xposures, and
e clock. The
aphs worked
otography of
ternal clocks.
elocity -depth
wave length
in a known
photography.
riod is found
stant for the
ths of waves
it wave crest
hallow water
at the change
ntours in the
ed sorties at
of contours
ethod is not
e tidal range.
on on which
an extension
hic mapping.
h determina-
ately on the
le, extremely
f the Sonne
thod requires
low altitude
e to one or
al equipment
| attachment.
Ses.
ical analyses
. at a simple
h across the
measure its
nen on larger
age carefully
oper and the
idth between
le and, based
(689)
on the uniformity of the measurements, on the tone and texture of the roadbed
and the rather regular character of the division between road and shoulder,
identifies the feature as a 20 feet concrete highway. He may then proceed to
make further measurements including slope of road as it leaves the beach, the
dimensions of the bridges it crosses, etc. :
Even in underwater depth determination, where metrics play such a con-
siderable role, the concurrent problem of identifying a shoal area as rock, mud,
or sand exists. Then too, particularly in the parallax methods, careful visual
analysis is required to properly identify masses of floating underwater seaweed
which might be mistaken for areas of shoal rock and so plotted.
Such cases, where both visual examination and measurement contribute
equally to the final interpretation, are more the rule than the exception in
practice.
IV. Uniformity of Techniques.
The amount of variation in the techniques of the amphibious interpreter
from problem to problem is difficult to assess. Because of the large number of
various kinds of features he must study, interpret and record in any coastal
area, he tends to run the gamut of his techniques on nearly every problem.
There are, of course, great differences in coastal areas, and these differ-
ences require a flexibility of approach on the part of the interpreter. Beaches
occur along broad coastal plains, in cove or bayhead areas, at the foot of hills
rising steeply from the shore or at the end of the river deltas. Successful World
War II landings took place under all sorts of climatic conditions from the
latitudes of the Aleutians to those of the Solomons.
This variation persists when details are studied. It is true that beaches, like
other landforms, tend to occur in recognizable types, each of which has some
predictable characteristics. However, in the detailed analysis of beach materials,
and of rock and soil types behind the beach, an infinite variation exists. As Hack
(4) points out in discussing the analysis of geologic features, "What can be
accomplished by photographic interpretation is limited by the knowledge of
the interpreter, however acquired, of the geology and geography of the area
being studied."
These variations, however, do not normally require changes in the actual
physical procedures or equipment used by the photographic interpreter from
one area to another. He still examines the photography stereoscopically, uses
high magnification and measurement on pertinent features, makes inferences
and interpretations from what he sees, and reports his findings. But his mental
processes and his conclusions may be entirely different.
There are, of course, certain techniques which will vary sharply from area
to area. One of these is depth determination. The three principal types of depth
determination methods previously described are widely different in theory,
procedures, and photography required. The environment of the target area
usually dictates the method to be used. The parallax method, for example was
used by Naval interpreters with singular success in the South and Central
Pacific where the combination of transparent water and good bottom detail
was found. Wave methods were used in areas where suitable non-complex wave
patterns were found, while the waterline method was employed in areas where
the tidal range favored its use.
