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NOVAYA ZEMLYA

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NOVAYA ZEMLYA

The archipelago of Novaya Zemlya lies in the north of Russia. It consists of two major islands separated by a narrow strait. Novaya Zemlya defines the boundary between the Barents Sea and the Kara Sea, and is separated from the mainland by the Kara Strait. The archipelago is lying in the path of numerous cyclones moving from the North Atlantic in the direction of the Novosibirskie islands, along the low-pressure depression. These bring a relatively large amount of precipitation, which may be an important factor in temporal decorrelation of SAR signals. The area is mountainous (reaching a height of 1 km), since geologically Novaya Zemlya together with Vaigach island presents a northern continuation of the Ural Mountains. The northern island contains many glaciers, while the southern one has a tundra climate.

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There are very few instrumental records documenting the rate of glacier ice flow in Novaya Zemlya (http://dib.joanneum.at/integral). During the 2nd International Polar Year in 1932-33, M.M. Ermolaev tried to evaluate the velocity of Shokal'skogo Tidewater Glacier by analyzing the lateral displacement and deformation of coastal sea ice pushed away from the shore due to the glacier flow. Afterward, the velocity of Shokal'skogo was repeatedly surveyed in 1957-1958 and 1969. Measurements showed the steady increase of glacier velocity downstream from 9 m/a near the ice divide to 120 m/a at a distance of 2 km from the glacier front. The maximum velocity value at the glacier front is supposed to be about 150 m/a. The velocity of glacial flow increases notably in warm periods with the most intensive precipitation from July to September, and the summer motion rate is about 2.2 times greater than that in the coldest month.

For Novaya Zemlya a JERS SAR interferometric pair covering the eastern part of the island in the winter of 1998 was acquired.

The selected image pair has an acquisition time interval of 44 days and a short baseline and was acquired during favourable weather conditions. The total area of glaciers imaged by JERS-1 in the northern part of Novaya Zemlya is about 18000 km2. The length of the glacial shield along the ice divide is 344 km, the highest point (above 1000 m) is located in the southern part of the cover. To the north the altitudes are decreasing till 500 m. Almost all the glaciers starting in the area of cover glaciation reach the coast. Usually the outlet glaciers flow is orthogonal to the shoreline.

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Left: Flattened and filtered JERS interferogram of January 28 and March 13, 1998. Look direction (descending mode) is indicated by the arrow (incidence angle ~35), the perpendicular baseline is 390 m. The interferogram was computed with 6 azimuth and 2 range looks with common-band filtering and baseline estimated from the fringe rate.

A very good coherence over the slow moving glaciers can be observed. Decorrelation mainly occurs over the areas with high displacement gradients, in particular along outlet glacier margins with excessive strain rates. On the other hand, the effects on the interferometric coherence of snow and ice melting, snow accumulation or wind drift, and volume decorrelation because of microwave penetration in the dry snow cover and ice are limited.

Right: Velocity map for Novaya Zemlya derived from JERS offset-tracking between SAR images of January 28 and March 13, 1998.

The relatively fast movements of glaciers on the north of Novaya Zemlya leads to the necessity of using offset tracking for estimation of their speed. The offsets between the JERS SAR images were estimated in slant range and azimuth directions in order to estimate the glacier motion. The result shown here indicates a very attractive outcome, highlighting the fastest moving glaciers. For this JERS image pair of Novaya Zemlya the azimuth shift modulations are very limited.

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