indslide
aps are
| would
hed by
ty (77)
ie other
ron 1:
pair of
solution
st be at
r form.
000 is
created
eas, but
s which
by by
graphic
00 are
data
e old
jility of
JEM is
relation
;reating
| area is
te GIS
ated by
station)
or by means of photogrammetry. There are two
possibilities:
a) the terrestrial photogrammetry proves very good for
the description of known landslides; it is also useful
for the time monitoring.
b) the aerial photogrammetry, such as high resolution
remote sensing, can be used for the detection of
unknown landslides or for a very large landslides.
The full automatic process for the creating of the DEM
can be used, however, it is normally applied in the case
of aerial photogrammetry, by calculating orthophotos
(perpendicular parallel projection). In such a case, the
DEM from 1 : 7 000 aerial stereo pair photos is made.
The other possibility is the spatial (3D) measurement
and data capturing on the stereoscopic model created
on the analog or analytic machines or on the digital
photogrammetric workstation. It is better for special
defined areas (the known landslides). The scale of
stereo images must be set on maximum (from a low
flight, for example, the used image scale 1: 7 000).
The using of satellite stereo images depends on the
size of land changes (landslides). Stereo images from
the SPOT (spatial resolution 10 m), IRS (5.8m) or the
scanned Russian satellite photo images with different
spatial resolution (2-15m) are used. Today's satellite
data do not have ideal spatial resolution for the
detection of small landslides and such a procedure is
very costly. In many cases, false - colour films
(infrared-diapositive) for the photo flights and aerial
photo imaging are used. This type of film provides
multi-purpose uses, for example, photo interpretation,
land use or land cover.
4.3 Spatial analysis of DEM
If both the reference and the new DEM are in a raster
form, the analysis is very simple. It is based on the
difference in georeferenced raster images. On this
level, the professional remote sensing software
packages must be used. The most frequent use is
probably the analysis on a GIS basis, where special
functions for the data analysis (such as overlay
function) are applicable. The long time monitoring is,
at present, made only by means of GIS technique.
4.3 The testing area
There are two great landslide hazard areas in the Czech
Republic. A new landslide area has appeared after the
flooding in Moravia in summer 1997. The traditional
landslide area is the Bohemia Brown Coal Basin. There
are also landslides caused by a previous mining
activity. As a testing area, a part of the Bohemia Brown
Coal Basin in the North-West of-the Czech Republic
was prepared. In this area, testing sites were
established for the landslide detection. For the creating
of the new DEM, photogrammetric stereo pairs are
used. In this case, the testing site was used and
photographed with an aproximate scale 1: 6870 from
the flight height of about 1300-1400m using MRB
15/17 camera with focus of 152mm. The
photogrammetric snaps (5902,5903) were taken on 16
of April 1982. The reference DEM was created by the
digitalization of contour lines from the existing
topographic maps (from the year 1980).
4.4 Data processing
Both left and right images were scanned on HP scanner
with geometrical resolution of about 600 DPI (1 pixel
=30cm). Two methods for the processing of stereo
images were used :
- The full automatic process (automatic image
correlation for the DEM and for orthophoto creating);
the EASI/PACE AD software were used (PCI Canada,
software for processing digital images).
- The stereo image processing on the
photogrammetric workstation DVP Leica; in this case,
a grid of a spatial object point was manually created
and processed. Processing was made by SCOP
software (TU Wien, SCOP is a program system to
process and maintain digital data describing the terrain
or other surfaces) for the vector form or by
EASI/PACE for the raster form.
Intemational Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 589
