System Requirements for Underwater Acoustic Holographic Mapping

The relations among the holographic parameters of focal length, aperture, and wavelength and the system parameters of resolution and stability in the horizontal and vertical are developed for the application of acoustic holography to mapping and searching the sea floor. The relative advantages of pulsed and continuous acoustic sources are discussed, the concept of the sanitized signals from a pulsed source is introduced, and the implications in terms of forbidden zones and statistical uncertainty in the amplitude of the mean scattered signal are developed. The information content of the acoustic holographic surface and the required sampling spatial density are presented. The area scan rate of the holographic system is related to the system parameters. A conceptual design of an acoustic deep-water holographic system, Sea Fan, is described as an example of the application of the constraints previously developed. The scan rate of Sea Fan is compared with some present methods of searching the sea floor. An optical reconstruction process involving the superposition of a cohologram and a quadrature hologram is described.