NTORY OF TERRAUTN CLASS 
ORTIONS DIRECTLY ON THE 
S OF PHOTO -OR OT HER 
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Tr IMAGERY 
Dr. Simo Poso 
University of Helsinki 
Unioninkatu 40B 
SF-OO170 Helsinki 17 
Finland 
Introduction 
The natural resources, forests, agricultural land, etc. are 
usually in good correlation with topographical features. This 
correlation means that a sampling for the inventory of natural 
resources must be unbias in respect of terrain classes. 
The bias is not a great problem when sampling is made on 
topographic maps or on other orthoprojectional medium. Problems 
arise when aerial photos or other remote imagery are used for 
sampling and inventory purposes. The scale of photos varies 
from a point to another. This is why it has been concluded 
that the photo basis is not applicable to drawing a sample 
for an inventory, or it is necessary to apply an adjustment 
procedure for correction of results (Loetsch and Haller 1964). 
The objective of this article is to work with this problemacy 
and to show that it is possible to get estimates for area- 
class proportions without bias also when the sampling is made 
directly on the basis of aerial photographs, or other remote 
imagery. 
Basic idea for sampling 
  
For reasons of simplicity it is assumed that aerial photo- 
graphy is made according to systematic sampling for inven- 
tory purposes. This means that the distance from one photo 
to another should be according to systematic design in respect 
to field measures. This requirement is usually reached with 
sufficient accuracy when an automatic timer is used in flying 
at constant velocity. The systematic sampling should be re- 
garded as if it had been taken with random start.