Frank Gerlach 
  
  
  
  
The end to end system requirement for MTF is 0.10 measured at the Nyquist frequency of 41.6 cy/mm for the 3.1 
pan system. This includes a display multiplier of 0.91. Therefore, one would expect a system MTF exclusive of 
display of 0.11. This is for a target contrast ratio at the entrance aperture of 2 to 1, with 24 TDI. . The MTF's for The 
the multispectral system are 0.17, 0.19, 0.21, and 0.23. Figure 5 shows the deployed edge target. The ground entr 
measured contrast ratio is about 6.5 to 1. The contrast ratios measured at the focal plane from six images 14.( 
collected on four different dates varied from 3.6 to 5.7 ave 
fiel 
Figure 6 shows the on orbit measured MTF for the pan system, where a relative spatial frequency of 0.5 all f 
represents the Nyquist frequency of 41.7 cy / mm. The flat field MTF, i.e., calculated at zero spatial frequency, is witl 
89 to 1 for the pan band. The MTF's for the MS bands 1 through 4 are: 0.26, 0.28, 0.29, and 0.27 respectively. 
32 
The 
boa: 
Wat 
pro 
TDI 
time 
ther 
usin 
rela 
of a 
the | 
MS 
0 0.1 02 03 0.4 05 
Frequency 
Figure 5 Edge target Figure 6 On orbit measured system MTF (exclusive of display) 
In addition, imagery products can be ordered with transfer function compensation, MTFC, either on or off. MTFC applies 
the inverse of the known system induced point spread function, governed by the laws of physics, to remove the blurring 
introduced primarily by the optics and detector. Even with a perfect camera system, some blurring is induced. IKONOS is 
a diffraction limited, Shot noise limited system with a sampling ratio of approximately two pixels per Airy disk. Figure? 
shows a comparison of the same image both with (right image) and without MTFC. It is suggested that imagery be 
ordered with MTFC on, even for multispectral products, the rationale being that the energy is being placed back into the 
pixels that it should have originated from. 
31 
The 
use ( 
3.1.1 
Figure 7 IKONOS one meter image without and with MTFC 
  
132 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B1. Amsterdam 2000.