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Flight
specifications for the NHAP program require that all photographs
meet certain standards regardless of the geographic area involved.
The sun angle is thirty percent or higher to reduce potential
shadow effects on the ground. Cloud cover must be absent, and
atmospheric haze must be minimal. Even seasonal factors such as
the presence of snow on the ground, flooding, or the amount of
foliage are considered prior to accepting the photography. The
center point of each photograph must also fall within a 1,000 foot
radius of a pre-determined position within the north-south flight
lines. Camera tilt shall not exceed four degrees, nor average more
than two degrees, in any ten mile section of a flight, nor average
more than one degree for the entire flight contract.
NHAP photography
was acquired from an altitude of 40,000 feet. Two different camera
systems were used to acquire simultaneous coverage at two
different scales. A 6-inch focal length lens acquired
black-and-white (B/W) film at an approximate scale of 1:80,000.
B/W photos cover a ground area of 11 x 11 miles. An 8.25-inch lens
acquired color-infrared (CIR) film at an approximate scale of
1:58,000. CIR photos cover a ground area of 8 x 8 miles.
The following
print sizes and scales are available:
| Film Type |
Print
Size |
Enlargement |
Scale |
1"
equals |
| Black & white |
9 x 9 in |
1x |
1:80,000 |
6,666 ft |
| 18 x 18 in |
2x |
1:40,000 |
3,333 ft |
| 30 x 30 in |
3.33x |
1:24,000 |
2,000 ft |
| 36 x 36 in |
4x |
1:20,000 |
1,666 ft |
| Color-infrared |
9 x 9 in |
1x |
1:58,000 |
4,833 ft |
| 18 x 18 in |
2x |
1:29,000 |
2,416 ft |
| 22 x 22 in |
2.42x |
1:24,000 |
2,000 ft |
| 36 x 36 in |
4x |
1:14,500 |
1,208 ft |
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