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Table | Some civil Earth surface imagers 
instrument size, mass, and power consumption, and decreasing 
the GSD at the same time. In other words, what are the 
prospects for topographic mapping using small satellites in the 
next decade. 
2. TOPOGRAPHIC MAPPING CONCEPTS 
There are several possibilities to perform topographic mapping, 
most of them can make use of line or matrix technologies. 
1)  Across-track stereo (see fig. 3) due to side viewing feature 
(e. g. SPOT-1 - SPOT-4) 
2)  Along-track stereo 
2.1) 1 sensor concept using forward/backward slewing feature 
(see fig. 4) 
Phase | imaging in forward slewing mode 
Phase 2 imaging in backward slewing mode 
(e. g. IKONOS, EarlyBird (matrix camera), QuickBird) 
2.2) 2 sensor concept using forward/backward looking sensors 
with 
- 2 cameras, e. g. HRS on SPOT-5 
- 2 line arrays of a single camera, e. g. OPS on JERSI, 
ASTER on Terra (see fig. 5) 
3 sensor concept using forward/nadir/backward sensors 
with 
- 3 cameras, e. g. MOMS-02 on STS-55 and MIR/Priroda 
- 3 line arrays of a single camera, e. g. WAOSS-B on 
BIRD (see fig.6). 
N 
Lo 
ar 
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B1. Istanbul 2004 
   
  
   
   
    
    
  
   
  
  
     
    
    
  
  
  
100 
Landsat-1 
Resurs-O1-1 
* 
* 
* IRS-1A 
Landsat-4 
GSD Landsat-7 
[m] * 
10 n ADEOS $e 
SPOT-1 + EO-1 
$ SPOT-5 
EROS-A1 
* 
IKONOS-2 QuickBird-2 
1M MÀ € M4 
1970 1975 1980 1985 1990 1995 2000 2005 
Year of Launch 
Figure 2 Some civil Earth surface imagers, trend of GSD 
Orbit N Orbit N+1 
Across-track stereo 
e. g. SPOT-1 - SPOT-5 
Figure 3 Across-track stereo principle 
3. IMPORTANT PARAMETERS FOR MAPPING WITH 
SMALL SATELLITES 
IMPORTANT PARAMETERS FOR MAPPING WITH 
In this chapter only some major features are described and a few 
suggestions are given to support miniaturization in order to 
come in the range for small satellite designs. 
3.1 Spatial resolution aspects 
Some major features are considered which influence the image 
quality from the spatial resolution point of view. A very 
effective way to describe the image quality is to use the 
Modulation Transfer Function MTF. It can be cascaded in order 
to combine all the different influence elements 
MTF, = MTF, . - MTF,, - MTF, - MTF, (1) 
Optics 
(SR — spatial resolution, LM — linear motion, J — jitter or 
random motion, D — detector) 
MTF pics includes the diffraction part as well as the aberration 
part.