Inverse Synthetic Aperture Radar Imaging and Its Basic Concepts
Inverse synthetic aperture radar (ISAR) is a powerful signal processing technique for imaging moving targets in range-Doppler (or range and cross-range) domains. As range (or slant range) is defined as the axis parallel to the direction of propagation from radar toward the target, cross range is defined as the perpendicular axis to the range direction. An ISAR image has the ability to successfully display the dominant scattering regions (hot points), that is, scattering centers on the target. ISAR processing is normally used for the identification and classification of targets. The classic two-dimensional (2D) ISAR image is constructed by collecting the scattered field for different look angles and Doppler histories. Although ISAR processing is similar to synthetic aperture radar (SAR) processing, ISAR imaging procedure has some conceptual differences when compared to the SAR imagery.
4.1 SAR VERSUS ISAR
SAR generally refers to the case where the radar platform is moving while the target stays stationary (see Chapter 3, Figs. 3.1 and 3.3). The required spatial (or angular) diversity is accomplished by the movement of radar around the target or terrain. On the other hand, the term ISAR is used for scenarios when the radar is stationary and the targets are in motion, such as with airplanes, ships, and tanks, as illustrated in Figure 4.1. As similar to the SAR operation, the required range resolution is achieved ...