Acoustic imaging and holography

Applications of active and passive devices employing the characteristics of sound to obtain results have been known to investigators for many years. However, in addition to these sonar or pulse-echo methods of analysis, there exist a variety of techniques in which a sound image is obtained in a way more analogous to optics. This analogy has, in the last few years, been extended to include holographic techniques, and has led to the inception of a new discipline-acoustic holography. In this article, we trace the development of this new field as it originated from a fusion between ``conventional'' acoustic imaging and optical holography; and we see how, in the few years of its existence, it has already generated its own unique methods and problems.