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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
Fig. 8. Super-XX/minus-blue aerial photograph of a forest stand in central Illinois, U.S.A., 
taken at the peak of the fall color change. (Univ. of Illinois photo.) 
between species such as those shown in fig. 8 have provided 95 percent ac 
curacy in genus interpretation and 75 percent accuracy in species interpreta 
tion within the oaks (Quercus). 
The practical possibilities of the fall tonal renditions seem limited by the 
small number of good photographic days available during the two or three 
weeks of the fall color change. In the State of Illinois, it is possible to overcome 
this difficulty by confining aerial photographic flights to the morning hours. 
Our experience has shown that approximately 60 percent of the days during 
the fall color change period have two or more hours when conditions for aerial 
photography are excellent. 
Literature 
1. Olson, C. E., Jr., and R. E. Good. (1961). Seasonal changes in light reflectance from 
forest vegetation. Photogrammetric Engineering, Vol. 28: 107-114. 
2. Sayn-Wittgenstein, L. (1961). Phenologic aids to species identification on air photographs 
Forest Research Branch (Canada), Technical Note No. 104, 26 pp.