High Spatial Resolution Digital Imagery
5
2
IMAGE ACQUISITION
2.1
CAMIS
A flight mission is needed to acquire high-resolution imagery using the
CAMIS model 4768P, developed by Flight Landata (Lawrence, Massachusetts)
(Fig. 1). Unlike other currently available airborne digital camera systems, which
employ a single CCD technology, the CAMIS optical head consists of four Sony
XC8500 progressive scan cameras mounted on a sited solid base. Each camera is
sensitive in the range of 3501100 nm. Bandpass interference filters determine
the wavelength interval recorded by each camera. The standard wavelength con-
figuration was used for this mission--25 nm bandpass filters centered at 450 nm
(blue), 550 nm (green), 650 nm (red), and 800 nm (near infrared). The CCD di-
mensions in each camera are 768 576 square pixels with 8-bit radiometric
resolution. An aircraft altitude of 6115 ft (1865 m) above ground level (agl) pro-
duces a nominal spatial resolution of 1 m per pixel.
The CAMIS processing unit consists of a 233-MHz Pentium processor with
64 MB of RAM, 23-GB hard drive, and a Matrox Genesis Image Processing
Card with 24-MB onboard memory. A Motorola Oncore GT global positioning
system (GPS) receiver obtains absolute code phase positions for the center pixel
of each image. The system was mounted and flown onboard a Cessna 172 Sky-
hawk. The pilot navigated to each site and along each flightline using an onboard
moving map with code phase GPS.
Geographic coordinates defining the extent of each individual reference are
needed to develop a series of flightlines that encompassed the extent of each set
of coordinates. As the CAMIS system acquires images as discrete four-band
digital frames, flightline calculations are identical to those used for standard ae-
rial photographic missions. Nominal frame-to-frame overlap (or endlap) should
be 60%, while nominal flightline sidelap should be at 20%. Data capture occur-
ring within 1.5 hours of solar noon ensures optimal solar illumination and to
minimize shadows.
2.1.1 Poplar Island Restoration
CAMIS images were acquired on 11 February 2001 between 1100 and 1200
hours. Conditions were sunny with light winds, providing adequate solar illumi-
nation and acceptable aircraft attitude during image acquisition. Ten unique ref-
erence wetland sites were covered. Figure 2 depicts the completed flightlines
over several sites on or near Tilghman Island, Maryland. The orientations of the
Previous Page
