First of all, the distribution and quality of elevation points were
assessed after their extraction. ISAE provides a graphical expression of
the quality status of extracted points (Fig. 3). As expected, areas with
reduced quality and/or limited distribution of elevation points (i.e.
areas where image matching failed) are located primarily at the edges
of each elevation model as well as in areas with steep relief and dense
forest vegetation (Fig. 3). In contrast, the elevation points are dense
and evenly distributed throughout the landslide area and its
surroundings (Fig. 3). Therefore, a lower degree of interpolation was
required and higher accuracy was achieved in the area of interest.
After inspection of the elevation points, the accuracy of DEMs was
evaluated using check points. For this purpose, accurate (±0.015 m)
coordinates of thirty stabilized pillars of the geodetic network
installed in the landslide area (and its surroundings) and measured
regularly since 1988 were used. In addition, coordinates of piezometric
wells (measured in winter 1977–78) were used for evaluation of
the 1977 DEM. However, for the 1969 DEM only the coordinates of
seven points located in stable terrain outside the landslide area could
be used.