Abstract
The leading idea of this work is to continuously retrieve glaciers surface velocity through SAR imagery, in particular using the amplitude data from the new ESA satellite sensor Sentinel-1 imagery. These imagery key aspects are the free access policy, the very short revisit time (down to 6 days with the launch of the Sentinel-1B satellite) and the high amplitude resolution (up to 5 m). In order to verify the reliability of the proposed approach, a first experiment has been performed using Sentinel-1 imagery acquired over the Karakoram mountain range (North Pakistan) and Baltoro and other three glaciers have been investigated. During this study, a stack of 11 images acquired in the period from October 2014 to September 2015 has been used in order to investigate the potentialities of the Sentinel-1 SAR sensor to retrieve the glacier surface velocity every month. The aim of this test was to measure the glacier surface velocity between each subsequent pair, in order to produce a time series of the surface velocity fields along the investigated period. The necessary coregistration procedure between the images has been performed and subsequently the glaciers areas have been sampled using a regular grid with a 250 × 250 meters posting. Finally the surface velocity field has been estimated, for each image pair, using a template matching procedure, and an outlier filtering procedure based on the signal to noise ratio values has been applied, in order to exclude from the analysis unreliable points. The achieved velocity values range from 10 to 25 meters/month and they are coherent to those obtained in previous studies carried out on the same glaciers and the results highlight that it is possible to have a continuous update of the glacier surface velocity field through free Sentinel-1 imagery, that could be very useful to investigate the seasonal effects on the glaciers fluid-dynamics.
Highlights
The glaciers are a natural global resource and one of the principal climate change indicator at global and local scale, being influenced by temperature and snow precipitation changes; the glaciers are the largest freshwater reservoirs on the Earth (Heid, 2011)
Among the parameters used for glacier monitoring, the glaciers surface velocity is an important element, since it influences the events connected to glaciers changes (Heid, 2011) (Karpilo, 2009) (Rolstad and Norland, 2009)
An outlier filtering procedure based on the signal to noise ratio (SNR) values has been applied in order to remove from the analysis unreliable points. We applied this method to several glaciers, starting from Baltoro,located in the Karakoram mountain range, Kashmir region (North Pakistan) in order to highlight the advantages and the drawbacks of computing surface velocity using Sentinel-1 data
Summary
The glaciers are a natural global resource and one of the principal climate change indicator at global and local scale, being influenced by temperature and snow precipitation changes; the glaciers are the largest freshwater reservoirs on the Earth (Heid, 2011). The surface glacier velocity can be measured using both in-situ survey and remote sensing geomatic techniques. The in-situ surveys are accurate and have the advantage of allowing ice flow monitoring at a high temporal resolution, it is difficult to cover wide and not accessible areas; GPS surveys could be expensive and does not allow the acquisition of enough points to investigate the complex ice-dynamics (Karpilo, 2009). Both optical and SAR satellite imagery enable the continuous monitoring of wide areas of the Earth surface and provide information independent from logistic constraints
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