Talk:E-8 Joint STARS

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 Definition A radar aircraft optimized for surveillance of a large land or sea area, returning both tracks and identification of moving vehicles, or radar imaging of the surface. [d] [e]

SAR

If anyone is willing to help on revising the SAR discussion in the Radar MASINT article, and/or breaking out separate SAR/ISAR articles, I'd greatly appreciate it. There's a very delicate line between MASINT and IMINT when it comes to SAR/ISAR, especially getting into things like MTI, and it's not one of my areas of specialization. Howard C. Berkowitz 01:02, 18 May 2008 (CDT)

Two things. First, I had a look at the Radar MASINT article, and it's quite lengthy, so that the material there on how SAR works could profitably be moved to a SAR article, to shorten the MASINT one.
Second, the description there seems to have missed what I see as the fundamental concept of SAR (as I understood it, maybe I'm wrong), which is to combine data from many 'separate' omnidirectional antennas (which may be actual physical antenna array elements, or, in the usual airplane case, it takes advantage of the motion of the airplane to move one antenna through a range of locations), to provide higher resolution than a single antenna could. That's the 'synthetic aperture' part, using the standard terminology for a key factor in the resolving power of a telescope, its size (aperture): the information from many smaller detectors is combined together to simulate (synthesize) a larger one. The moving aircraft simulates multiple antennas spatially separated over a distance much larger than the size of the antenna, or the airplane, itself. Similar techniques are used in a variety of areas, such as Very Long Baseline Inferometry, by radio astronomers, although the exact techiques, which use very complex math to add together correlated information received at the different 'antennas' (I think VLBI techniques are now being used with light too), differ in the details. The basic technique uses only the amplitude of signal returns, but one can also (with enough processing power) gain useful information from the phase and polarization of the returned signal. Finally, the airplane application, because of the motion of the transmitting antenna, allows one more kind of information contained in the return signal to be mined, which is frequency; returns from different directions (relative to the motion of the aircraft) will be Doppler-shifted to different frequencies, so with high-accuracy control of the frequency of the transmitted pulse, the direction of returns can be very accurately determined. Phased-array radars use a similar basic concept (adding together many smaller omnidirectional antennas) but they apply it to the outgoing signal, creating a 'steerable' beam. J. Noel Chiappa 08:16, 18 May 2008 (CDT)