International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
  
  
  
  
  
  
   
    
    
   
    
     
  
   
    
   
  
  
   
    
   
   
    
     
   
  
  
   
   
  
  
    
    
  
  
   
   
   
Figure 4 
Figure 5 
Figure 6 
Along-track stereo 
1 camera (matrix or line) 
Forward/backward slewing feature 
matrix: e. g. EarlyBird 
line: e. g. IKONOS, QuickBird 
  
Along-track stereo using the slewing feature 
of the satellite or platform 
  
Along-track stereo 
2 lines on 1 FPA / camera 
2 single line cameras 
or 
1 camera: e. g. OPS of JERS-1 
2 cameras: e. g. HRS of SPOT-5 
- — V 
Along-track stereo 
3 lines on 1 FPA (e. g. WAOSS) or 
3 single line cameras (e. g. MOMS-02) 
Along-track stereo with 2 sensors 
  
Along-track stereo with 3 sensors 
For most of the operating systems, the optical system may be 
considered near diffraction limited and in focus. The Airy disk 
diameter d caused by diffraction is one of the important 
parameters which can be related to the detector pixel size x 
d-244.A 244. A-F (2) 
with f the focal length, D the aperture of the optics, and À the 
average wavelength of the radiation. If x is larger than d the 
system is detector limited, the resolution is determined by the 
detector. Otherwise the optics determines the spatial resolution. 
Figure 7 shows the borderline for an average wavelength of 
A =0.55um (green). The optics designs should be near to the 
borderline on the optics limited side in order to get maximum 
energy for the detector avoiding too large aliasing effects. F 
state-of-the-art CCD detectors with a pitch of 7 um, a f/5.2 
optics would satisfy this approach. 
The MTF degradation due to linear motion of the satellite is 
MTF M (1) ES inc(a,,, 1 £3 (3) 
where f, is the spatial frequency, and aj, the distance the target 
edge moves across the detector pixel. MTF,m only effects the 
MTF in the direction of the motion. The distance a, y is V: A. 
In many cases At is close to the dwell time and MTF, is 
approximately MTFp. As a rule-of-the-thumb, when the linear 
motion causes an image shift less than about 20 % of the 
detector size, the effect on system performance is minimal. 
For MTF; (jitter or random motion) is assumed that the jitter is 
a superposition of different high-frequency motions so that the 
central limit theorem can be applied. It says that many random 
movements can be described by a Gaussian distribution 
MTF(f,) 2 exp( -2z7^0; f?) (4) 
with o; the rms random displacement. As a rule-of-the-thumb, 
when ©; is less than about 10 % of the detector size x, system 
performance is only minimal effected. Attitude control systems 
for pointing accuracies and stabilization to support high 
resolution functions on micro satellites are under development. 
In some cases, disturbing vibrations may also be avoided by 
simply switching off the active control functions during the 
relatively short imaging phase. 
3.2 Radiometric aspects 
The number of photoelectrons generated in a solid state camera 
is 
Aj : Topics : Fe z = 
Hn x i ES (A) L(A)dA (5) 
   
  
Internatic 
(Ap == de 
integratio 
radiation 
Once the 
given as 
designed 
constraint 
variable | 
the satell 
words, th 
of 7m. F 
< 1/7 ms 
Lavell ( In 
Even mo 
(IFOV ). 
IFOV( 
Taking bc 
of 10”! c: 
energy at 
There are 
= Use | 
signal 
(this t 
missi 
- use tf 
groun 
with resp 
necessary 
Airy disk d [micrometer] 
Figure 7 
3.3 Mas 
S3 À 
1972... 4 
sophistice 
MESUR I