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ERDC/CRREL TR-02-11
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IMAGERY EVALUATION
Area 1 sites
Sites 1, 2, and 3 are located in the area 1 mosaic, constructed using 3-ft GSD
imagery, as shown in Figure 3. The state of roof conditions will be examined
from the high-resolution imagery for sites in area 1 that have been designated
with a yellow boundary marker. Site 1 has a house with exposed roof rafters, and
site 2 has a house with plywood roof sheathing in place that is mostly covered
with tarpaper. Site 3 has a house with exposed roof rafters, but the electronic
camera sensors saturated as the image was acquired. Saturation is a problem in
image acquisition that occurs when the gain is set too high for the target of
opportunity. In these images, the rafters were at the white end of the brightness
range and sometimes disappeared into the uncovered concrete substructure of the
building, which was also bright. This resulted in permanent data and detail loss at
the white end of the brightness range.
House roof rafters
Figure 4a shows site 1, a house under construction with exposed roof rafters
in the lower right corner of the image, at 2-ft GSD. The detail is barely sufficient
to distinguish individual roof rafters at this GSD. At both 1-ft GSD (Figure 4b)
and 8-in. GSD (Figure 4c), however, the same site shows sufficient detail and
resolution to distinguish individual rafters. .
Tarpaper/shingles/plywood
Figure 5 shows site 2 at 8-in. GSD. A new house without roof shingles is to
the left of the center of the image. Part of the roof is covered with tarpaper and
part is covered with plywood. Resolution and detail are not sufficient to detect
the edges of the tarpaper or shingles that would distinguish one from the other.
The tarpaper strips are 3 ft wide by as long as the roof is wide, and the shingles
are 3 ft wide by 1 ft high. Contrast between the roof covered with tarpaper and
that sheathed with plywood, however, is visible at this and greater GSDs.
Saturation problem
Figure 6 shows site 3 at 1-ft GSD. A new house in the middle of the image is
under construction, but due to sensor saturation at the high end of the intensity
(or brightness) scale, individual roof rafters are obscured. This is because bright
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