Volume changes 2000 - 2011/2012 and dynamics on the Patagonia Icefields from TanDEM-X and TerraSAR-X Data
Floricioiu, Dana¹; Abdel Jaber, Wael¹; Rott, Helmut^2
1German Aerospace Center (DLR), GERMANY; ²University of Innsbruck & ENVEO IT, AUSTRIA

The behavior of the Patagonia Icefields, the largest temperate ice masses in the Southern Hemisphere, has been subject of several studies due to its importance for understanding the global climate system. Recent global low resolution mass estimates for glaciers and ice caps show significant mass deficit for many ice covered regions over the world including the Northern and Southern Patagonia Icefields (NPI and SPI). We are taking advantage of the currently increasing availability of global elevation data acquired from Synthetic Aperture Radar (SAR) systems to provide a more detailed analysis over these areas.

The ongoing TanDEM-X satellite mission was launched in 2010 and is dedicated to the data acquisition and generation of a high resolution interferometric global Digital Elevation Model (DEM) which will be available after the end of the mission. Currently, only TanDEM-X experimental data have been made accessible to the science community as Co-registered Single-look Slant range Complex (CoSSC) format. These products enable the users to process own DEMs for specific areas. An objective similar to TanDEM-X was reached one decade earlier by the Shuttle Radar Topography Mission (SRTM) of 2000 which provided the most complete and accurate DEM at the time covering the entire land areas from 56°S to 60°N.

We are using SRTM and the TanDEM-X multitemporal elevation dataset to accurately compute ice elevation, volume and consequently mass changes of SPI and NPI in the period 2000 - 2011/2012. In order to achieve a better calibration between different DEMs and to analyze intermediate temporal trends of topography we included in our study several ICESat Geoscience Laser Altimeter System (GLAS) surface height tracks available from 2003 until 2009. Distinct trends in surface elevation change over the last decade are exhibited by this comparison. The surface lowering of major Patagonia glaciers in the period 2000 - 2011/12 ranges from several tens of meters to values above 100 m at some termini. Exceptions are Perito Moreno glacier with constant elevation in the accumulation and ablation areas and the tidewater glacier Pio XI showing slight thickening.

In order to obtain a comprehensive picture of the ice dynamics we focus also on ice velocities derived from TerraSAR-X high resolution data. Velocity data are required to estimate the ice export due to calving, an important component of the mass balance of Patagonia glaciers. We are observing main outlet glaciers which are known to be subject to short term variations in velocity, area and thickness. The complex ice motion and deformation patterns were derived by means of amplitude correlation applied to 11 days repeat pass TerraSAR-X data. The frequent imaging allowed monitoring of large calving events accompanied by acceleration and area loss. Thus drastic decreases in elevation measured from DEM differences may be explained by dynamic thinning affecting some parts of the icefields, for instance the Upsala glacier. For Perito Moreno glacier the TerraSAR-X time series compared to previous velocities based on SIR-C data from 1994 and field measurements confirms the long term stability of the ice flow and is consistent with the unchanged elevation resulted from the DEM difference. The contrasting behavior of different glaciers with respect to ice velocity, ice elevation and front position emphasizes the importance of spatially detailed repeated observations, as delivered by TerraSAR-X and TanDEM-X, in order to understand the complexity of glacier response to climate change.