Aerial photography was acquired using a frame based digital camera
(UltraCamD (UCD), UltraCamX (UCX), or DMC), therefore no scanning conversion
from film to digital was needed. Geometric and radiometric
calibration for each one of the camera heads is determined in the
manufacturing laboratory. This step is also known as geometric and
radiometric calibration of a single camera head and done when the
sensor is being manufactured. The 4 multispectral heads collect
4 separated bands: Red, Green, Blue and Near Infrared wavelength.
Both the UltraCam and DMC sensors collect 12bit data. The UCD sensor
CCD pixel size is 9 micron with a footprint of 7500 pixels in the
long track, and 11500 pixels in the cross track.
The UCX sensor CCD pixel size is 7.2 micron with a footprint of
9420 pixels in the long track, and 14430 pixels in the cross track.
The DMC sensor CCD pixel size is 12 micron with a footprint of
7680 pixels in the long track, and 13824 pixels in the cross track.
Twin Engine Navajo, Turbo Commander and Conquest aircrafts
were used, flying at average flight height of 6,700 to 8,600 meters above
ground, allowing image acquisition of 0.67 to 0.86 meters Ground Sample
Distance. An INS - Inertial Navigation System, with
AGPS (Airborne GPS) and IMU (Inertial Measurement Unit) was utilized for
all aerial missions. The INS allows for accurate photo-center
registration and image orientation. For inspection and verification of
accuracy of the exterior orientation computed with the Inertial Navigation
System, stereo compilation was performed for every flight mission and its
result compared against higher accuracy source data. If a test of
positional accuracy failed (> 5 meters) a full analytical triangulation
is processed for that mission, assuring accurate horizontal positioning.
USGS seamless NED data was used as a surface for ortho-rectification.
Sanborn used proprietary software called METRO to rectify the scanned images.
Rectification was done using cubic convolution resampling. Color balancing
was then performed on each exposure. Sanborns software tonally balanced
each exposure to alleviate the effects of hotspots, side-to-side shading
within an exposure, and tonal differences between flightlines due to
dissimilar conditions at the time of capture. Each exposure was then
balanced to predefined target values used throughout the project,
creating a dataset consistent and uniform in radiometry. Seams between
exposures were determined by Sanborns software to use the best exposure
based on proximity to nadir and ground angle to the camera. Delivery
tiles were then extracted from Sanborns seamlessimagery database, named
to meet the DOQQ and/or DOQ naming convention, and formatted as defined
in the task order. Horizontal accuracy was once again tested for 6-meter
absolute accuracy. If failed, then the entire flight mission would be
revised, a new aerotriangulation performed and new set of doqqs produced.
Quality control was performed on a sampling of each deliverable to ensure
no artifacts or anomalies were present in the imagery.