21 
as the studied ones. Every sample plot ought to be localized to a flat 
part of the ground in order to simplify the stereoscopic height mea- 
surement. 
The cruise lines could be thinned according to the sample plots. 
A. good result of photointerpretation is highly dependent on the qua- 
lity of the aerial photographs. A negative scale of 1:20 000 therefore 
seems to be rather small. 
The helicopter used was Bell 47, with seats for driver, the land 
surveyor and the forester. The flying height was 20—100 metres 
and the speed about 30 km per hour. The possibility of controlling and 
completing the mapping out and the site determination was rather 
good. Tree species and stand boundaries could be estimated better from 
helicopter than from ground. It was however more difficult to estimate 
forest site, forest type and soil type from helicopter. 
The flying speed ought to be lower. The noise of the motor was 
disturbing. It was hardly possible to discuss a question without shou- 
ting. The work in the helicopter was mentally hard, as every informa- 
tion had to be controlled and noted practically instantaneously. There- 
fore ıt was necessary for the surveyor and the forester to make a 
short pause of work and to rest once an hour. 
The most valuable experience of this work however is the following 
comparison between the costs of the photointerpretation-helicopter- 
method and the caluculated values of the old field-method. The compa- 
rison can be stated in the following way. 
The new method Cost 
Sw. crowns 
per sq.km 
Field work before photointerpretation .............. 25—44 
Photointerpretation in mirror-stereoscope ............ 10—22 
Control from helicopter «..... eee oorr tnl 6—9 
'Total cost 41—75 
The old method 
Mapping out by generally used field method .......... 340—620 
Land appraisal by generally used field method ........ 110—320 
'Total cost 450—940 
Details concerning this comparison are not given here. Finally it 
must be stated that the conditions in this case are favourable for the 
new method. The difficulties of using this method will likely be greater 
when studying forested areas with dense stands and strongly varying 
forest sites. However the economic advantage of the new method seems 
to have been stated with a satisfactory margin. 
[t is obvious that the new method is possible to develop further, and 
the way to do it is to make new investigations.