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x-or flight- direction y- or line- direction 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Fig. 9 PSE/MTF measurements along the nadir-line in in steps of 4 degree 
For modern image processing and image restoration methods the knowledge of PSF or MTF at every image forming point is 
necessary and therefore the PSF has to be measured in the calibration period of the camera. The PSF is measured at the same 
pixels which were used for the angle determination. The PSF is in reality a two-dimensional function depending of x ànd y 
coordinates. With the camera calibration facility the PSF is sampled in the two main directions one in line- or y-direction and 
the other perpendicular to the first in in swath- or x-direction. The same pixels which were selected for the geometric 
calibration also were used for PSF-measurements. As the result we know the PSF at 21 equidistant points of each line in the 
two main directions and the PSF between this points can be estimated. The measured PSF's and MTF's along the nadir line 
of the WAOSS camera are shown in fig. 9.. It is mentioned here that it is the PSF for the whole camera system as 
convolution of the optical PSF, the PSF of the 7um pixel size and the PSF-forming processes of the CCD-mechanism and 
read-out electronics. 
The modulus of the Fourier-transformed PSF is the well known MTF which shows the transfer behaviour in the frequency 
domain. 
IAPRS, Vol. 30, Part 5W1, ISPRS Intercommission Workshop “From Pixels to Sequences”, Zurich, March 22-24 1995