REPORT OF COMMISSION VII
GVII-69
strip aerial photographs, and difficulties were encountered in evaluating scale
for these photos. Hence, this study cannot be compared with others. Dahl used
f acre plots and worked in Eucalyptus forests of Australia of different vari
ability, which isolates this study from all the rest. Moessner’s study uses tracts
of forests which vary from 40 to 640 acres in size, and applies different tech
niques which isolates his work from comparison with any others.
0 1 1 1 1 1 L_
0 4 8 12 16 20
Photo Scale in 1,000 Representative Fraction
Fi<; 1. Variance of differences between photo and ground volume relative to vari
ance of 20,000 scale for various photo scales.
Recommendations
Until more comparable data become available this rationalization indicates
a logical trend from these studies. Imperfect as it is, this imperfection directs
attention to the need for investigators to take greater caution in their study or
work plans. These plans should consider how others may benefit from their
studies; then their work should be so designed that comparable data are ob
tained. Where the factors are due to natural causes (variability of volume), the
investigator has no control, but for variables such as plot size, photo quality,
paired or unpaired observations, photo interpretation techniques and skills of
the interpreter, the investigator has some control. For these items the investiga
tor should attempt insofar as practical to design the studies so that they are
comparable.
There will be some reluctance by investigators to organize uniform research
methods, but if this is not done much will be lost and the publication of research
results will have reduced value.
This is not be be considered as criticizing past research. Photo interpretation
research is a new and active field. The approach to problems has been hetero
geneous because of lack of organization and experience. In many fields of en
deavor, the great demand, for reliable information about photo interpretation
challenges the investigators. This demand creates more studies. The experience
