ich 
sur- 
and 
r to 
p of 
  
PHOTO INTERPRETATION PICTURE, COLWELL 97 
Figure 4, there are four factors which are of primary importance in governing the photo- 
graphic tone of a surface: (A) Light reflectance of the surface; (B) Light sensitivity 
of the photographic film; (C) Light scattering by atmospheric haze; and (D) Light 
  
f, 
Fig.5. Another illustration of the value of multiband spectral reconnais- 
sance. In this instance the objective is to map hydrographic conditions in a 
coastal area. Note that the panchromatic photo on the left is preferable for 
distinguishing fine details in most of the land areas. Such photography is 
therefore preferred for making position determinations, as required for 
establishing an aerotriangulation net to control the hydrographic chart. 
Note that the panchromatic photo also shows underwater details to a great- 
er depth. The infrared photo on the right, however, is preferable for accu- 
rately delineating the line of demarcation between land and water. A third 
aerial (color) photograph is preferred to either of those shown for outlining 
chanels and shoals and for preparing preliminary underwater contour lines 
or form lines. Under favorable conditions the color photography permits 
observation of underwater details to a depth of sixty feet. (Theurer, 1959). 
(Photo courtesy U.S. Coast and Geodetic Survey.) 
transmission by the photographic filter. A study of the light reflectance curves, as deter- 
mined with a spectrophotometer for the four surfaces in diagram A of Figure 4, shows 
that there probably is no single film-filter combination that will give a unique photo- 
graphic tone for each of the four surfaces. Therefore, using the concept of multiband 
spectral reconnaissance in its simplest form, two film-filter combinations are selected 
(panchromatic film with 25-A filter; and infrared film with 89A filter) in an attempt 
to get the tonal values predicted in the table immediately below the four diagrams of