some Investigations about Film and Filter Questions in
Aerial Photography | ~~: anaice
by ¥
to the INT. ARCHIVES OF
~~ ~~ ATE . 73 : >
DIL TOCPAMMETRY Vol X ^54 10RhRA
IVSNSZSNORNZV-- MA IA Ol. ZVXii jn MM
Helmer Bheketrüm, iiL EH
In recent years the interest for the use of aerial photo-
graphy for foresiry purposes has been great in Sweden and a good
deal of work has been made in this domain. At the Photographic
Department of the Royal Institute of Technology we have especial-
ly concentrated upon the photographic problems in this connecti-
on and posed us the question at what time of the year the photo-
graphing ought to take place and which kind of film and which
filter ought to be used so that ihe aerial photographs will dif-
ferentiate in the best possible manner between different tree
species, In the first place we have thereby thought of being
able to differentiate stands of trees of the same kind from each
other. Hereby the different stands in the picture also at small
picture scale must be reproduced with different gray-tones, and
the condition for this is that the stands of trees have a differ-
ent light remission. In order to obtain a starting point for the
discussion of these questions, a series of measurements of the
remission power for diffuse light of different wave lengths for
leaves and needles of different Swedish tree species was begun
in 1947. The measurements were made with Beckman s spectrophoto-
meter and comprised the whole visible and the lower infrared
spectral range up to about 12000 À. The result of these measure-
ments was published by H.Bäckstrôr and E.Welander in 1948 and
1953. In the latter paper the influence of a multitude of dif-
ferent factors on the remission power was investigated. In the
present paper the consequences from this will be taken into con-
sideration when chosing film and filter for obtaining the great-
