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Full-Value Mapping of Glacier Rheology Using Repeat Pass SAR Interferograms

Aleksey SHAROV(1) and Sven ETZOLD(2)

(1) Joanneum Research, Wastiangasse 6, A-8010 Graz, Austria
(2) Dresden University of Technology, Mommenstraße 13, 01062 Dresden, Germany

Abstract

FULL-VALUE MAPPING OF GLACIER RHEOLOGY USING REPEAT PASS SAR INTERFEROGRAMS

Aleksey I. Sharov (1), Sven Etzold (2)

(1) Institute of Digital Image Processing, Joanneum Research, Wastiangasse 6, 8010 Graz, Austria (2) Institute for Cartography, Dresden University of Technology, Mommenstrasse 13, 01062 Dresden, Germany

The advancement of differential radar interferometry (DINSAR) in the 1990s established unprecedented technical capabilities for detecting and measuring the deformation and flow of glacier ice, and gave a strong impetus to the study of glacier rheology from space. Numerous examples were already shown of successful DINSAR applications to studying three-dimensional flow of large glaciers, measuring short-term glacier velocities and identifying surge effects on ice fields. It has been demonstrated that the DINSAR method is applicable to precise rheological modelling in different glacial environments and that interferometric models of ice-surface rheology can be perfectly represented in the most versatile and easily interpreted form of satellite image maps.

Nevertheless, most research in the area is presently focussed on designing and validating algorithms for DINSAR data processing, while comparatively little attention is paid to appropriate cartographic representation of the glaciological information derived from interferometric surveys. This is quite evident from reviewing the interferometric maps of European glaciers published so far; most of them fall into the category of simple and hasty reproductions or provisional maps at best. Precise and elaborate DINSAR maps representing glacier dynamics in legible metrical form are still very few in number. This is presumably due to the algorithmic complexity of DINSAR and some uncertainties in the performance of this novel and somewhat unaccustomed technique, making the involvement of traditional cartographic skills and expertise difficult.

The present paper reports on the results and experience gained in producing detailed rheological maps through the use of repeat-pass interferometric SAR data obtained from ERS-1/2 satellites over large European glacial areas including Hintereisferner, a typical valley glacier in the Austrian Alps with a long history of surveys, and the Svartisen Ice Caps in Northern Norway, an important site for hydropower production. An original and stringent albeit very simple algorithm has been applied to the reconstruction of glacier rheology from interferometric phase gradients (GINSAR) that does not involve complex process artifices, does not require accurate reference topographic models and provides fast, global and reliable solutions for: - unsupervised detection of glacier motion/changes, - quantitative evaluation of the glacier strain rate and ice velocities, - distinguishing areas with different degrees of ice deformation and places where crevasses might occur, - representation of glacier rheology and morphology in the form of high-resolution image maps. The GINSAR approach mitigated some problems related to the operation of interferometric phase unwrapping, thus improving mapping accuracy. Besides, fewer additional a priori assumptions had to be made on the character of glacier motion and glacier topography.

An experimental data set included all necessary Austrian and Norwegian topographic maps, multitemporal instrumental records documenting the rate of glacier ice flow and 7 pairs of SAR interferograms taken under steady cold weather conditions, which were processed with the RSG 4.6 software package. Cartographic styling, drafting, scribing and editing were performed using the ArcInfo and FreeHand software. Some developments in cartographic design and symbolisation contributed their share to the aesthetic appearance of map sheets. As a result 12 colour image maps including

· an overview map showing the distribution of the glacier strain rate in the Svartisen area at 1:100 000 scale,

· eight detailed maps showing ice velocities and glacier marginal changes at Engabreen, Fingerbreen, Frukostindenbreen and Storglombreen outlet glaciers in the Svartisen test site at 1:50 000 scale,

· two maps of the glacier strain rate and glacier velocities in the Hintereisferner test site at 1:50 000 scale,

· an auxiliary map showing glacier marginal changes in the Hintereisferner test site at 1:25 000 scale

were compiled, printed and verified on a cost-effective basis, thus completing the whole processing chain.

Map quality control and content review was performed in 2002 and 2003 during terrestrial surveys and observations using high-precision geodetic equipment. The average tachometric accuracy of the GINSAR maps was estimated at ± 2.0 cm/day. They proved to be invaluable both in the detailed planning of field campaigns and in the identification of various surface features and critical areas for which ground information was needed. High metric quality and detail, consistent and complementary information contents, proportionally long legends, conformity with available standards, attractive appearance and the wide range of possible applications provide ample proof that our final cartographic products can be regarded as full-value maps.

 

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry