An experiment involving the design and construction of a prototype sub-bottom high resolution sonar system utilizing nonlinear pulse self- demodulation and suitable for deep water use is described. It is possible to generate a low frequency wave using the self-demodulation of a short, high frequency, finite amplitude pulse produced by the non-linear properties of the medium. The generated low frequency wave will theoretically have the high directivity of the primary wave while simultaneously possessing the bottom penetrating characteristics of the lower frequency. Measurements demonstrate that the pulse self-demodulation occurs as theoretically predicted, and the results are successfully applied to the design of the sonar system. Shallow water tests demonstrating the potential effectiveness of the sonar system for detection and classification of target objects in bottom sediments are also described.

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http://archive.org/details/subbottomhighres1094520359

Lieutenant, United States Navy