Synthetic aperture sonar

This letter describes the principle and the fundamental results of experiments of a synthetic aperture sonar which enables us to resolve objects both in angle and range more sharply than the conventional ultrasonic imaging system. The basic idea of this technique is to introduce pulsed waveforms to ultrasonic holography and its operations consist of collecting hologram signals with ultrasonic pulses and using a computer for storage of these signals and image calculation. The elementary experiments were carried out using a single‐wire target and ultrasonic waves of 1 MHz whose pulse duration was 12 μsec. The wire was set at a distance of 158 mm below the transducers and they were scanned over the hologram aperture of 50 mm across the wire. The results of the computer reconstruction were coincident with the theoretically expected values.