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measured by GPS as 80°50,201'N and 57°29,513'E. We ought
to note that there is a theory about the existence of two small
islands near the southern coast of Ziegler Island, which is based
on the analysis of aerial photographs (Govorukha, Mikhalenko
1964; cited from Grosswald 1973). We saw only one islet there.
The inspection of the present state of 17 geodetic signals
showed that more than half of them do not exist any more,
several have been destroyed or are being destroyed by strong
winds and other agents. Precision spirit leveling was carried out
at Bell, Hall, Hayes, Komsomolskiy and Ziegler islands, and
present elevations h, of 5 geodetic spots and 2 bench marks
were measured with relation to the current sea level.
Subsequently, corrections were introduced, taking into account
the difference V j between the current and multiyear mean
levels of the Barents Sea recorded at the tidal station on Hayes
Island and calculated on the basis of archival data acquired at
the Krenkel station and at the Direction of Hydrometeorological
Service, Dikson (Annual data...). Corrected elevations H i
were compared with elevations H o; Which had been recorded
40 years before, and differences AH ; Were calculated in
accordance with the following expression
AH,-h *V,-H,
j» Where
V, = Po; - Po; =D; +0 = Po
with Do js Do j denoting, respectively, current sea level and
multiyear mean sea level, both related to the tidal datum of the
tidal station; D; is the current reading on a tide staff related to
the staff 's zero point and Ô is a reduction value reducing sea
level to the tidal datum. The results of calculations using
Do; 7 0.88 m are given in the table below.
Table. Recent changes in elevations measured in FJL
i| Station o2 m V, ,m | AH, m Wind
dir., m/s
est. year
1| Ziegler 81.4 - 0.02 - Calm
gs * 1950s
2 Bell 17.9 - 0.07 - 0.06 SW 2
g.s ** 1950s
3 | Hall/Littr 8.6 +0.17 - 0.69 ENE 3
g. s. ** 1950s
4 | Hayes 54.7 +016 | -0.20 NNE 4
gs * 1950s
5 | Komsol. 40.2 - 0.02 -24 EF. 9
gs. * 1950s
6| Hayes 12.0 +0.04 - 0.12 NE 4
bm N2** 1969
7| Hayes 4.8 +0.04 - 0.09 Calm
bm N4** 1977
*)single-run; **)double-run.
Measurements were carried out using a N3 precision instrument
and a 4-meter leveling rod and were characterized by a
maximum section length of 1,200 m and maximum closures of
I9 mm. A single error in writing results prevented the
calculation of A H ; for the geodetic signal on Ziegler Island,
where only a single-run was done by leveling. Steady results of
473
measurements at other stations show the present subsidence of
the islands and indicate the isocatabatic surface to be tilted from
the west to the east, which corresponds to earlier observations.
There might be a relationship between these vertical motions
and the recent destruction of ice shelves in FJL. Unfortunately,
we have no ready mechanism explaining the character of such
vertical movements, but, nevertheless, the present results are of
fundamental significance and served as an important aid in
photogrammetric mapping.
3. PHOTOGRAMMETRIC MAPPING ON PC
Satellite image maps presenting all surface details in their real
appearance with the addition of conventional graphic elements
are ideal for depicting high arctic areas, where natural features
are predominant, complicated socio-economic objects are
scarce, the relief is mostly homogeneous, and vegetation cover
is negligible. They can be produced relatively quickly and at
low cost, if done on a standard PC.
5.1 Digital mono- and stereoplotting
Image mapping of FJL was performed with reasonable accuracy
and within a relatively short period of time at the Department of
Remote Sensing, Image Processing and Cartography, TU Graz,
by means of digital mono- and stereoplotting on the PC-based
photogrammetric microstation. Fragments from spaceborne and
aerial photographs were initially digitized with different spatial
resolutions and were enhanced to a similar extent so as to
provide comparable scales and interpretabilities of input data.
Thus, spaceborne KATE-200 images digitized with a spatial
resolution of 1250 DPI have a ground resolution of 25 m, which
is the same as that of SAR digital imagery. Digitizing of
spaceborne KFA-1000 images with 2500 DPI and aerial
photographs with 300 DPI also provided digital data suitable for
joint analysis. The image set was subjected to further geometric
homogenization by means of image rectification and by
reducing all image fragments to the normal case using "DVR",
"ERDAS", and "PHOTOMOD" softwares.
Several fragments from KATE-200 photographs were combined
in an image mosaic, and photo coordinates were transformed
into the Gauss-Kriiger coordinate system with a reference to the
available topographic maps. Two small fragments from quick
looks of LANDSAT and SPOT imagery were included in the
mosaicking to cover some blank spots. The planimetric
accuracy of this controlled mosaic covering the whole FJL
archipelago is characterized by an rmse value of ' 125 m,
which was checked with ground control data by an independent
expert.
Digital stereoplotting was performed using "DVP" and
"PHOTOMOD" softwares. Several aerial stereopairs and only
one stereomodel from the KFA-1000 photographs were needed
to cover the Hall Island test area, and one stereomodel from
KATE-200 imagery was used for digital terrain modeling of the
central part of FJL (Ziegler Island). Once the stereomodels had
been set in place and oriented, precise three-dimensional
measurements of topographic features were made, followed by
computer-assisted drawings. Contouring in glacial areas
combined with local interpretation of both optical and radar
imagery did not bring about the essential difficulties we had
expected and actually was even more convenient than
contouring in rocky areas affected by shadows. 3 DTMs and
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996
