We now turn our discussion to a particular type of SAR system known as spotlight synthetic aperture radar. This SAR imaging modality utilizes mechanical or electronic beam steering of a physical radar. The purpose of the beam steering is to irradiate a finite target area centered around the point (Xc, Yc) in the spatial domain as the radar is moved along a straight line. The mechanical or electronic beam steering, which maintains or focuses the physical radar radiation pattern on the same target area while the radar-carrying aircraft moves along the synthetic aperture, is called analog spotlighting.

Spotlight SAR is more “modem” than stripmap SAR, which is discussed in Chapter 6. However, the reader should not be misled by the word modern in assuming that spotlight SAR is preferable to stripmap SAR. Spotlight SAR and stripmap SAR are two different SAR imaging modalities. In fact, in SAR reconnaissance problems, the user might first run a stripmap SAR data collection to obtain an image of a relatively large target area, for example, a battlefield. Then, by analyzing this image and identifying smaller target areas that appear to be of interest, a spotlight SAR data collection for each of the smaller target areas is run to obtain high-resolution imaging information. (See also the introductory discussion on stripmap SAR in Chapter 6.)

Beyond the application differences of the two SAR systems, the classical range-Doppler imaging, which ...

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