The Application of Holographic Concepts to Sonar

Abstract

The conventional signal processing and beam-forming tasks that must be performed in a sonar system are traditionally accomplished by electronic analog and digital means. Conceptually, these signal-processing tasks can be very conveniently accomplished with optical systems, although the required accompanying optical input recording process is usually a practical difficulty. From another point of view, the process of acoustical holography, with optical reconstruction, can be used as a sonar device, i.e., to see objects in water. These two conceptual approaches to sonar have much in common, and are both subject to several fundamental limitations. An important difference between them is the pulse echo-timing ability of conventional sonar, where range information is implied by echo delay, versus the CW nature of a holographic system, where range is obtained by parallactic or focusing effects. Hybrid systems are possible which incorporate the attributes of both approaches.