Thus, stereophotographic and INSAR data provide additional
and complementary information for analyzing and modeling
glacial topography. Joint application of these image data is
therefore highly expedient for high-quality topographic
monitoring in the High Arctic at different scales. The data can be
combined either by merging the interferogram with
stereographic data, as suggested in Section 3.2, or by aligning
interferometric features to the orthophoto. In both cases some
preprocessing steps are necessary. In this context, the procedure
of high-pass filtering provides a valuable tool for converting the
interferogram into the graphic layer (See Fig. 9, d).
4. CONCLUSIONS ON THE KINDS AND ORIGIN OF
TOPOGRAPHIC CHANGES IN FJL
Several important conclusions can be derived from the results
obtained during the present environmental studies in FJL. They
can be briefly summarized as follows.
1. The extent of changes revealed at glacier termini clearly
shows the strong tendency of relatively rapid glacial retreat in
the FJL archipelago. The continuous advancement of the largest
outlet glaciers might be probably caused by their inertial
movement and does not contradict the common trend of glacial
retreat in FJL. Although the absolute values of glacial changes
detected in FJL are smaller than in the Spitsbergen and Novaya
Zemlya archipelagoes, the relative areal changes of several
percents for the past 40 years are rather significant.
2. The average rates of glacial retreat differ, however, from those
obtained by other investigators. Surveys repeatedly performed in
1957-1959 at glacial borders of Sedov and Churlyonis ice caps
showed the mean annual rate of glacial retreat to be 13-16 m and
5-6 m per year, respectively (Grosswald et al. 1973). The annual
values of glacial retreat, which can be deduced from the results
of present ,,indoor* measurements given in Table 4, don't exceed
2.5 - 3 m/a at the same sites. Moreover, a comparison with
historical maps compiled in 1874, 1880, 1897, 1899, 1900, 1903,
and 1914 leads to the assumption that glacier changes in FJL
occur on a fluctuating basis.
3. Climatic changes (warming, etc.) in the High Arctic are the
most obvious reasons for the present glacier retreat in the FJL. A
general negative balance of the FJL's glaciers has remained
negative since 1930 (Koryakin 1985) and related to climatic
changes. Much less attention is paid to the other geophysical
agents which could influence the present glacial retreat in the
archipelago. In the author's opinion tectonic and seismic reasons
should not be forgotten in investigating the origin of glacier
changes in FJL. Drastic destruction of glacial fronts and active
calving could probably be stimulated by seismic activity in the
area in spite of the fact that the High Arctic seldom experiences
strong earthquakes. The geological map published in 1995 by the
American Geographic Society, for example, shows only two
earthquakes greater than magnitude 6.0 having occured in the
20th century northwards of 81? latitude. However, the epicenters
of both earthquakes were located within a distance of 200 km
from FJL.
4. One more explanation for the rapid destruction of ice shelves
and glacier tongues can be given by analyzing local changes in
the sea level and vertical tectonic movements in the archipelago.
Large alterations in the sea level caused by heavy winds and
rapid subsidence of the glacier bed could also provoke the
disjoining of floating ice shelves from the grounded glacier part
and the removal of icebergs from coastal waters. The occasional
summation of both factors will inevitably result in fast fracturing
of floating glacier tongues. Several significant calvings detected
in FJL as well as the disappearance of Mother-of-Pearl Island
mentioned in (Kostka, Sharov 1996, b) are supposed to be
directly related to the subsidence of the glacier bed.
5. There are many other factors ranging from geophysical to
biological reasons that contribute to the present topographic
effects, but, unfortunately, we have no ready mechanism reliably
explaining the character of all topographic changes in FJL.
Further investigations using differential radar interferometry are
presently being carried out for determining rates of glacial flow
and better understanding of topographic phenomena in this area.
ACKNOWLEDGMENTS
The valuable comments of Dr. O.Hellwich, Technical University
of Munich, and the kind assistance in image procurement and
processing provided by Dr. L.Kenyi, Joanneum Research, Graz,
are gratefully acknowledged.
REFERENCES
Atlas of the Arctic, 1985. GUGK, Moscow, pp. 204.
Barr, S., 1995. Franz Josef Land. Polarhändbok. NPI, Oslo, pp.175. -
Brandstátter, G., 1993. Transformation to the normal case of general
non-calibrated projective stereo pairs. Proc. of the 2d conference on
optical 3-D measurement techniques, Zurich, pp.8
Brandstätter, G., 1997. Introduction. In: The Franz Josef Land
Archipelago - Remote Sensing and Cartography. Justus Perthes
Verlag, Gotha, p.10-11.
Dowdeswell, J. et al., 1994. Evidence for floating ice shelves in
Franz Josef Land, Russian High Arctic. J. Arctic and Alpine
Research, v. 26,No.1, p.86-92.
Diament, A. et al. 1993. Using GIS to study Arctic ice caps. GIS
Europe, v. 2, No. 6, p.22-25
Grosswald, M. et al, 1973. Oledenenie Zemli Frantsa-losifa
(Glaciers of Franz Josef Land). Nauka, Moscow, pp.352 (in Russian)
Hartl, Ph., Thiel, K.-H., 1993. Radar interferometry. Basic concept
and applications. In: International Mapping from Space. Proc. of
ISPRS, v. 15, Hamburg, p.207-232.
Hellwich, O. SAR phase unwrapping: implications of terrain shape
and smoothing. pp.6 (in print).
Kenyi, L. et al., 1996. SAR interferometry: experiences with ERS-
1/2 SLC data. Vermessung & Geoinformation, Heft 2, p.157-163.
Koryakin, V.S., 1988. Ledniki Arktiki (Glaciers of the Arctic).
Nauka, Moscow, pp. 160 (in Russian).
Kostka R., Sharov A. 1996 a). Interpretation of several European
glacial areas in spaceborne photographs and radar imagery. Proc. of
the 15-th EARSeL Symp. Balkema-Rotterdam, p.203-212.
Kostka, R., Sharov A., 1996, b). Operational image-based mapping
in the Franz Josef Land archipelago. IAPRS, v.XXXI, Part B4,
Druckerei Berger, Horn, p.469-475.
Lefauconnier, B. et al., 1993. Validation of SAR data from ERS-1
on Spitsbergen, Svalbard: preliminary glaciological and
geomorphological interpretation. Proc. of the 2-d ERS-1 Symp., v.1,
Hamburg, p.171-176.
Matishov, G., 1993. Environment and Ecosystems of the Franz Josef
Land (Archipelago and Shelf). KSC, Apatity, pp. 264.
Sharov, A., 1997, a). Practical application of satellite
phototopography to mapping tasks in Franz Josef Land. Petermanns
Geographische Mitteilungen, Ergánzungsheft 293, Justus Perthes
Verlag Gotha, p.57-82.
Sharov, A. 1997, b). Development of theory and methods for the
satellite topographic monitoring in the High Arctic. Habilitation,
MIIGAiK, Moscow, pp.306 (in Russian).
Vinogradov, O., Psaryova, T., 1965. Katalog Lednikov SSSR.
Zemlya Frantsa-losifa (Catalogue of Glaciers of the USSR. Franz
Josef Land), v.3, Part, Gidrometeoizdat, Moscow, pp.144( in Russ).
210 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998
