WORKING GROUP 4 
SAYN-WITTGENSTEIN 
259 
is generally less turbulent. On the other hand, it is more difficult to position 
flight lines from high altitudes, because of difficulties in navigation and because 
the slightest tilt will cause photographs to deviate considerably from the 
planned flight line. As the investigation of the 1962 photographs is not yet 
completed, the final answers are not known at this time. 
While the current work of the Forest Inventories Section deals primarily 
with vertical, panchromatic photographs, experiments with other special 
photographs are also in progress. For example, oblique photographs were taken 
at large scales. These photographs resolve clearly the stem and the branches 
of the leafless hardwoods and the sides of the crowns of conifers (fig. 2). Tree 
species are more easily identified on obliques than on verticals, and obliques 
have potential values for the measurement of stem diameter and tree form, 
but, it is more difficult to determine the scale of obliques. On several occasions 
colour photographs were taken; at first with Aerial Ektacolor film at small 
and intermediate scales, and more recently at large scales with Super 
Ansochrome. 
We have no evidence that colour photographs are better for taking meas 
urements, but they make species identification easier, particularly on photo 
graphs taken shortly after the leaves of deciduous species have come out. The 
young leaves of many hardwood species show characteristic colours that help 
to distinguish them from other species but often these differences disappear as 
the leaves mature. Also, a few hardwood species that could not be distinguished 
on panchromatic photographs taken during the winter could be distinguished 
on colour photographs. For instance, we found it possible to distinguish be 
tween trembling aspen (Populus tremuloides) and largetooth aspen (Populus 
grandidentata), because the former has greyish-green bark, while the latter’s 
bark has an orange tinge. Colour photographs are also better if one is concerned 
with finding trees that have been attacked by insects and diseases. 
Tests of large-scale, infra-red photographs have not been made. Unless such 
photographs are useful for forest disease surveys, they probably have no ad 
vantages, because the separation of hardwoods and conifers is a simple matter 
at large scales. 
Among the most spectacular sampling photographs tried out by the Forest 
Inventories Section are camouflage detection photographs, which make it 
possible to distinguish healthy foliage from that which is dead or diseased. 
Plans have also been made to take large-scale camouflage detection photo 
graphs during the winter, but the necessary film has not yet been obtained. 
From all these experiments it is concluded that large-scale sampling photo 
graphs will play an important role in future forest surveys. Today much 
qualitative information can be obtained from such photographs, but important 
problems have yet to be solved before reliable measurements can be made. 
References 
Aldrich, R. C., W. F. Bailey and R. G. Heller (1959). Large scale 70 mm colour photo 
graphy techniques and equipment and their application to a forest sampling problem. Photo- 
grammetric Engineering Vol. 25, No. 5.