Back in the 1990s, when experimentation began on developing digital aerial cameras, the basic design problems involved getting enough pixels into the focal plane to capture an adequate level of detail qua ground coverage, and how to acquire colour images. The basic solutions were either to place linear CCD arrays in the focal plane or to use several, area CCD chips. In the linear-array architecture one single lens head can be used, while colour (or multi-spectral-band capture) is obtained by placing three (or more) linear arrays in the focal plane, upon each of which are projected different parts of the visible electronic-magnetic spectrum; enabled by beam-splitters. The area-CCD-array solution is a camera consisting of several cones (multi-head). For example, the sensor head of Vexcel's UltraCamX consists of eight independent camera cones, four of which contribute to the large-format panchromatic image and four to the multi-spectral image: blue, green, red and infrared.

Applanix entered the digital aerial camera market as a provider of integrated GPS/INS systems which, mounted in the aircraft, made it possible directly to determine the six parameters of exterior orientation. The logical step now was complete integration of an imaging sensor into such a system. In addition to the here listed DSS 422, in May 2007 Applanix introduced the DSS 439. This camera differs from the DSS 422 only in a few sensor characteristics. Sensor format is 49.0mm x 36.0mm; effective pixels per CCD is 39MP, pixel size is 0.0068 micrometre; number of pixels across track is 7,216 and along track 5,412. In addition to the DIMAC 2.0, since last year DIMAC Systems has also manufactured the DIMAC light, which differs slightly from DIMAC 2.0; there are one to two lenses and the number of across-track pixels is 7,216 and along-track 5,412. Wehrli's here listed 3-OC-1 system represents a slight modification of the 3-DAS-1 and is specially designed for capturing oblique images, while the 3-DAS-1 is designed for taking vertical images. Wehrli's camera architecture is based on linear-array CCD technology.

The term GSD means Ground Sample Distance, or pixel size on ground. More information on types of camera architecture adopted by the various manufacturers can be found here.

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