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SYMPOSIUM PHOTO INTERPRETATION, DELFT 1962 
Die Ergebnisse zeigten, dass bezeichnenderweise mehr Baumarten im Farbfilm richtig be 
stimmt wurden, als im panchromatischen Film. Wie erwartet, lieferte der grösste Masstab die 
grösste Genauigkeit, aber nur wenig Verbesserung konnte zwischen den Masstäben 1 : 1584 
und 1 : 1188 erreicht werden. 
Bei der Untersuchung der Farbbilder ergaben sich keine Genauigkeits-Unterschiede zwischen 
den fünf Auswertern, aber wohl war dies der Fall bei der Betrachtung der panchromatischen 
Abzüge. Die Genauigkeit der Interpretation belief sich auf 81% (Mittelwert) auf den Farb 
bildern des grössten Masstabes. Diese vielversprechenden Ergebnisse scheinen weitere Nach 
forschungen genügend zu rechtfertigen. 
The U.S. Forest Service does research in the techniques of aerial photo 
graphy and photo interpretation in order to increase the efficiency of a variety 
of projects, including a nationwide forest resource survey and timber inven 
tories for management planning on national forests. One rather fundamental 
research study is discussed here, the purpose of which was to improve the 
recognition of individual tree species on aerial photography. Results of this 
study should be applicable not only to inventories of timber but also to other 
projects as well - such as those to assess damage to forests by destructive 
enemies, to appraise forest wildlife habitat and to help expedite forest admini 
stration. 
Procedure 
Area and species involved 
This study was conducted in northern Minnesota near the Canadian border 
to determine the best film and scale combination for identifying tree species. 
The terrain is rolling and was previously glaciated. Forests cover about 85 
percent of the land area. 
Fourteen important tree species were selected on 29 separate locations. 
Nineteen replicates were taken on eight of the most important species and fewer 
replicates on the other six species. All locations were picked in such a way that 
physiographic features would not aid the interpreter in identifying individual 
trees. 
Collection of ground data 
Trees were identified in the field on large scale (1 : 1000) black and white 
stereoscopic prints made from color transparencies. (Since this study, a portable 
battery-powered light table was developed for field use to locate objects on 
the color transparencies.) 
A detailed description was made of each tree. This included species, D.B.H., 
height, crown class, site class, and other associated features. Species were 
located randomly over as many sites as possible. Only dominant, co-dominant, 
and intermediate trees were included since overtopped trees are not visible 
from the air. 
Collection of air data 
A Hulcher 70 mm camera having a 150 mm focal length was used. It can