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Transactions of the Symposium on Photo Interpretation

cost is only a small part of the total cost of aerial photography. When aircraft
costs, and stand-by time for the flight crew, elimination of the need for prints
and the ease of interpreting color film in rolls are considered, the extra cost of
the color film is minor. Increased interpretation accuracy on color film would
counter balance any slight increase in cost.
Even though the color film used in this test was slightly overexposed, results
showed it to be superior to panchromatic for tree species identification.
In using Munsell color charts it was found that photo scale influenced the
hue that interpreters designated as being the same species. For example, when
these charts were used trees were called greener at the small scale and yellower
at the larger scales.
Tree species were identified accurately enough on the large scales of color
film to suggest the possibility of using them on actual inventory problems.
Further study of hardwoods, especially to associate their crown and foliage
characteristics with physiographic features, should be helpful in the more
accurate identification of these tree species.
Mr. Le Ray (France) asked what method was used to measure the accuracy of the inter
preters. Answer: The analysis of variance.
Mr. Heller answered Dr. D. A. Francis (U.K./FAO) on a relevant question that the costs
of large scale colour photography were five times as high as those of panchromatic photo
graphy. Asked about the operational difficulties the speaker said that flying was carried out
in the morning in order to avoid too much turbulence.
Mr. Hempenius (Netherlands) asked if the time needed for the interpretation of colour film
was less than for panchromatic film. Answer: Interpretation of the characteristics is quicker
on colour than on black and white.
Dr. G. Hildebrandt (B.R.D.) asked if comparable tests were carried out with smaller scales,
e.g. 1 : 15,000. What were the results? Answer: Smaller scales gave no acceptable results for
forest insect damage. The method used is a sampling method and is not meant for mapping