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Fundamentals of Remote Sensing

3.3 Answer

The high altitudes of spaceborne platforms (i.e. hundreds of kilometres) preclude the use of real aperture radar (RAR) because the azimuth resolution, which is a function of the range distance, would be too coarse to be useful. In a spaceborne RAR, the only way to achieve fine resolution would be to have a very, very narrow beam which would require an extremely long physical antenna. However, an antenna of several kilometres in length is physically impossible to build, let alone fly on a spacecraft. Therefore, we need to use synthetic aperture radar to synthesize a long antenna to achieve fine azimuth resolution.
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