MARUYASU, NISHIO—ON THE STUDY AND APPLICATION OF INFRA-RED AERIAL PHOTOGRAPHY 3
2. ADVANTAGES CLAIMED FOR AM
INFRARED AERIAL PHOTOS |
We hear that infrared aerial photos were utilized for detecting camouflage during the |
war, but of late they are about to be used for the identification of the variety of trees in E |
the realm of forestry. |
There is a phenomenon called Chlorophyll effect in infrared photos. The light that
reflects from the surface of tree leaves comes out particularly strong in infrared photos and
green looks white and radiant. This is of much help toward identification. On the contrary,
in the case of panchromatic photos a green color is less sensitive to the film than other colors
and it comes out black on the photo. This occasionally made the identification difficult. This
is one of the characteristics of infrared photos.
Generally, light diffuses in inverse proportion to the fourth power of wave length and
becomes diffused light. So such a ray does not extend far. With the prolongation of the wave
length, light reaches farther. Therefore, without being affected by haze which always constitutes
an obstacle when taking aerial photos, we can obtain vivid pictures if we use infrared films.
Since heat ray is absorbed into water, such objects as rivers, paddy field, river system
in the mountains, swampy land and watery soil come out black on the photo and detection of
them on the photo becomes extremely easy.
Generally speaking, among various factors that constitute the standard for identification
on photos, the shape and density of an image are a vital element. There are innumerable
instances in which the object can be identi- ;
fied particularly by the difference in density. Y= tan © T
The ratio of this density is indicated zt d
by the contrast between high light and
shadow. This contrast can be sought from
the characteristic curve of photographic
emulsion (see Fig. 1).
In the case of aerial photos, the con- Underexposed
trast varies according to shooting altitude. ll
When photographed at high altitudes, th
entire picture looks alike in density and the“ f \
characteristics of the picture are lost when 0 i 2 3
we make interpretation. So when develop- |
ing photos taken from a ultra-high altitude: |
a special treatment had to be considered so Fig. 1 Characteristic curve.
as to make contrast more striking.
Overexposed
part
Density
Properly exposed
e part
We took photos at various altitudes simultaneously, using panchromatic aerial film hitherto
in use and infrared film, and developed negatives taken at each altitude in set by the method
Table 1 Lad
Shooting altitnde Danchromatie fm | rires im m | |
Upiog00metes 1... 09... ] d Lido os |
1000-3000 meters 1.3 | 1.8 |
3000 meters E 1.6 2.3 i
