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sampling areas was obliterated 48 hours prior to the photo mission and actual 
sampling for population estimates by ground sign-counts. The "natural" 
plots were left unmolested to determine if new versus old sign could be discriminated 
in the aerial photographs, and thus avoid the need for sign obliteration in 
subsequent operations. All ground counts for gopher sign were made within 
two hours of the photo mission. At the time of the ground counts, the location 
of all new and old sign was plotted on a map of the subplots. 
In addition to the gopher sign ground-counts, vegetation was sampled 
on the subplots for the amount of tall (> 15 cm) and short (< 15 cm) material 
to determine if relative vegetation height had an effect on photo-counts of 
gopher sign. Vegetation was sampled by line intercept (Canfield, 1942) using 
two transects, each 7.13 m long, oriented at right angles to each other in 
each subplot. These measurements were completed during the 72-hour period 
immediately prior to the photo mission. Also, ground photos were taken the 
day of the photo mission to assist in interpretation of aerial photographs. 
Aerial Photography 
Aerial photographs were obtained at two resultant scales — 1:600 
and 1:1200 — on August 31, 1971 between 1730 and 1820, Greenwich Mean Time. 
Photos were taken from a U.S. Forest Service Aero Commander 500-B using 70 mm 
Maurer KB-8A cameras equipped with 150 mm Schneider Xenotar lenses. 1 
Two film types were used: (1) Kodak Aerochrome Infrared - Type 2443 
and Kodak Ektachrome Aero - Type 8442. A Wratten No. 12 filter was used 
with the color Infrared film; no filter was used with the color film due to low 
(100 m and 200 m) flying altitude above ground and minimum atmospheric haze. 
Two cameras were used and pulsed simultaneously with a common intervalometer. 
The films were cycled to obtain at least 60 percent overlap for stereo-interpretation. 
Weather at the time of the photo mission was clear with at least 100 kilometers 
visibility. 
Ground markers were used to designate the corners of the major plots 
and the center and edge of the subplots. White wooden laths 2 m long were placed 
at right angles to each other at the corners of the major plots. White paper 
plates were used to designate the centers of the subplots; a piece of the white 
lath was placed tangent to the edge of each subplot to designate its edge. Red 
and white flight line markers 3 m long were placed 100 m outside the edge of each 
plot to designate flight line direction and length and provide control for 
photo scale determination. In addition, white surveyors stakes 5 cm wide by 
30 cm long were used to designate the location of new and old gopher sign. 
These markers were placed away from the subplots but within the effective imaged 
area of the aerial photographs. 
1 Trade n am es and commercial products are mentioned for the benefit of the reader 
and do not imply endorsement or preferential treatment by the U.S. Department of 
Agriculture.