Semi-controlled interferometric mosaic of the largest european glacier

Publikation aus Digital

Sharov Aleksey I., Dimitry B. Nikolskiy

ESA ENVISAT Symposium in Montreux, Switzerland, April 2006 , 2006


North Island (48,100 km2, 1952) in the Novaya Zemlya archipelago is
 the second largest island (after Iceland) in the Eurasian Arctic,
 and the Main Ice Sheet occupying 47.5 % of its surface is reputed
 to be the largest mass of glacier ice in the "Old World". The last
 extensive aerial and geodetic surveys in Novaya Zemlya were carried
 out in 1952 and available topographic maps of the North Island are
 obsolete and unreliable. There are very few instrumental records
 documenting the rate of glacier ice flow in Novaya Zemlya, and present
 mass-balance estimates for the Main Ice Sheet are very approximate.
 This paper presents the main outcomes of the INTEGRAL (EC FP 6) and
 SIGMA (ESA AO No. 2611) research projects related to the enhanced
 geocoding, interpreting and mosaicking of spaceborne ERS-1/2 and
 JERS-1 SAR interferograms of north Novaya Zemlya. A 50 m posting
 DEM of the study region was generated from available 1:200 000 topographic
 maps and upgraded using the ICESat-GLAS altimetry data obtained in
 2003 – 2005. Six ERS-1/2 and one JERS-1 SAR overlapping interferometric
 models, all obtained from different descending orbits, were orthorectified
 and assembled into a semi-controlled seamless mosaic. Interferometric
 phase distortions at specific target points characterized by the
 locally highest coherence values were reliably estimated, and actual
 topographic heights of main ice divides and ice coasts were precisely
 measured and controlled from the ICESat transects and the phase information
 in between. Significant height errors ranging from -225 m to +313
 m were detected in old 1:200 000 topographic maps at specific locations
 on the glacier surface and corrected in the mosaic. The resultant
 mosaic covers a land area of approx. 18,000 km² (45,000 km² in total)
 and contains 8 information layers: intensity orthoimage, coherence
 orthoimage, fringe orthoimage, phase-gradient orthoimage, composite
 orthoimage, 2-pass differential interferogram (DEM 1952), upgraded
 differential interferogram, and cross-differential ERS-JERS interferogram.
 These layers provided the basis for the interferometric map series
 showing structural morphology, ice-flow pattern and mass-balance
 characteristics of the Main Ice Sheet at 1:500 000 scale in the UTM
 projection, Zone 41N, WGS84. The map series is presented in the form
 of a 5-min animation. 
 Practical mapping work revealed essential changes in glacier elevations
 and termini positions. It was determined that the main ice sheet
 lost at least 200 of ice in the period between 1952 and 2003,
 i.e. nearly 4 The comparison with previous estimates made
 by other researchers showed that land-ice-loss processes in north
 Novaya Zemlya have accelerated by approx. 10 %. Frontal velocities
 of tidewater outlets and corresponding values of the ice flux at
 seaward glacier margins were estimated by analyzing the horizontal
 shift of the coastal sea ice forced by glacial flow. Quantitative
 integral estimations of ice flux were provided for 5 glacial provinces
 of the Main Ice Sheet. Spatial asymmetry in present glacier regime
 was deduced and explained. 
 The analysis of the cross-differential interferogram provided no evidence
 for the geometric impact of radar penetration into dry snow on the
 ice sheet. Our interferometric determinations were validated during
 the field campaigns undertaken in September 2001 and 2003. It was
 concluded that the combination of satellite interferometry and altimetry
 offers a particularly potent solution for the topographic modeling
 of large glacier complexes in the case of insufficient ground control.