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33 Synthetic Aperture Radar Algorithms

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A synthetic aperture radar (SAR) is a radar sensor that provides azimuth resolution superior to that achievablewithits real beambysynthesizingalongapertureusingplatformmotion. | Clay Stewart. Synthetic Aperture Radar Algorithms. 2000 CRC Press LLC. http www.engnetbase.com . Synthetic Aperture Radar Algorithms Clay Stewart Science Applications International Corporation Vic Larson Science Applications International Corporation 33.1 Introduction 33.2 Image Formation Side-Looking Airborne Radar SLAR Unfocused Synthetic Aperture Radar Focused Synthetic Aperture Radar 33.3 SAR Image Enhancement 33.4 Automatic Object Detection and Classification in SAR Imagery References Further Reading and Open Research Issues 33.1 Introduction A synthetic aperture radar SAR is a radar sensor that provides azimuth resolution superior to that achievable with its real beam by synthesizinga long aperture using platform motion. The geometry for the production of the SAR image is shown in Fig. 33.1. The SAR is used to generate an electromagnetic map of the surface of the earth from an airborne or spaceborne platform. This electromagnetic map of the surface contains information that can be used to distinguish different types of objects that make up the surface. The sensor is called a synthetic aperture radar because a synthetic aperture is used to achieve the narrow beamwidth necessary to get a high cross-range resolution. In SAR imagery the two dimensions are range perpendicular to the sensor and cross-range parallel to the sensor . The range resolution is achieved using a high bandwidth pulsed waveform. The cross-range resolution is achieved by making use of the forward motion of the radar platform to synthesize a long aperture giving a narrow beamwidth and high cross-range resolution. The pulse returns collected along this synthetic aperture are coherently combined to create the high cross-range resolution image. A SAR sensor is advantageous compared to an optical sensor because it can operate day and night through clouds fog and rain as well as at very long ranges. At very low nominal operating frequencies less than 1 GHz the radar even penetrates foliage and can