Underwater Parametric Reception in the Case of a Spherically Spreading Pump and a Plane-Wave Signal

Parametric reception is an economical means of generating a large virtual continuous end-fire array to gain directivity in the detection of low-frequency signals. In this paper, we assume a spherically radiating pump that mixes with a plane-wave low-frequency signal to generate a secondary sound field at the sum and the difference frequencies. A closed-form solution for the radiated secondary sound field is presented and compared with an “exact” numerical solution. Both theoretical methods are shown to be in good agreement with one another and an experiment performed in a fresh water lake. The experiment consisted of a pump mounted on one end of a 50-ft 1 beam projecting a 90-kHz narrow beam to a receiving hydrophone on the opposite end of the 1 beam. The signal was a 5-kHz fixed source located 150 ft from the center of the 1 beam. The receiving system was tuned to (90±5) kHz and as the 1 beam was rotated, beam patterns were generated that agree well with the theoretical results. [This work was sponsored by the Office of Naval Research.]