SPOT multispectral data and digital terrain model for the analysis of ice-snow fields on arctic glaciers

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Abstract
Satellite data from the Arctic present extensive shaded zones arising from the combination of low Sun elevation and mountainous topography. Field radiometry measurements from training zones on two glaciers in Arctic north-west Svalbard discriminate the different surface states of the glaciers. The SPOT reflectance values have been corrected using the slope orientation and dip parameters from the digital terrain model combined with the corresponding Sun elevation and azimuth. The reflectances of the shaded and illuminated zones have been restored to a new image based on the XS3 versus XS1 bimensional histogram. The pixel values of the new image can distinguish between firn and superimposed ice surface states on the glaciers defined and controlled by field measurements. From the new image a map of the different surface states of the glacier can be produced which is homogeneous in both the shaded and illuminated zones. The boundary between the firn and the superimposed ice can be located on the median and longitudinal profile of the glacier by combining the new image and the digital terrain model. With this method it is possible to locate the boundary between the firn and the superimposed ice and, consequently, the equilibrium line to within 40 m of altitude.