while forward scanning is provided by the along track mo- 
tion of the platform. Infrared scanners can produce an ima- 
ge that rivals the olarity of a film camera. Scanners are 
used where one needs a large total field of view añd high 
resolution but the platform cannot carry a large collector. 
Scanners are disadvantaged by mechanically moving parts. 
Nevertheless, this effect can be eliminated by proper cali- 
bration, a better solution is the application of "image dis- 
sector” tubes. Dissecting the image provides a wide range 
of operational modes, flexibilities not available in other 
types of scanning systems, and the possibility to elimina- 
te all mechanically moving parts of the scanner. 
3.4 SPECTOMBTERS 
The application of spectrometers in remote sensing is 
based on the principles of spectroscopy. Their basic pro- 
perties, which are of concern in remote sensing are: resol- 
ving power, i.e., the ability to separate one wavelength 
of light from another, and the ability to collect and use 
light. These two properties are indirectly proportional. 
There are two ways in which the efficiency of spectrome- 
ters can be improved: /1/ multiplexing, that is observing 
the light in more than one.wavelength at the same time,and 
/2/ to increase the total amount of light that the instru- 
ment can collect. 
3.5. RADARS 
Radar is a radiometer that supplies its own scene il- 
lumination and operates in the microwave portion of the 
electromagnetic spectrum, In general, radar has all-weat- 
her, day and night capabilities. The main disadvantages 
are: the relatively poor resolution, the required long an- 
tennae /difficulties of their stabilization/, and the pro- 
blems of energy supply. 
Various methods may be used to improve the resolu- 
tion of conventional radar. Range resolution can be impro- 
ved by processed short pulse length technique, while along- 
track resolution using the method of synthetic-aperture 
/synthetic antenna/. 
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