Scott Polar Research InstituteINTEGRAL
Franz-Joseph land
|
The Franz-Josef Land archipelago - the northernmost part of the European arctic terra firma - consists of numerous, mainly dome-like islands covered with multi-year ice. Because of geologically recent volcanic activity many islands have steep rocky shores and basal cover, determining their plateau-like shapes in the center. The glaciers slipping down from the continental parts of the archipelago produce many icebergs, which may be encountered in the surrounding waters. |
|
In the archipelago, glaciers occupy 55 from ca. 190 islands and the glaciated coastline extends for ca. 2520 km (http://dib.joanneum.at/integral). The fronts of active outlet glaciers constitute approx. 59% of the ice coast and contemporary topographic maps and hydrographic charts show more than half of the calving ice coasts by dashed lines, i.e. as uncertain coastlines. Maximum frontal velocities of tidewater glaciers reach 250 to 400 m/year. The total glaciated area exceeds 13,500 km and the mean ice thickness appears to be close to 180 m. The Southern Glacial Complex covering ca. 2,150 km on Prince George Land is regarded as the largest ice mass in the archipelago. There are very few data on ice thickness and ice flow velocities at glacier fronts, and the rate of change in ice flow and thickness is practically unidentified.
The northeastern part of Franz-Josef Land differs from the remaining area by more severe weather conditions, leading to the fact that the straits between islands are covered with pack ice all the year with the possible exception of rare late-summer ice cover breaks on the south of archipelago.
Annual average temperature is very low, the highest temperature in January is 100, and most precipitation occurs in late spring and autumn. Consequently, temporal decorrelation due to precipitation or melt effects is unlikely to be a serious issue for interferometric SAR acquisitions in winter.
|
For Franz-Joseph Land a JERS SAR interferometric pair covering the eastern part of the archipelago in the winter of 1998 was acquired (see right). The selected image pair has an acquisition time interval of 44 days and a short baseline and was acquired during favourable weather conditions. The image swath, running from north to south, covers islands Eva-Liv, La Ronciere, Vilchek, Gall and Salm. |
|
|
|
Left: Flattened and filtered JERS interferogram of January 6 and February 19, 1998. Look direction (descending mode) is indicated by the arrow (incidence angle ~35), the perpendicular baseline is 190 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 Franz-Joseph Land derived from JERS offset-tracking between SAR images of January 6 and February 19, 1998. The relatively long repeat period leads to the fact the displacements of the glaciers are more than 1 pixel. The offsets between the JERS SAR images were therefore computed in slant range and azimuth directions in order to estimate the glacier motion. The result shown in this figure indicates a very attractive outcome, highlighting the fastest moving glaciers. For this JERS image pair of Franz-Joseph Land the azimuth shift modulations are very limited. The very good results over the fastest moving glaciers would suggest that also after 44 days the speckle at L-band is retained. |
|
