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PHOTOGRAMMETRIC ENGINEERING 
No. 8 and 47 Wratten filters and only records 
reflected light below 460 millimicrons in 
length. Figure 6 was taken with a No. 25 
Wratten filter and only records reflected 
light above 685 millimicrons in length. Be- 
cause the use of more than one photographic 
system would probably be impractical it is 
desirable to combine spectrophotometric 
studies with other methods, such as the use of 
color photographs. This topic is discussed 
further below. 
DENSITOMETRY 
Quantitative measurement of photographic 
tone—either in terms of optical density of 
film materials or in terms of light reflectance 
from paper prints—may be useful in geologic 
research. Frequency of tone changes, as well 
as the magnitude of the tone measurements, 
could be significant in describing terrain fea- 
tures and in permitting comparisons of dif- 
ferent terrain features. Initial studies involv- 
2.275 
Density (photographic tone) 
  
  
| 2 À i i i i À 1 À 1 A J 
0 5 IO cm. 
Length of traverse across film 
(showing frequency of tone change) 
2.0 B 
Density (photographic tone) 
o 
1.2 À À i i 1 À L i À À À i À. J 
o 5 10 15 cm. 
Length of traverse across film 
(showing frequency of tone change) 
FrG. 7. Graphs showing relation of magnitude 
and frequency of tone changes across two glacial 
moraines of different ages. A—older moraine; 
B— younger moraine. 
6 
  
  
  
  
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2 
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AS 1.8 
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= 16 , 
0 5 10 15 cm. 
Length of traverse across film 
(showing frequency of tone change) 
2:67 
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1.6 i 1 J 
Oo 5 10 15 cm. 
Length of traverse across film 
(showing frequency of tone change) 
Fic. 8. Graphs showing relation of magnitude 
and frequency of tone changes across two different 
landforms. 4—alluvial area of low relief; B—g¢la- 
cial moraine. 
ing measurement of frequency and magnitude 
of tone changes across two glacial moraines of 
different ages showed differences that are be- 
lieved significant with respect to the relative 
ages of the moraines. The data, determined 
with a McBeth-Ansco Model 12A densitome- 
ter, are shown in figure 7. Measurements 
across different landforms were strongly dif- 
ferent, as shown in Figure 8, which contrasts 
an alluvial area of low relief with hummocky 
morainal material that included many small 
lakes. 
Moore (1947) used photographs taken 
through color filters in compiling ‘‘brightness 
profiles’’—based on densitometer measure- 
ments— which were used in determining 
depths of water. However, no work of this 
type, employing color filters and densitome- 
try, has been undertaken with regard to land- 
form features. Nevertheless, studies using 
available conventional photographs suggest 
that densitometry may provide data that 
would permit correlations, perhaps of age as 
as well as lithologic composition of geologic 
features, at least within local areas of similar 
climatic environment. Study is continuing, 
not only with respect to obtaining measure- 
ments of specific geologic features but with 
regard to reduction of the quantitative data 
to simple terms for comparing terrain features.