pression of
timber, the
on of graz-
his domain.
stands, and
coming to
anagement,
nd growth.
7 specialists
th 2), Once
ment plans
d is of pri-
ficult duty
interpreta-
0; Bercaw,
ll be deter-
, must next
d. Finally,
ded.
art. [Their
author has
tasca State
nnesota. In
an attempt
rest mana -
ecifications
opographic
factory for
hotograph,
rint mate-
his source.
established
as recom-
t of photo-
subsequent
tried expe-
| (Mignery,
, New York.
76 pp.
nal Congress
1951). Rectangular negative sizes have proven unpopular because of the shorter
distances required between camera stations and the resulting lesser exaggeration of
the third dimension in the stereoscopic image.
At the close of World War II, the 1 : 20,000 scale widely used by the U.S.
Department of Agriculture was almost standard for forestry work. The recent
trend has been toward larger scale photography, with 1 : 15,840 being currently
the most widely-accepted scale. This scale has the advantage of being easily con-
verted into the English system of linear and area massurements (4 inches to the
mile, 1 square inch to 40 acres), and is large enough for reasonably accurate
photo-interpretation without being too small for economy. In intensive forest ma-
nagement, however, still larger scales are desirable. [In the Itasca management
study, a scale of 1 : 12,000 was adopted. For the square tract of 50 square miles,
approximately 100 exposures were needed. Larger scales would have required too
many exposures for efficient and economical handling].
At all scales, the tendency is to use the shortest focal length lens commen-
curate with the scale and the topography. Thus, the maximum stereoscopic effect
can be obtained, and the recognition of forest sites and stand size classes can be
facilitated. The 8'/,-inch lens, standard for most forest photography, was used on
the Itasca project].
Both panchromatic and infrared photography are widely used. Since the in-
troduction of modified infrared photography for forest-interpretation by the
writer in 1945, it has become standard for summer photography of mixed conifer-
hardwood regions. At least 100,000 square miles were photographed in 1951 (per-
sonal communication, Eastman Kodak Co., July 24, 1952), and several times that
area have undoubtedly been covered since 1946. Most of this photography has
been for forestry purposes in the southern pine region, the Lake States, and the
Northeast. At least one large infrared project in the Pacific northwest was highly
successful. The value of infrared photography for Canadian forest conditions has
recently been confirmed (Schulte, 1951).
Panchromatic photography also continues to be widely used. It is especially
desirable for large-scale photography under all conditions, for photography when
deciduous foliage is in autumnal or vernal coloration, and for pure coniferous and
pure hardwood regions (Le. not mixed conifers and hardwoods). In the Itasca
management survey, panchromatic photographs were adopted.
The reflectivity of foliage under controlled laboratory conditions has been
reported upon in a series of recent papers (Backstrom and Welander, 1948; Gates
and Tantraporn, 1952, among others). The tone of various tree species on aerial
photographs, however, is due to a whole series of factors of which spectral reflec-
tivity is only one (Spurr, 1948; Schulte, 1951; Losee, 1951). The intensity of the
various wave-lengths of sunlight reaching the tree; the angle of incidence of the
sunlight; the angle of refraction with relation to the camera station; the structure
and arrangement of the tree foliage; and subsequent processing of the film all
affect photographic tone. To note but one example, tone distinctions on infrared
diminish from northeastern to southeastern United States, apparently because the
greater angle of incidence of the sun in the south results in more visible radiation
reaching the tree and being reflected back to the camera. Southern infrared photo-
graphy, however, still provides greater tonal contrasts between tree species than
does comparable panchromatic photography.
