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The Northern and Southern Patagonian icefields (NPI and SPI) have been subject to accelerated retreat during the last decades with considerable variability in magnitude and timing among individual glaciers. We derive spatially detailed maps of surface elevation change (SEC) of NPI and SPI from bistatic SAR interferometry data of SRTM and TanDEM-X f...
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... main payload was a bistatic C-band (5.36 GHz) SAR capable of a 225 km swath achieved applying the ScanSAR technique to four sub-swaths featuring different polarization (HH, VV, VV, HH) and look angles between 30° to 56°. The large number of interwoven acquisitions at higher latitudes contributed 5 to both absolute and relative accuracy as well as to reducing voids: the 9 ascending and 9 descending datatakes covering the Patagonian icefields (Seal and Rogez, 2000) are listed in Table S3. The performance of SRTM was assessed among others by Rodriguez et al. (2005); Brown et al. (2005); Carabajal and Harding (2006); Wendleder et al. (2016). ...
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... furthermore retrieved the SRTM radar brightness images (SRTMIMGR) (NASA JPL, 2014) for the sub-swaths covering the icefields (Table S3) with the purpose of assessing the melting state of the glacier surface. We also used the SRTM Water Body Data (SWBD) (Farr et al., 2007) for statistical and visualization purposes. ...
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... temporal variations of LWC due to changing meteorological conditions cannot be excluded during the nine days of acquisition. On the other hand variations due to the diurnal temperature cycle are unlikely given the time of the Shuttle overpasses (Table S3). ...
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... SECR maps of NPI and SPI after seasonal correction are shown in Fig. 1 Table 1 the SECR, the volume change rate (VCR), the mass balance and the contribution to sea level rise are specified for the entire icefields. Table 2 provides SECR and VCR for NPI glaciers larger than 2 km 2 , Table 3 for SPI glaciers larger than 35 km 2 ...
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Differential SAR Interferometry (DInSAR) is the process of differencing two Interferograms for measuring surface movement with an accuracy of millimeter range. The DInSAR process can be applied to observe glacier movement, earthquake deformations, volcanic activities and rate of subsidence or uplift caused due to the extraction of groundwater or co...
Citations
... Therefore, the estimation and compensation of the penetration bias becomes essential. Different approaches have been followed to address the bias by using indicators of constant penetration bias [7], selected acquisitions during melting periods in order to minimize penetration [8], or empirically derived bias estimates [6], [9]. However, the spatial and temporal differences in penetration, as well as the dependence of the bias on the interferometric baseline hamper these approaches. ...
Synthetic Aperture Radar Interferometry (InSAR) is able to provide important information for the characterization of the surface topography of glaciers and ice sheets. However, due to the inherent penetration of microwaves into dry snow, firn, and ice, InSAR elevation models are affected by a penetration bias. The fact that this bias depends on the snow and ice conditions as well as on the interferometric acquisition parameters complicates its assessment and makes it also relevant for measuring topographic changes. Recent studies indicated the potential for model based compensation of this penetration bias. This paper follows this approach and investigates the performance of two subsurface volume models for this task. Single-channel and polarimetric approaches are discussed for random and oriented volume scenarios. The model performance is assessed on two test sites in the percolation zone of the Greenland ice sheet using fully polarimetric airborne X-, C-, L, and P-band InSAR data. The results indicate that simple models are able to partially compensate the penetration bias and provide more accurate topographic information than the interferometric phase center measurements alone.
... Abdel Jaber et al., 2018;Jaber et al., 2016;Braun et al., 2019;Malz et al., 2018).Jaber et al. (2016) andAbdel Jaber et al. (2018) estimate NPI mass losses of -1.02 ± 0.04 m w.e. yr −1 for 2000-2012 and -0.91 ± 0.04 m w.e. ...
... Abdel Jaber et al., 2018;Jaber et al., 2016;Braun et al., 2019;Malz et al., 2018).Jaber et al. (2016) andAbdel Jaber et al. (2018) estimate NPI mass losses of -1.02 ± 0.04 m w.e. yr −1 for 2000-2012 and -0.91 ± 0.04 m w.e. ...
Andean glaciers are amongst the fastest shrinking and the largest contributors to sea level rise in the world. They also represent crucial water resources in the vast semi-arid portions of this large Andes Cordillera (10°N-56°S), sustaining river runoff during dry periods and buffering the effects of droughts. Despite the widespread shrinkage of these glaciers, direct measurement of glacier fluctuations in the Andes are sparse, short-termed and in many cases incomplete, preventing the accurate quantification of recent ice loss for the entire mountain range. Comprehensively quantifying the magnitude of this loss at different special scales is crucial to better constrain future economical, ecological and social impacts. First, we evaluated the performance of a methodology to calculate glacier mass changes on Andean glaciers using time series of digital elevation models (DEMs) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) stereo images. Over our validation zone, the Northern Patagonian Icefield, we found strongly negative icefield-wide mass balance rates of -1.06 ± 0.14 m w.e. yr-1 for the period 2000-2012, in good agreement with estimates from earlier studies and with a second independent estimate (-1.02 ± 0.21 m w.e. yr-1) obtained by differencing the better resolved Shuttle Radar Topography Mission (SRTM) DEM with a Satellite pour l'Observation de la Terre 5 (SPOT5) DEM. Importantly, this work permitted us to (i) validate "ASTER monitoring Ice towards eXtinction" (ASTERIX) method over the Andes; (ii) confirm the lack of penetration of the C-band SRTM radar signal into the NPI snow and firn except for a small high altitude region (above 2900 m a.s.l.) with negligible effects on NPI-wide mass balance; and (iii) provide the basis for an analysis of NPI mass balance changes during different sub-periods between 1975 and 2016 using additional DEMs. Then, we processed more than 30000 ASTER DEMs to calculate the integrated volume of ice lost by Andean glaciers during the past two decades. Andes-wide mass loss amounts to -22.9 ± 5.9 Gt yr-1 (-0.72 ± 0.22 m w.e. yr-1) for the entire period (or -26.0 ± 6.0 Gt yr-1 including subaqueous losses). All regions show consistent glacier wastage, with the most negative mass balance rates in the Patagonian Andes (-0.78 ± 0.25 m w.e. yr-1) and Tropical Andes (-0.42 ± 0.24 m w.e. yr-1). Relatively moderate loss (-0.28 ± 0.18 m w.e. yr-1) is measured in the intermediate regions of the Dry Andes. The inter-decadal patterns of glacier mass loss is an important contribution of this work, observed for the first time at an Andes-wide scale. We observe steady thinning rates in the Tropics and south of 45°S. Conversely, glaciers from the Dry Andes were stable during the 2000s, shifting to drastic thinning rates during the 2010s, coinciding with conditions of sustained drought since 2010. The evaluation of the imbalanced glacier contribution to river discharge during these two decades revealed that glaciers partially helped to mitigate the negative impacts of this sustained drought in the Dry Andes. The results obtained in this thesis contribute to the understanding of recent Andean glacier evolution at a local, regional and Andes-wide scale. We provide a high-quality, multi-decadal dataset that will be useful to constrain the diversity of present 21st century Andes-wide mass loss estimates, in the pursuit of the good calibration of glaciological and hydrological models intended to project future glacier changes and to improve water resource management in the Andes.
