Imaging using synthetic aperture techniques is a mature under the guise of Project Wolverine to develop a high-resolution technique with a host of different reconstruction algorithms available. combat-surveillance radar system [4]. The ability of SAR to Often the same basic algorithm has a different name depending on remotely observe a scene through cloud cover during day and where the particular algorithm is used, since it may have originated night and through light rain made it ideal for use as a tactical from the medical, nondestructive testing, geological, or remote sensweapon. The development of the early work in synthetic aperture ing fields. All this adds to confusion for the nonspecialist. This article radar (or SAR, at it is more usually known) is retraced by Shergives a short historical precise of active synthetic aperture imaging win et al. in [1]; a review of his personal involvement is made as it applies to airborne, spaceborne, and underwater remote sensing by Wiley in [2]. Curlander and McDonough [3] also retraced systems using either radar or sonar, then defines some generic imdevelopments from an insider's point of view. aging geometry and places all the usable synthetic aperture reconstruction algorithms in a unified framework. This is done by the intro-Early workers considered unfocused SAR [5]; however, at duction of mapping operators, which simplify the mapping or rethe 1953 meeting, Sherwin indicated that a fully focused synthetic formatting of data from one sampling grid to another. Using these aperture (SA) would produce finer resolution [6, p. 339]. In operators, readers can see how strip-map synthetic aperture systems 1961, Cutrona et al. first published the fact that a fully focused (both radar-and sonar-based) differ from spotlight synthetic aperture synthetic aperture produces an along-track resolution that is indesystems, how the various algorithms fit together, and how the chirppendent of range and wavelength and depends only on the physiscaling algorithm is likely to be the reconstruction algorithm of choice cal size of the illuminating antenna [1,7]. The major problem for most future strip-map systems, and just why that should be so.
faced by the initial developers of a focused SAR processor was Multilook processing and methods to deal with undersampled apertures using postdetection digital spotlighting are put into the same the range variance of the along-track focusing filters. This probunified framework, as both of these techniques are frequent adjuncts lem was overcome with the development of the first optical procto synthetic aperture imaging.