaciers in the archipelago, but data on movement rates is still lacking. Differential interferometry of SAR images (DINSAR) from ERS 1-2 and ENVISAT sensors allow to monitor the activity of rock glaciers parsimoniously (good spatial resolution and measurement accuracy in a large area), in a way that no other technique would permit.

“Our approach focuses on different timescales of activity reflecting distinct climatic controls. “Permanent Scatterers pixels” identified in long temporal series of interferometric SAR images will be used to obtain the inter-annual movement rates of the rock glaciers. Interferograms with temporal baselines from 1 day (tandem pairs) to 1 year will allow to explore the DINSAR signal of each rock glacier. Following the methodology proposed by Lambiel et al. (2009), a classification of all features according to the rate of activity will be made. The specific physical conditions of the study area, the small dimensions of the features being monitored and large differences in rates of activity (i.e., the very distinct DINSAR signals) demand a preliminary focus on the specificity of the DINSAR analysis, a task whose results we will present in the 2010 ESA conference. Field test sites will be installed in Livingston and King George islands in order to obtain ground truth for validation and complement DINSAR results. Hurd rock glacier, in Livingston Island will be the main target of one-year interval detailed geodetic ground surveys using DGPS and Total Laser Station measurements.

“The high rates of geomorphic dynamics of the periglacial terrain provides an opportunity to perform an innovative spatial analysis using the DINSAR deformation grid. Ground deformation data will be analysed using empiro-statistical techniques accouting for different independent variables (e.g., bivariate analysis – informative value and GLM – logistic regression), such as: i) detailed geomorphological surveys; ii) geographical variables derived from the DEM; iii) and field data from monitoring sites maintained by our group, such as weather stations, shallow and deep boreholes for permafrost monitoring, active layer thickness (CALM sites) and snow mantle thickness. The deformation grid is a clear dependent variable, with no problems of multicollinearity with the variables assumed and inputted in the models as explanatory-independent variables, that can be used in two distinct but related levels of analysis: i) the relationship between the classified geomorphic features (geomorphological mapping) and the movement of the terrain; ii) the influence of the geographical factors on the terrain deformation. By combining i and ii we should reach a better level of knowledge on periglacial dynamics.”