= 1390 - 
— Geodynamic phenomena. Processes of mass movement, erosion and 
  
deposition can be recognized from their morphological expression and 
their position in the landscape. The size of the recognizable and 
mappable features is directly related with the scale and the 
resolution of the photography. 
Karst phenomena can be detected from details in the drainage system 
(undrained depressions) and from such morphological features as sink- 
holes. Active faulting can be detected where recent deposits are 
influenced by faults in the underlying bedrock, causing irregularities 
in the morphology and/or the internal drainage and/or surface drainage. 
For the recognition of recently active fault systems a special 
technique, the so-called "low sun angle photography" can be applied. 
Here patterns of linear shadows may reveal otherwise invisible 
morphological lineaments (15). A limitation of this technique is that 
only lineations striking roughly between NW and NE can be detected. 
4.3 Use of photography during the different stages of an engineering 
project 
  
During preliminary investigations aerial photography can be used to 
  
combine and extrapolate the available information on regional geology, 
presence of quaternary materials, and areas of large scale erosion or 
mass movement, 
Planning of the following reconnaissance investigations is facilitated 
considerably, because the areas of special “uterest can be selected on 
the aerial photography. The synoptic view sables a rapid determination 
of all areas that can be excluded from any further investigations. 
For optimum use of aerial photography in reconnaissance investigations 
special photography should be flown of the areas covering the alternative 
project locations. Such photography should preferably be of a scale 
equal or up to twice as large as the mapscale required for this stage 
of the investigations. To prevent excessive relief displacements it is 
strongly recommended to enlarge the photoscale not by decreasing the 
flying altitude but to use camera lenses with a longer focal length in 
such way that the flying altitude remains at least a factor 10 greater 
than the height differences in the terrain. 
This stage of a project offers the best conditions for the application 
of orthophotography. Cost of the preparation of orthophotography with 
printed-on contourlines is of the same order of magnitude as for well 
annotated topographical contourmaps. Stereo orthophotography has still