PHOTOGRA 
  
TETRIC ENGINEERING 
  
During the war infrared film was used in detecting camouflage, partic- 
ularly dead vegetation. It was natural that foresters should try this film asa 
means of recognizing forest species. A modified infrared film (Figure 1) has 
been used to separate conifer and hardwood species particularly in the North- 
ast and Lake States areas of this country. But even this has serious de- 
ficiencies and sometimes indicates identical tone for worthless dead vegeta- 
tion, wet swamp, and valuable stands of young conifers. 
At present some foresters are enthusiastic about color film and see in 
color transparencies a means of recognizing species, provided the film can be 
reduced in cost, and practical means devised for using the transparencies 
outside the laboratory. However, the same differences in tone due to direc- 
tion of the sun and shadow are present in color as in panchromatic or infra- 
red film and may prove equally baffling to the interpreter. In fact we find 
that in areas of low relief, panchromatic film (Figure 2) flown in spring when 
hardwood foliage is new or in the fall when foliage is turning, will give tonal 
  
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FrG. 3. Stereogram illustrating correlation between forest and soil types. (1) Upland soil 
supports one forest type, (2) bottomland soil supports a different forest type, and (3) soil scientists 
type line indicated by difference in photographic tone of the bare ground coincides exactly 
with the foresters’ type line indicated by the difference in tone of the forest cover.