Hans Peter Röser 
  
3 ADS CAMERA CHARACTERISTICS 
LH Systems, like its predecessor Leica, is an expert in the development and worldwide use of film aerial cameras 
(www.Ihs). In view of the new digital technologies, the company decided a few years ago to develop an airborne digital 
sensor jointly with the German Aerospace Center (DLR) in Berlin, which has research activities and a long tradition in 
the development of digital cameras including stereo and multispectral capability for different space missions (Albertz96, 
Sandau96, www.dlr). The development has been completed, test flights have been done, first with an engineering and 
later on with a prototype model, and the production version is scheduled for the market in mid-2000. 
The first step in the development was the decision to use the three line scanner approach instead of CCD matrix arrays, 
The reasons for that are manifold: larger swath width, multispectral performance with well-defined wavelength bands 
for each CCD line, and cost. But using a line scanner has also a disadvantage given by the fact that aircraft tilts cause 
the linear arrays to image widely varying strips of terrain which has to be corrected as shown in Figure 4. 
The ADS camera has eight parallel sensor lines, three panchromatic lines (forward, nadir, backward), three lines used as 
Red, Green and Blue channels and two different NIR channels. They are all placed on one focal plane of a single lens 
system with a focal length of 62.5 mm. The panchromatic lines with different angles (Sandau2000) provide the stereo 
capability. Each panchromatic line consists of two linear arrays, each with 12000 pixels but staggered by a 0.5 pixel 
shift. The color sensor lines RGB, also with 12000 pixels, are optically superimposed during the flight. This is 
accomplished with dichroitic mirrors, which divide the incoming light beam into three color components followed by a 
narrow filter band. 
  
—— Eli Pitch — VAN 
  
Figure 4: Imagery over Berlin with a 3 line scanner 
The well-defined separation of the different wavelength bands is important to make ADS, combined with an appropriate 
post processing, a powerful tool for remote sensing. The lines of the NIR channels — one of them is optional - have 
12000 pixels each and are slightly offset to the RGB triplet. The dynamic range of the CCD is 12 bit with a radiometric 
resolution of 8 bit. This is very much higher than the best film material available. The read out frequency of each line 
can be adapted to the flight velocity and altitude of the aircraft in the range from 200 to 800 Hz. The selection of the 
spectral channels is a compromise, taking into account the most frequent tasks which have to be fulfilled depending on 
the surface reflectance and minimizing the atmospheric distortion. A focal length of 62.5 mm in combination with a 
staggered 2 x 12000 pixel CCD array results in a field of view across the track of 64 degrees. Assuming a flight altitude 
  
254 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part Bl. Amsterdam 2000. 
  
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