Method for locating an underground septic tank, conduit, or the like using injection/detection synchronization of an acoustic signal and digital signal processing

• US 8,116,994 B2
• Filed: 11/23/2008
• Issued: 02/14/2012
• Est. Priority Date: 11/23/2008
• Status: Active Grant

• Current Assignee: David H. Parker
• Original Assignee: David H. Parker
• Inventors: Parker, David H.
• Primary Examiner(s): Nghiem, Michael
• Application Number:
  US12/276,350
• Publication Number:
  US 20090112476A1
• Time in Patent Office: 1,178 Days
• Field of Search: 702/6, 702/56, 702/159
• US Class Current: 702/56
• CPC Class Codes: G01V 1/001 Acoustic presence detection

Abstract

A non-invasive method for easily locating an underground septic tank, distribution box, field line, conduit, or underground cavity is disclosed. In a preferred embodiment, prescribed acoustic signals are injected into an underground cavity via an accessible port and remotely detected by a time synchronized detector in contact with the ground which cross correlates the detected signal with a duplicate of the prescribed acoustic signal in order to reject background noise, and thus locate the underground cavity. A frequency sweep is conducted to exploit cavity resonance modes and thus further enhance the signal to noise ratio.

Claims

1. A method comprising the steps of:

(a) generating a prescribed acoustic wave wherein a frequency f of said acoustic wave matches at least one resonant mode of an underground device including a cavity for at least a time equal to 2/f;

(b) acoustically injecting said acoustic wave into said underground device;

(c) establishing a first time reference in a first clock, wherein said first clock governs the generation of said acoustic wave;

(d) electronically detecting said acoustic wave, at a remote location in acoustic communication with said underground device through an earth path to produce a measurement of said acoustic wave;

(e) establishing a second time reference in a second clock, wherein said second time reference of said second clock is synchronized with said first time reference of said first clock, and said second clock governs said measurement;

(f) digitizing and storing a sequential series of measurements of said acoustic wave;

(g) performing digital processing on said series of measurements, wherein said digital processing comprises cross correlating said series of measurements with a priori amplitude values of said prescribed acoustic wave to produce a result related to the intensity of said acoustic wave at said remote location; and

(h) communicating said result to an operator.

2. The method of claim 1 wherein said underground device is a septic tank.

3. The method of claim 1 wherein said underground device is a fuel tank.

4. The method of claim 1 wherein said acoustically injecting is through a vent stack, cleanout, drain, or toilet.

5. The method of claim 1 wherein said first time reference and said second time reference are based at least in part on a broadcast time reference.

6. The method of claim 5 wherein the broadcast time reference is traceable to The National Institute of Standards and Technology.

7. The method of claim 1 wherein said electronically detecting is based at least in part on a geophone or an accelerometer.

8. The method of claim 1 wherein said result is used to locate said underground device.

9. The method of claim 1 further comprising a step of determining a time delay τ

of said acoustic wave at said remote location.

10. The method of claim 1 further comprising a step of determining a transfer function g(f) of said acoustic wave.

11. The method of claim 10 further comprising a step of determining at least one characteristic of a physical system based at least in part on said transfer function g(f).

12. The method of claim 11 wherein said at least one characteristic of a physical system is a distance between a liquid level and a septic tank lid.

13. The method of claim 11 wherein said at least one characteristic of a physical system is at least one dimension of said underground device.

14. The method of claim 1 wherein said frequency f is a predefined sequence of tones.

15. The method of claim 14 wherein said predefined sequence of tones is a frequency sweep over a range of tones selected to pass through a plurality of resonant vibrational modes;

and

wherein said frequency sweep is periodically repeated.