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Surface elevation changes of an ice sheet are directly linked to the atmospheric forcing and hence climate changes.
The SEC prototype processing system consists of two different algorithms, crossover and repeat-track, which are merged in order to benefit from the accuracy of the former and the spatial resolution of the latter.
Radar altimeter data from Envisat are used to form the dH/dt estimates. The observation period is 2002–2012. When the processor is ready, ERS-1 and ERS-2 data will be added along with CryoSat-2 and Sentinel-3 data when available. In total, this will expand the observation period from 1991 to the present.
For the cross-over results three-month time periods were used to form time series with a one month time step. For the repeat-track results a least squares approach is used to generate the dH/dt values Using the geostatistical spatial interpolation technique kriging/collocation, the cross-over and repeat-track results are gridded together. The preliminary results, obtained for the Jakobshavn Isbræ drainage basin, reveals a surface lowering near the glacier outlet and near zero values at higher locations.
The IV parameter is used for calculating calving fluxes and detecting glacier changes. The product will be based on a combination of several SAR techniques.
The IV sample product image shows the horizontal velocity magnitude and direction of the Petermann Glacier in North Greenland during the winter 1995/96 derived by applying feature tracking to ERS-2 35 day repeat data and assuming surface parallel flow. The associated error standard deviation is also provided.
The IV measured with space-borne SAR and optical sensors represents the mean velocity within a temporal span ranging from the satellite repeat-cycle (between 1 and 46 days for past and current sensors) to several months (when measurement sensitivity must be improved or when multiple velocity measurements are combined in order to increase the measurement accuracy).
Areas as large as the whole Greenland Ice Sheet are covered by a mosaic of smaller velocity maps representing different time intervals. In the mapping geometry, IV is naturally measured on a uniform grid, which can be resampled to any map-projection given the orbital information and an external digital elevation model.
The Calving Front Location of outlet glaciers from ice sheets is a basic parameter. It is used in ice dynamic modelling for computing the mass depletion due to frontal retreat, and for mapping glacier area change.
This dataset shows the terminus position of Jakobshavn Glacier between 2003 and 2010 in the summer and winter season. The calving front locations are obtained from a selection of ENVISAT ASAR images.
The positional accuracy is limited by the pixel size of the map (90 m). The trend in CFL is clearly visible and indicates a general retreat, except for a slight advance in summer 2006. In 2004 the two main trunks of the glacier got separated, a condition that remains until today. The figures also illustrates seasonal variations: in winter the terminus generally extends further downstream than in summer.
The grounding line separates the floating part of a glacier from the grounded part. Processes at the grounding lines of floating marine termini of glaciers and ice streams are important for understanding the response of the ice masses to changing boundary conditions and for establishing realistic scenarios for the response to climate change. The grounding line location product is derived from InSAR data by mapping the tidal flexure and is generated for a selection of the few glaciers in Greenland, which have a floating tongue. In general, the true location of the grounding line is unknown, and therefore validation is difficult for this product.
Remote sensing observations do not provide direct measurement on the transition from floating to grounding ice (the grounding line). The satellite data deliver observations on ice surface features (e.g. tidal deformation by InSAR, spatial changes in texture and shading in optical images) that are indirect indicators for estimating the position of the grounding line. Due to the plasticity of ice these indicators spread out over a zone upstream and downstream of the grounding line, i.e. the tidal flexure zone. This is also called the grounding zone.
Currently, manual or semi-automated techniques are applied to map GLL on case-by-case basis. The GLL is derived either from observations of surface deformation, applying differential interferometric SAR, by means of repeat altimetry measurements, or from texture and shape in visible satellite images.