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PHOTO INTERPRETATION PICTURE, COLWELL 107
photographs, for until they do they will continue to misinterpret many objects and con-
ditions, often without ever realizing how seriously they are in error.
4. Photo interpreters should better understand how to make measurements on aerial
photographs.
While this need can assume many forms, perhaps two examples will suffice to illus-
trate the point.
a. Figure 13 shows a portion of the Lituya Bay area in West Central Alaska. Quite
apart from the main point to be made here, this photo clearly documents an almost un-
Fig.13. Oblique aerial photo of a portion of Lituya Bay, Alaska shortly
after the shoreline had been swept by a gigantic wave which washed away
timber to a height of 1720 feet at point E. For examples of the various types
of erroneous measurements sometimes made by photo interpreters on oblique
photos such as this, see text. (Photo Courtesy U.S. Geological Survey.)
believable event. Shortly before the photo was taken, a tremendous quantity of ice and
rock fell into the upper end of the bay in the vicinity of the point *X". The initial wave
of water generated by this phenomenon surged up the far side of the bay to the point
*E", washing away all of the forest trees between *E" and the present waterline. The
remarkable fact is that “E” is 1720 feet above “B” (Miller, 1959); without this photo-
graphic evidence few people would believe that such a wave could be generated. (Note
also that a secondary wave has removed trees all along the shoreline to a height of
several hundred feet, as it sped down the bay.)
Returning to the problem of photo measurement, let us assume that, given the above
information, the photo interpreter wishes to measure the distances “AB” and “CD”.
While such measurements can be accurately made when two or more oblique photos of
the same area are available, few photo interpreters would know how to make the meas-
urements and perform the subsequent calculations. And, alas, some photo interpreters
DFE UME EEE ga ^ —
