TM 5-852-2/AFR 88-19, Vol. 2
Sioux Falls, South Dakota, probably contains the
oblique and vertical photographs are most com-
most comprehensive inventory of aerial imagery in
monly used. Low-altitude obliques are useful for
its data bank.
evaluation studies and illustration. Vertical stereo-
(2) A number of techniques are used to indicate
pairs greatly aid terrain interpretation.
(2) Focal length of lens. A lens with a short
and identify what particular aerial photograph
covers what particular area. A common method
focal length should be used in flat areas to increase
used by the USAF and a number of other
the apparent depth perception in the stereoscopic
government, as well as commercial, agencies is the
image so that minute changes in relief are resolved.
"flight line map." The centerlines of strips of aerial
A 6-inch lens is recommended. In hilly or
photography are drawn on a base map, with the
mountainous terrain, a 12-inch focal length lens is
photo mission, date, scale, emulsion and camera
most practical.
(3) Type of film. Panchromatic (black and
specifications usually annotated as part of the
legend. Usually, the ends of each flight line are also
white) film is widely used for a basic photo
annotated with film roll number and exposure
coverage. Color aerial film and color infrared film
number. By use of a flight line map that covers the
are being increasingly used, especially over selected,
area of interest, the exact exposure numbers can be
environmentally sensitive areas. Color infrared film
identified to place an order for photographic prints.
is normally used to produce positive transparencies
(3) A second method uses a "photo index sheet"
rather than paper prints.
(4) Types of filter. Filters are used to cut
where all of the aerial photographs taken of an area
have been roughly pieced together with all exposure
atmospheric haze and to accentuate tonal differ-
numbers showing. This mosaic is photocopied and
ences. Yellow haze filters, often referred to as
reduced to a convenient size (the U.S. Department
''minus blue'' filters, are used with both panchromatic
of Agriculture uses a 20- by 24-inch size), which
and black and white infrared films.
(5) Overlap and sidelap. Photography intended
can be used to order the aerial photographs
required.
for use in mosaics and for detailed stereoscopic
(4) A third method, becoming more common, is
interpretation should have a 60 percent overlap
conveying all aerial photography information
between frames along a flight line and a 30 percent
through a computer printout. This method is parallel
sidelap between flight lines.
(6) Location. Geographical coordinates bound-
to the previously illustrated method of ordering and
determining satellite imagery coverage. In this
ing the area should be indicated. Flight lines plotted
instance, a search is made by the EROS Data Center
on large-scale topographic maps are of considerable
for specific airphoto coverage of an area based on
value to the aerial photographer. If possible,
geographic coordinates. Upon the completion of the
checkpoints should be established on the ground to
search, a computer printout is received and the user
aid the aerial photographer.
(7) Scale. The scale of photography is normally
can select his photo.
(5) To ascertain the coverage of certain photos
specified in terms of the representative fraction
listed on the printout, a rough flight line coverage
(RF), which is equal to the flying height (in feet) of
overlay should be developed on a suitable base map.
the aircraft above mean terrain, divided by the focal
This process is illustrated in figure 3-4, where the
length (in feet) of the aerial camera. For example,
data have been transposed into a photo coverage
the scale of photography flown at 6,000 feet with a
overlay based on a 1:250,000 topographic map.
6-inch lens is 1:12,000. For regional coverage and
Since, in this case, the computer printout had
analysis, scales of 1:40,000 to 1:80,000 are
indicated each corner covered by a strip of
recommended. For local, highly detailed analysis,
photography, the overlay has been constructed to
scales as large as 1:10,000 to 1:20,000 are useful.
(8) Season for photography. Usually, the sum-
show the total area covered by each flight line as
well as all the flight lines needed to cover the
mer season in arctic areas is specified because of
desired area.
extended daylight and a lack of a snow cover in
b. Acquisition of new aerial photography. Quite
most areas.
(9) Annotation of negatives. Every aerial pho-
often it is desirable, and at times necessary, to
acquire new aerial photography either to supplement
tograph should be annotated with at least an
existing photos or in case no suitable existing aerial
exposure number. Each end photo of a flight line
photography can be obtained. In requesting new
should be annotated with roll number or line
photography the following items should be
number, scale, and date. To adequately control
considered.
numerous aerial photography projects, a project
(1) Types of photographs. Nine- by nine-inch
symbol should be annotated on each photo.
3-6
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