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good cameras with very high shutter speeds have become available for forest
surveys. One of the most important developments was the successful use of a
70 mm. Hulcher camera for insect-damage surveys in the United States
[Aldrich, Bailey, Heller, 1959].
A different, but promising approach has been followed by Avery, [1959],
who experimented with large-scale photographs taken from helicopters using
a stereo-mount of two hand cameras, and progress on a similar project is
reported from British Columbia [Lyons, 1961].
The forest mensurational possibilities of 70 mm winter photography and the
availability of an air camera that would provide sharp, large-scale photo
graphs, were recognized by H. E. Seely, Head of the Forest Inventories
Section, Department of Forestry, who recommended that research to control
the “washout” in winter photography be conducted and that a shutter speed
of 1/1000-second be used to minimize image motion. Consequently, early in
the spring of 1961, when much of the ground was still covered by snow, the
Canadian Department of Forestry arranged for large-scale sampling photo
graphs to be taken with a Vinten 70 mm camera, with a lens having a focal
length of 4 inches, and at a scale of 1 : 2400. A preliminary appraisal of these
photographs has been made by Seely [1962].
The photographs were excellent for obtaining qualitative information about
the forest. Such detail as the tufts of foliage of red pine and the small branches
of hardwoods could be seen. White pine, red pine, white spruce, and balsam
fir could be identified with no difficulty by their characteristic crown shapes
and branching habits. Among the hardwoods, both aspen and white birch
were recognized at first glance by the tone of their bark. It was more difficult
to identify other hardwoods but occasionally this was possible for basswood,
maple, and elm.
Due to the excellent image sharpness, it was expected that tree heights,
crown diameters and even stem diameters could be measured on the photo
graphs with an accuracy that approached that of ground surveys. These photo
Fig. 1. Stereogram of vertical, 70 mm photographs (1 : 1200)
