Identification Of Active Cryoforms In The Central Andes Of Argentina Using SAR Data

EUILLADES, L. D.; BERNARDI, G.; SOSA, GUSTAVO JAVIER; EUILLADES, P.; CAPONE, AUGUSTO; MIERAS, FRANCO; FONTANA, PEDRO; CARELLI, MARÍA FERNANDA; VALDEZ, DAVID

Helsinki

Workshop; Fringe 2017 Workshop; 2017

Agencia Espacial Europea

In the cryosphere of the Central section of the Andes Cordillera, rock and covered glaciers [1] are both inland freshwater resources and good indicators of regional climate variability [2][4]. Those landforms, tongue or lobed shaped, are developed near at high mountain slopes within permafrost areas [5]. They represent dynamic systems with varying activity, where rock fragments are mixed with ice in different proportions, consisting in a permanently frozen mixed ice-debris core and a top layer suffering seasonal thawing process ("active layer") [6][8]. In this type of systems, the variation in its topography would be motivated by both the seasonal loss and recovery of ice content,and the slope-down gravitational action. Verticals and lateral movements of the detrital surfaces indicate the evolution of the underlying or intrinsic ice mass [9]. In practice, the identification and analysis of some characteristics of these cryoforms can be performed using remote sensing data, being a good complement for the glaciological and/or geomorphological field work. In this work, we present the progress carried out studying a set of rock glaciers located in the San Juan Province, within the Central Andes of Argentina. The main objective of this work is to identify and characterize the cryoforms present in the area in order to obtain a more comprehensive idea of the dynamics of this type of glaciers and their impact in the Central Andean environment. Differential SAR Interferometry (DInSAR) is an extensively and suitable tool to provide ground deformation measurements [10]. However, success in high deformation rate areas, like those involving glaciers, depends strongly on the instrument acquisition policy. Missions with short revisit time become mandatory in order to assess the occurred displacements. When large displacements are expected, an alternative is to employ a SAR amplitude signal based technique (i.e. Pixel Offset PO) [12], [13]. The main drawback of PO is related to its accuracy, what is one order of magnitude worst at least than for DInSAR. Availability of high-resolution SAR systems is an improvement, bringing the precision of the obtained results near to that attainable with DInSAR [14]. Availability of the new ESA SAR mission, Sentinel-1, characterized by a 6-days revisit time, opens a new perspective for studying this kind of environments. The default operation mode, TOPS, that is able to acquire a wide swath of ~250km with interferometric capabilities renders the system an invaluable tool for monitoring wide areas. However, it is important to analyze the capabilities of the system for retrieving the displacements occurred in rock and covered glaciers characterized by a deformation rate between 0.5 to 1 m/y [11], taking into account the spatial resolution of the system. We analyze an area of interest comprises between (S32.25°;W70.58°) and (S31.76°;W69.97) which includes more than 20 rock and covered glaciers. Methodology has been organized as follow. We analyze a set of differential interferograms computed from 4 COSMO-Skymed HImage SAR ascending and descending datasets (39 acquisitions).Then, a set of Sentinel-1 A/B IW acquisitions have been processed in order to compute a set of differential interferograms. Analysis of the retrieved displacement has been performed in order to classify the rock glaciers according to its current state. This work allowed us to make a first performance evaluation of Sentinel-1 SAR data in glacier environments that present slow to medium deformation rates and compare the obtained results against those computed using a high resolution SAR system.