High Spatial Resolution Digital Imagery
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7.5
Utility For Arcview Application for Enhanced Levee Inspections
Both sets of CAMIS mosaics were provided to the District for evaluation in
assisting levee inspections. Their review was based primarily on the ability of the
1-m multispectral mosaics to provide useful information for the inspection proc-
ess. Their conclusion was that the spatial resolution would need to be signifi-
cantly higher to enhance the inspections. The 1-m images depicted adequate de-
tail for features adjacent to the levee. The detection of very small anomalies
directly on the control structure, such as seepage or boils, was not reliable. This
disappointing conclusion suggests that high resolution satellite data would likely
not be a useful source of remotely sensed data for levee inspections. Even with
application of the pan-sharpening routine, IKONOS imagery reaches its highest
spatial resolution at 1 m. The QuickBird commercial satellite, operated by Digi-
talGlobe (Longmont, Colorado), offers a pan-sharpened multispectral product
with a 0.6-m spatial resolution. This slightly smaller pixel is beginning to ap-
proach the desired pixel size. Communications with the District has set the de-
sired spatial resolution at 0.25 m or higher (i.e., smaller than 25 cm).
The CAMIS system can easily provide 0.25 m imagery by decreasing flying
height during acquisition. However, the costs of post-processing and mosaicking
approximately 2560 frames would be prohibitive. Perhaps the best source of very
high resolution remotely sensed imagery would be a single-ccd digital aerial im-
aging system. These widely used digital cameras can produce cost-effective very
high resolution imagery with excellent geometric fidelity. The primary short-
coming of the single-ccd cameras is their limitation to only three spectral bands.
Thus, a decision must be made to choose either true-color or false-color images.
In addition, the output images are generally not suitable for advance processing
such as supervised classification. This is because of the techniques required to
generate three complete color planes from only one ccd array per image. Advan-
tages provided by these systems also include typically larger focal arrays, which
translate to much larger frames and fewer pictures needed to cover the area of
interest. Also, when equipped with a highly precise differential GPS (dGPS) re-
ceiver, used to generate very accurate aircraft positions (X, Y, and Z), along with
an inertial measurement unit (IMU), to record aircraft attitude parameters (pitch,
roll, and yaw), the frames can be rapidly post-processed to produce geometrically
accurate mosaics. Assuming that, for this levee inspection use, the images would
be used as enhanced background data in the ArcView application, there would
not be a need for a higher level of radiometric fidelity required for advanced im-
age processing techniques.
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