PHOTOGRAMMETRIC ENGINEERING 
CANADA 
According to the information obtained, the 
Forest Inventories Section of the Department 
of Northern Affairs and National Resources 
was in recent times occupied particularly with 
the following research projects in photo inter- 
pretation. 
Data were collected from 290 sample plots 
on the Slave and Peace Rivers to prepare 
volume tables that will assist in the interpre- 
tation of aerial photographs for estimating 
timber quantities. The tables are mainly for 
use with aerial photographs where average 
tree height, canopy density and cover type 
are correctly interpreted, but they may be 
used also for making broad timber estimates. 
Research was continued on the use of different 
air cameras and films for photographs that 
will permit greater accuracy in tree measure- 
ment, and will facilitate the identification of 
species. Sharpness in the air photograph is 
difficult to maintain due to camera vibration 
and the forward movement of the aircraft. 
Photographs were made at a scale of 170 feet 
to one inch (1:2040) taken by a camera 
equipped with a focal-plane shutter. Diffi- 
culties of stereoscopic fusion were overcome 
with a lens of long focal-length. This investi- 
gation was made in cooperation with forest- 
ers of Gillies Brothers and Spartan Air 
Services. More photographs at large and 
medium scales are to be taken and investiga- 
tions are to be continued. 
Conclusions to date are that the standard 
errors of estimate of tree-height measure- 
ments are not less than those which might be 
expected at medium scales, because the base 
of the tree is just as obscure at the large scale 
as at the medium. The greater tree detail, 
however, may well permit counting a greater 
number of trees, an improved measurement of 
canopy density and crown width, and a better 
recognition of species. Also it is possible that a 
better determination of the average height of 
the trees and a suitable index of the height of 
the stand can be secured. 
Efforts are being made to determine cor- 
rection factors for canopy density based on 
the varying parts of tree crowns visible in the 
vertical air photographs in relation to the 
amount of image displacement in order to im- 
prove the accuracy of such estimates. Crown 
densities are apt to be overestimated towards 
the photo edges as there tree crown appear 
more cone-shaped. The object is to determine 
the variation in the area of the crowns ob- 
served stereoscopically and to establish cor- 
rection factors. 
Experiments with camouflage detection 
film suggested that this film might be used to 
indicate vigour of tree stands, as tone in con- 
ifers varied according to the amount of new 
foliage and chlorophyl activity. Infrared 
photographs also show differences in chlo- 
rophylactivity, but wereless useful for the de- 
tection of dead foliage and the recognition of 
species. Paper prints made from Aero Ekta- 
color film proved to be most useful, as addi- 
tional prints could be made from the negative. 
Estimates of costs of this new type of air 
photography are not yet definite, but at least 
the cost of processing will be several times 
that of black-and-white photographs. How 
far these extra costs will be compensated by 
improvement in interpretation, is however, 
not indicated. 
[n close connection with the research into 
possible improvements of the quality of 
aerial photography in relation to interpreta- 
tion, more detailed studies are being con- 
ducted concerning the natural characteristics 
of the tree species. For this purpose a study of 
phenological features, such as occurrence with 
respect to site, branching habit, shape and 
size of crown, arrangement, colour, and de- 
gree of glossiness of the leaves is being made. 
Coincident with improved techniques and 
methods of air photography and forest in 
ventories are demands for new and improved 
equipment for field sampling, air photo-inter 
pretation, and forest mapping. The relascope, 
measuring devices for forest canopy, and 
other equipment were tested. 
The Surveys Division of the B.C. Forest 
Service continued its work in photo mensura- 
tion by the development of a provisional 
volume table for mature coniferous and im- 
mature coniferous forests of the South Coast 
of B.C. For this purpose stand volumes meas 
ured in the field were estimated by means of 
41 multiple-regression equations based upon 
ground- or photo-measured stand variables. 
Five variables, 19 interpreters, 5 stands, 2 
kinds and 3 scales of photos, and 4 different 
finishes of photos were assessed by means of 
correlation coefficients and the portion of the 
total variation in volume removed by each 
variable. Two of the interpreters worked on 
most phases of the project. The main study 
was based upon 15 plots near Haney, B.C. in 
a 40-acre block of young Douglas Fir, hem- 
lock, and cedar. Form of the volume equa 
tion was investigated and local equations 
were compared with standard volume equa 
tions and volume tables. It was concluded 
that the interpreter himself is the most im