DESIGN AND CALIBRATION OF A MULTISPECTRAL AIRBORNE DIGITAL IMAGING SYSTEM (MADIS)

The requirement for radiometrically calibrated imagery in research and consultancy activities have necessitated the design and construction of an "affordable " multispectral imaging system using off-the-shelf camera and computer-support hardware. This paper describes the design, construction and preliminary calibration of a Multispectral Digital Imaging System (MADIS) comprising four progressive-scan, 1k x 1k, digital cameras. The cameras, with respective optical filters, are multiplexed in pairs onto two digital camera interfaces. The progressive scan architecture eliminates image shear resulting from interlaced fields produced by conventional video cameras often employed in low-cost multispectral imaging systems. The camera frame-store capability allows sequential read-off of the simultaneously triggered camera images, providing temporally registered, 4-band composite imagery. Image brightness is controlled using electronic shuttering and fixed apertures to avoid radiometric calibration errors associated with the use of continuously variable aperture controllers. The use of 12.5 mm focal-length lenses on each camera provides 1 m resolution imagery (approximately 1 km x 1 km footprint) at an operating altitude of 1422m. The system has been designed to fit in the floor of a Cessna 310 aircraft, and only minor modifications are required for mounting it in the passenger doorway of a high-wing single-engine aircraft. Operational, calibration and design characteristics of this new system are compared with those of an older-generation analogue multi-camera video array