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5. MTF CONSIDERATIONS 
The geometrical resolution of the camera system 
essentially depends on the MTF of the system 
optics/CCD pixel. It describes the damping of the 
incoming radiation as a function of the spatial 
frequency. This may serve as a basis to define a 
contrast function. 
Considering only this optics/CCD-pixel system, the 
MTFsys is calculated by multiplying the MTFs of 
the system constituents MTFoptics and MTF PIX el 
MTFsys — MTFoptics MTFpixel (5) 
The MTFpixel of the CCD pixel is: 
sin (n-k-x) 
MTFpixel = (6) 
{K - k-x) 
with k being the spatial frequency measurement in 
mm and A being the pixel distance, here 6.5 pm. 
The function MTF PIX ELis shown in Figure 9. 
MTF 
Fig. 9. MTF of CCD pixel, distance of pixel centers 
6.5 pin. 
MTF 
laboratory of the DLR Institute for Space Sensor 
Technology in Berlin, Adlershof. The second curve 
in Figure 10 is the resulting MTFsys for the nadir 
looking pixel. 
To allow for comparison with the MTF of the pixel 
given in Figure 9, a wider range of MTFsys is 
shown in Figure 11. 
MTF [%] 
Fig. 11. MTF of a pixel near the optical axis of the 
engineering model 
With a MTFsys of -30% at the Nyquist frequency: 
given for A = 6.5 pm, a number of k NY = 77 Lp/mm 
(Line pairs per mm), the contrast potential and 
therefore the imaging quality of the EM is pretty 
good. This holds also for the non-nadir areas of the 
focal plane used by the nadir and stereo looking 
CCD lines, since the MTFsys does not deviate 
dramatically form the shown curve. Figure 12 gives 
a measured curve for the centre of the stereo 
forward line (17° stereo angle) in comparison with 
the centre of the nadir line. 
MTF I % I 
Fig. 10. MTFoptics of MTFsys of the engineering 
model (EM) at the optical axis. Fig. 12. MTF of centre of nadir line (0°) and centre 
This Figure shows the MTFoptics of the EM optics °f forward stereo line ( at 17° stereo angle) 
measured in the optical axis of the calibration