High Spatial Resolution Digital Imagery
As described above, flying conditions were good (full sun and light winds).
However, the decrease in aircraft altitude reduced the pixel dimensions (i.e., in-
creased spatial resolution) and, more importantly, decreased the image footprint
(i.e., the surface area captured within a single frame). The lower altitude did not
adversely affect frame "endlap" (overlap between consecutive frames along a
single flightline) but significantly decreased the "sidelap" (the amount of frame
overlap between adjacent flightlines). The three flightlines covering the four sites
within Marsh Creek and Muddy Creek maintained enough sidelap to adequately
cover the areas of interest. However, the four flightlines acquired over Hell Hook
Marsh contained "holidays" (gaps) between flightlines 1 and 2. A continuous
holiday exists between flightlines 3 and 4 over Hell Hook Marsh (Fig. 41).
Owing to both leaf off conditions and the inclusion of large areas of open
water, the color contrast of the features within the images ranged from very dark
(e.g., water) to very bright (e.g., sand, concrete, healthy pine canopies). To com-
pensate for the relatively low spectral response of these dark features, image ac-
quisition settings included a longer integration time (or slower shutter speed).
The increased integration time led to saturation (glaring) of some of the brighter
pixels. In fact, pixel saturation was apparent during acquisition. However, the
system was set to acquire using a slower shutter speed, assuming that an increase
in image contrast would potentially enhance the spectral differences among the
darker features. Many of the frames displayed some pixel saturation. However,
the overall radiometric quality of the images was acceptable with enhanced color
contrast observed throughout the water, wet soil, and senesced vegetation classes.
The greatest disappointment for the project was the exceptionally poor qual-
ity of the images acquired over Spillway 6 on Poplar Island. The extreme level of
saturation within these images resulted from the highly reflective disturbed soils
associated with construction activities. While not evident during acquisition,
pixel saturation rendered this flightline relatively useless for land cover classifi-
cation. Figure 42 shows both the false color and true color mosaic for the spill-