Sonar and calibration utilizing non-linear acoustic reradiation

An apparatus for determining parameters in an aqueous environment comprising:

• an acoustic projector positioned in said aqueous environment for projecting an acoustic beam having at least one preset frequency;
• a non-linear acoustic reradiator positioned in said aqueous environment to receive said acoustic beam and reradiate an acoustic wave having a different frequency than said preset frequency said non-linear acoustic reradiator comprising a transducer positioned in communication with said aqueous environment, a series resonant circuit electrically connected to said transducer, and a non-linear element electrically connected in series with said series resonant circuit and said hydrophone;
• a hydrophone positioned in said aqueous environment to receive said reradiated acoustic wave;
• and
• detection means in communication with said hydrophone for detecting parameters of said reradiated acoustic wave received by said hydrophone.

A method for calibrating a hydrophone in a aqueous environment comprising the steps of:

• providing a non-linear acoustic reradiator having known reradiation characteristics;
• directing an acoustic beam having a preset frequency towards said provided non-linear acoustic reradiator;
• receiving said directed acoustic beam at said provided non linear acoustic reradiator;
• changing the preset frequency of said acoustic beam at said provided non-linear acoustic reradiator to a different frequency, said different frequency and amplitude values being known;
• reradiating different frequency acoustic waves from said provided non-linear acoustic reradiator;
• receiving said reradiated acoustic waves at a hydrophone;
• detecting the frequency and amplitude of said reradiated acoustic waves;
• comparing the frequency and amplitude of said received reradiated acoustic waves with known frequency and amplitude values for said different frequency acoustic waves reradiated from said provided non-linear acoustic reradiator;
• and
• determining hydrophone characteristics based upon said step of comparing.