:d the degree 
y large-scale 
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metrics, may 
  
same camera as 
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necessary for 
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he difficulty 
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(693) 
cifications. Low-level, continuous-strip, image-motion compensation, vertical 
photography is used for parallax methods. Smaller scale verticals, precisely 
timed, are used for wave methods. Repetitive timed coverage at various tide 
heights is flown for water level methods. Other methods in experimental stages 
will require still other specifications. 
VIII. Advantages and Limitations of Aerial Photography. 
The vertical aerial photograph provides a complete, up-to-date near-plan 
view of the amphibious objective area. Every visible feature of the area is 
recorded on this view, and is thus available for intelligence use, provided the 
image can be correctly interpreted. This characteristic of the aerial photograph 
is one of its great advantages. 
A second advantage is that the entire related area can be examined at once 
by means of small coverage. It is possible, therefore, to determine on the pho- 
tograph the physical relationship of 
natural and cultural features to one 
another, even though those features 
may be separated by a considerable 
distance on the ground. Frequently the 
photograph will reveal the “why” of 
the conditions that exist. For example, 
a ground observer may note that there 
is a great deal of suspended silt in the 
water immediately offshore of a beach. 
The aerial photo interpreter will not à ing 
only be equally able to identify this Fig. 10. Vertical aerial photo of a river 
silt, but will be able to measure its ex- Miodeh. 
tent offshore and along the beach, and 
probably to trace it to its source in a river mouth several miles up the coast. 
In addition, the photographic interpreter can determine what the direction of 
the current must be in order to carry the silt from the river mouth to the 
beach, a fact which the ground observer may not as easily discover. 
Another advantage possessed by the aerial photograph, is that it makes 
possible repeated observation over enemy-held or otherwise inaccessible areas. 
Furthermore, these coverages can be planned to occur at a desired stage of 
tide, or time of day. During the weeks preceding the Normandy Operations, 
the landing beaches were photographed an average of three times each day. 
Other types of observation of enemy-held areas usually require occupation of 
the area by an observer, and can be made only once or twice during a normal 
planning period. 
Finally, the photography “freezes” a scene - something which other means 
of observation normally cannot do - and brings it back to the expert who is 
most qualified to interpret it. The photograph thus obtained can be used over 
again, for comparison with earlier and later views and with other sources of 
intelligence. And each time the camera’s original, unbiased impression is avail- 
able. 
Aerial photography has also very definite limitations as compared with 
ground observation. The photographic interpreter can never provide as much