BROAD-BAND SYNTHETIC APERTURE SONAR

Most sonars, even chirped-pulse sonars, are narrow band in that their modulated bandwidth is a fraction of the carrier frequency. In this paper we look at the effects of a broad-band signal on the performance of a side-scan synthetic aperture sonar, including details on the necessary spatial sampling and resolution trade-offs. The mathematical description of the echo signals and the consequent image reconstruction algorithms are first shown for a step-and-go scenario that ignores the Doppler effect. Later, the extra modifications for the Doppler effect are introduced with some discussion of their probable impact. Simulated echoes and image reconstructions on hypothetical targets show the limiting performance and some of the effects of narrow-band reconstruction approximations on broad-band signals. For comparison purposes a few real images are presented taken from a CTFM 15-kHz-30-kHz sonar especially designed as a synthetic aperture sonar.