Geoscience Reference
In-Depth Information
Figure 3-15.
Conventional panchromatic (visible, gray tone), vertical, aerial photograph of the Crestwynd vicinity,
southern Saskatchewan, Canada. Part of the prairie pothole region, this area contains countless small lakes and
marshes of variable sizes and irregular shapes. Photograph A21639-7 (1970); original photo scale 1 : 80,000.
Reprocessed from the collection of the National Air Photo Library, Natural Resources Canada.
security reasons and is not available to the
public or scientii c researchers.
A popular trend during the past decade is
conversion of conventional aerial photographs
into digital orthophoto quadrangles (DOQ).
These images have been resampled to remove
geometric distortions and to i t accurately onto
a ground coordinate grid with high pixel
resolution
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usually 1 or 2 m. In the United
States, DOQs are produced in the NAD83 geo-
detic datum and UTM grid projection. Each
DOQ corresponds to 3.75 or 7.5 minutes of
latitude and longitude referenced to standard
7½-minute map sheets (U.S. Geological Survey
2001). DOQs may be utilized for GIS in combi-
nation with other kinds of cartographic data
3.2.4 Meso-level systems
Conventional aerial photographs have been the
workhorse for wetland mapping and investiga-
tions of all sorts since the mid-twentieth century.
These are most typically panchromatic (visible,
gray tones), color, or color-infrared vertical pic-
tures taken from several thousand meters above
the surface at original (i lm) scales of 1 : 12,000
to 1 : 80,000 and spatial resolutions of 1-4 m
(Fig. 3-15; Tiner 1997). In many countries, useful
aerial photographs date back 60 years or more
and represent important historical images for
documenting wetland conditions (e.g. Aaviksoo,
Kadarik and Masing 1997). In some countries,
however, aerial photography is classii ed for
