SYNERGY OF TANDEM-X DEM DIFFERENCING AND INPUT-OUTPUT METHOD FOR GLACIER MONITORING Helmut Rott 1, 2 , Jan Wuite 1 , Dana Floricioiu 3 , Thomas Nagler 1 , Stefan Scheiblauer 1 1 ENVEO IT, Innsbruck, Austria 2 University of Innsbruck, Austria 3 DLR IMF, Oberpfaffenhofen, Germany ABSTRACT The TanDEM-X/TerraSAR-X satellite formation, applying bistatic radar interferometry, delivers precise, spatially detailed topographic data, an excellent basis for mapping glacier volume change. Repeat pass data of these satellites are used for mapping glacier motion, key information for investigating the dynamic response of glaciers to changing boundary conditions. The synergistic analysis of these data sets provides main glacier parameters: the total net mass balance at annual and multi-annual intervals, the surface mass balance providing the link to atmospheric forcing, and ice export due to calving which is sensitive to changes in ice dynamics and ocean properties. The methods and capabilities of the TanDEM-X mission for delivering these parameters are described. The application is demonstrated for outlet glaciers of the Antarctic Peninsula that have been subject to major dynamic instability in recent years after collapse of buttressing ice shelves. Index Terms — Glacier, mass balance, topography, SAR, TanDEM-X 1. INTRODUCTION During recent years the downwasting of ice masses became the main contributor to global sea level rise, exceeding the impact of ocean thermal expansion [1]. Besides, in many regions glaciers are important sources of water, the future availability of which is jeopardized due to glacier retreat. The decline of the ice masses is subject to high temporal and spatial variability. In order to develop realistic scenarios on glacier response to climate change, it is important to accurately monitor the temporal changes of the ice masses and quantify the processes linking glacier mass balance to the driving parameters of the atmosphere and ocean systems. Precise measurements of surface elevation change by satellite sensors are a main data source for deriving the mass balance of glaciers. In order to relate changes in glacier mass balance (GMB) to climate parameters, it is necessary to resolve also the individual components of the mass exchange between glaciers and the atmosphere/ocean environment. The TanDEM-X/TerraSAR-X satellite formation offers excellent capabilities for investigating these issues, delivering spatially detailed data on elevation change and glacier motion as key parameters for GMB studies. 2. SATELLITE-BASED METHODS FOR GLACIER MASS BALANCE The change in volume and mass of calving glaciers and ice streams is governed by two main processes that are temporally and spatially highly variable: (i) the surface mass balance; (ii) the ice export due to calving. The change of ice mass in time of a calving glacier (the total net mass balance B n ) constitutes the sum of the total net accumulation B ac , the total net ablation B ab , and the ice export B cv due to discharge through a gate Y at the calving front: ( ) [ ] cv Y cv ab S n ac S n cv ab ac n B SMB dy H(y) (y)ρ u dS b + dS b = B + B + B = t B - = - = Δ ∫ ∫ ∫ (1) ρ is the density of ice, u cv is the velocity normal to the calving front, H is the ice thickness, and the y-coordinate is aligned parallel to the calving front. S ac and S ab represent the accumulation and ablation area; b n is the specific net mass balance [kg m -2 a -1 ]. The surface mass balance (SMB) is the net gain or loss in mass deposited/depleted on the glacier surface over the time interval Δt. Two remote sensing based methods are applied for retrieving the mass balance of calving glaciers and ice streams: (i) the geodetic method, measuring the change in surface topography and glacier volume; (ii) the input/output method (IOM). For the geodetic method two precise DEMs at different dates are needed to derive the volume change over this time span by means of DEM differencing. For converting volume change into mass change, an estimate on density of the added or depleted volume is needed.