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LETT P eem ns 5
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
e A
2
vo 2.0
CE
ce V^
AS 1.8
o
o
=
= 16 ,
0 5 10 15 cm.
Length of traverse across film
(showing frequency of tone change)
2:67
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c
e
o 24 B
2
a
9
wv 2.2 |
o
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a
~ 2.0
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3 18
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.