In order to obtain quantitative data from multi-temporal sets of
aerial photographs, DEMs were created. Firstly, elevation data were
extracted automatically from all time periods by the ImageStation
Automatic Elevation (ISAE). The default correlation size of 5×5pixels
and correlation coefficient 0.75 were set for all cases. Since the ISAE is
not able to extract elevation data accurately in forested areas (Fabris
and Pesci, 2005; Dewitte et al., 2008), these areas were excluded
from ground point extraction (defined as obscured areas in the
ImageStation) to avoid false elevation changes due to higher
vegetation. Subsequently four DEMs with grid cell size of 5 m
(recommended by the software as optimal) were generated from
captured elevation data. The quality of all the DEMs created was
evaluated using check point statistics (Section 3.3). Then elevation
changes between successive time steps were modelled by DEM
subtraction and profile construction using ATLAS DMT software