epicontinental sea of the Pliocene was desalinated and
brackish water sediments were deposited to layers of up
to 4km thickness. After a period of uplifting and
processes of deposition and deflation during the ice age
the region of the lake subsided about 10000 to 15000
BP, the bottom of the lake was deepened and filled with
water. The eastern parts of the depression were drained
and thus transformed to a lowland moor (Lóffler, 1979,
Tollmann, 1985).
Since 1921 the region is divided by the Hungarian-
Austrian border. About 90km? of the lake and its reed
belt belong to the Hungarian, 230km? to the Austrian
territory (Csaplovics, 1984).
increased when traditional
extensive grazing of the puszta (grasslands) was
displaced by single-crop farming. In Austria the
economic potential of wine-growing and tourism was
exaggerated to a great extent during the last decennia.
Though sewage purification plants have been installed
all around the lake over-fertilization of fields and
vineyards as well as waste water spills from camping
sites still deteriorate the water quality of the lake. The
lake itself is overused by crowds of summer tourists.
Uncontrolled harvesting and burning of reed endanger
breeding habitats of rare migratory birds. The Hungarian
border region is lately open to public. Therefore large
areas of the southern parts of the lake and of the
grasslands remained relatively undisturbed.
Recently Austrian and Hungarian authorities established
a national park following the criteria of the International
Union of Conservation of the Nature (IUCN). The
Hungarian-Austrian Fertó Tó National Park consists of
about 72km? of primary zone areas and of about 60km?
of secondary zone areas.
Environmental problems
2.DIGITAL TERRAIN MODELS OF LAKE FERTÓ
Since the early eighties needs for creating, maintaining
and applying a geographical information system of the
lake and its surroundings forced research in various
fields of remote sensing and GIS, like multitemporal high
resolution photo-interpretation and digital image
analysis, multithematic inventory and integration of
environmental data pools into GISs, analysis of high
resolution space photography, and production of digital
orthophotos (Csaplovics, 1982, Csaplovics, 1987,
Csaplovics, 1993).
Soon limnologists, hydrobiologists, ecologists and others
claimed urgent need for high resolution digital terrain
data of the bottom of the lake. Research on structure
and vitality of the reed belt, on dynamics of
sedimentation in off-shore and reed-water-interaction
zones needed digital terrain models containing
informations on the variations of water depths
respectively sediment layer thicknesses. Creating tools
for monitoring and simulating the ecological situation of
the lake and its surroundings was the focus of
interdisciplinary work.
168
From 1985 to 1988 work for the compilation of the
digital terrain model of the Austrian part was carried out.
Based on the methodology of trigonometric height
measurement flexible interaction between master- and
remote stations allowed the coordinate determination of
grid-like arranged points describing the bottom
topography of the lake. Calculation of refraction and
correction of the measurements minimized mean height
errors to lower than +/-2.5cm for a horizontal distance
of 3km. By treating data with the SCOP-DTM-software
(Stuttgart Contourline Program, Kraus 1993) digital
terrain models of the sediment surface and the ground
surface of the bottom of the lake have been calculated.
Contour line maps of both surfaces - limited by the
contour line 116.50m - have been derived. Extensive
silting up in the reed belt could be documented. Profiles,
calculations of sediment volumes and selected
perspective views of the bottom surface are further
results of the analysis of the Austrian DTM data
(Csaplovics, 1989).
in 1990 a joint research program supported by the
Austrian Ministry of Research and the Hungarian
Academy of Sciences raised the opportunity to complete
the digital data pools by integrating the Hungarian part
of the lake. Austrian and Hungarian scientists adapted
the methodology of data collection and data treatment
to the Hungarian situation (Csaplovics et al., 1993).
Problems of coordinate transformation caused by
different reference ellipsoids and different sea level
reference points had to be solved (Bácsatyai, 1995).
Parallel to field missions in Hungary the existing DTM
files of the Austrian terrain models had to be prepared
for integration of the Hungarian data. In 1995 the final
digital terrain models of Lake Fertó have been created.
These models consist of data sets of both the sediment
surface and the ground surface of more than 350km? of
the bottom of the lake, the reed belt and the terrain of
surrounding areas limited by the contour line 116.50m.
More than 10000 points per terrain model have been
calculated by using the facilities of the SCOP-software
As the terrain is very flat, contour line intervals of 10cm
meet the requirements of limnologists. On the other
hand methodological, technological and organizational
constraints had to be overwhelmed to reach these
accuracies in praxi. Profiles, perspectives of selected
sceneries, thematic maps showing variations of dry
areas in function of simulated seasonal and/or annual
variations of water levels are further thematic
components of the DTM-package (figure 1).
Combination of these data with thematic overlays, e.g.
maps of breeding places of protected rare birds, enlarge
the efficiency of interdisciplinary applications of the
DTMs to a great extent. Diagrams of areas and volumes
of the water body of the lake in function of varying
water levels meet the needs of hydrologists for exact
modelling of the lake. Intersection of the digital terrain
data of sediment and ground surfaces allows the
computation of a difference model and the calculation of
volumina respectively isolines of thickness of sediment
layers (figure 2).
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B7. Vienna 1996
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