Method for detecting acoustic signals from an underwater source

• US 5,668,778 A
• Filed: 07/09/1996
• Issued: 09/16/1997
• Est. Priority Date: 07/09/1996
• Status: Expired due to Fees

• Current Assignee: Navy Department United States of America The As Represented By The Secretary of The Navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Quazi, Azizul H.
• Primary Examiner(s): Pihulic, Daniel T.
• Application Number:
  US08/677,205
• Time in Patent Office: 434 Days
• Field of Search: 367/135, 367/136, 367/124, 367/98, 367/87, 367/131, 395/2.09, 364/423
• US Class Current: 367/135
• CPC Class Codes: H04B 11/00 Transmission systems employing sonic, ultrasonic or infrasonic waves

Abstract

A method for detecting radiated and reflected acoustic signals from an unwater source, wherein the acoustic signals are present in a random noise environment and form an output therewith. The method includes the steps of operating an entropy-based acoustic receiver to receive the output, calculating the entropy of the received output, and comparing the calculated entropy with a selected entropy threshold value. A substantial difference is indicative of the presence of an acoustic signal from an underwater source. A less than substantial difference is indicative of a lack of presence of an acoustic signal from an underwater source.

Claims

1. A method for detecting radiated and reflected acoustic signals from an underwater source, wherein the acoustic signals are present in a random noise environment and form an output therewith, the method comprising the steps of:

operating an entropy-based acoustic receiver to receive said output;

calculating the entropy of said output;

comparing the calculated entropy with a selected entropy threshold value;

wherein a substantial difference revealed by the comparison of the calculated entropy and the selected entropy threshold value is indicative of the presence of an acoustic signal from an underwater source; and

wherein a less than substantial difference revealed by the comparison of the calculated entropy and the selected entropy threshold value is indicative of lack of presence of an acoustic signal from an underwater source.

2. The method in accordance with claim 1 wherein in order to calculate the entropy of said output, the entropy is estimated as to amplitude in bits on a window of digital points.

3. The method in accordance with claim 2 wherein said window is a sliding window with an overlap.

4. The method in accordance with claim 2 including the step of plotting said estimated entropy as a function of window number.

5. The method in accordance with claim 4 including the step of applying a threshold in bits to the plot derived from plotting said estimated entropy, to reveal the presence of non-stationary signals evidenced below said threshold.