Digital photogrammetric cameras: possibilities and problems

Airborne digital sensors are about to widen the choices in photogrammetry. The transition from analytical to digital photogrammetry is well advanced and the dividing lines between photogrammetry and remote sensing grow increasingly blurred. One of the advantages of direct digital data capture in the air is the possibility of capturing multispectral data as well as panchromatic. Positioned between modern film-based aerial mapping cameras with their extremely high resolution and, at the other end of the spectrum, the forthcoming high-resolution satellite sensors, the new airborne devices can access a large market. Two technologies are available as the basis for airborne digital sensors – linear and area array CCDs. The performance of the latter is insufficient to offer swath widths and resolutions comparable to film cameras. The most promising alternative appears to be linear arrays, arranged in a triplet on the focal plane, one forward-, one nadirand one backward-looking. When combined with GPS and INS systems, this configuration provides geometric performance that enables the same photogrammetric operations to be performed on the workstation as with scanned film imagery. Radiometric issues such as the signal to noise ratio must be fully taken into account. Moreover, multispectral CCD lines can also be placed on the focal plane, providing data tractable by image processing techniques from remote sensing, with the additional advantages of geometrically correct sensor modeling, stereo imagery and accurate geocoding. A development project between LH Systems and the German Aerospace Centre has resulted in a functioning three-line sensor. An engineering model has flown successfully and a production model is scheduled for market introduction in summer 2000.