Enhanced sonde recognition

• US 20070084636A1
• Filed: 10/14/2005
• Published: 04/19/2007
• Est. Priority Date: 10/14/2005
• Status: Active Grant

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Royle, John
• Granted Patent: US 7,567,875 B2
• Time in Patent Office: Days
• US Class Current: 175/45
• CPC Class Codes: G01V 3/08 operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices with electromagnetic waves G01V3/12

Abstract

A detector for locating a sonde is comprised of a plurality of antennas, a corresponding number of signal isolator modules 1 and a geometrical evaluation module. The magnetic signal generated by the sonde has a fundamental frequency and harmonic frequencies. A frequency spectrum analyser 29 which forms part of the signal isolator module 1 has frequency bins which are aligned with the fundamental frequency and a plurality of harmonic frequencies of the magnetic signal produced by the sonde. The frequency bins follow variations in the frequency of the magnetic signal produced by the sonde which allows the detector to detect the sonde at a separation of up to 30 m.

Claims

1. A detector for detecting an oscillating magnetic signal produced by a sonde, the magnetic signal having a fundamental frequency and harmonic frequencies, the detector comprising a frequency spectrum analyser having frequency bins and an output, wherein the frequency bins of the frequency spectrum analyser are substantially aligned with the fundamental frequency and a plurality of the harmonic frequencies of the magnetic signal produced by the sonde.

2. A detector as claimed in claim 1, wherein the frequency bins are adapted to follow frequency variation of the magnetic signal produced by the sonde.

3. A detector as claimed in claim 1, wherein the output from the spectrum analyser is passed to a matched filter which produces a rank correlation coefficient.

4. A detector as claimed in claim 3, wherein the output from the matched filter is passed to an arbitrator which decides whether the sonde is detectable by the detector or not.

5. A detector as claimed in claim 1, wherein the frequency spectrum analyser comprises a complex discrete Fourier transform.

6. A detector as claimed in claim 5, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 20 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

7. A detector as claimed in claim 5, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 1 OmHz of the fundamental frequency of the magnetic signal produced by the sonde.

8. A detector as claimed in claim 5, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 5 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

9. A detector as claimed in claim 5, the output of the frequency spectrum analyser being comprised of measurements of the fundamental frequency and harmonic frequencies of the magnetic signal produced by the sonde and measurements of noise, allowing a signal to noise ratio to be calculated for the fundamental frequency and harmonic frequencies, wherein the signal to noise ratio for at least 4 of the harmonic frequencies is greater than 6 dB.

10. A detector as claimed in claim 5, wherein the signal to noise ratio for at least 8 of the harmonic frequencies is greater than 6 dB.

11. A detector as claimed in claim 1, wherein the signal to noise ratio for at least 16 of the harmonic frequencies is greater than 6 dB.

12. A method of detecting an oscillating magnetic signal produced by a sonde, the magnetic signal having a fundamental frequency and harmonic frequencies, the method comprising analysing the frequency spectrum of the magnetic signal with a frequency spectrum analyser having frequency bins and an output, wherein the frequency bins of the frequency spectrum analyser are substantially aligned with the fundamentalfrequency and a plurality of the harmonic frequencies of the magnetic signal produced by the sonde.

13. A method as claimed in claim 12, wherein the frequency bins follow frequency variation of the magnetic signal produced by the sonde.

14. A method as claimed in claim 12, wherein the output from the spectrum analyser is filtered to produce a rank correlation coefficient.

15. A method as claimed in claim 14, wherein the rank correlation coefficient is arbitrated to decide whether the sonde is detectable by the detector or not.

16. A method as claimed in claim 12, wherein the frequency spectrum analyser is as a complex discrete Fourier transform.

17. A method as claimed in claim 12, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 20 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

18. A method as claimed in claim 12, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 1 OmHz of the fundamental frequency of the magnetic signal produced by the sonde.

19. A method as claimed in claim 12, wherein one of the frequency bins of the frequency spectrum analyser is aligned within 5 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

20. A method as claimed in claim 12, the output of the frequency spectrum analyser being comprised of measurements of the fundamental frequency and harmonic frequencies of the magnetic signal produced by the sonde and measurements of noise, the method comprising measuring the signal to noise ratio of the fundamental frequency and harmonic frequencies, wherein the signal to noise ratio for at least 4 of the harmonic frequencies is greater than 6 dB.

21. A method as claimed in claim 12, wherein the signal to noise ratio for at least 8 of the harmonic frequencies is greater than 6 dB.

22. A method as claimed in claim 12, wherein the signal to noise ratio for at least 16 of the harmonic frequencies is greater than 6 dB.

23. A computer program for detecting an oscillating magnetic signal produced by a sonde, the magnetic signal having a fundamental frequency and harmonic frequencies, the computer program comprising analysing the frequency spectrum of the magnetic signal induced in an antenna with frequency spectrum analysis having frequency bins and an output, wherein the frequency bins of the frequency spectrum analysis are substantially aligned with the fundamental frequency and a plurality of the harmonic frequencies of the magnetic signal produced by the sonde.

24. A computer program as claimed in claim 23, wherein the frequency bins follow frequency variation of the magnetic signal produced by the sonde.

25. A computer program as claimed in claim 23, wherein the output from the spectrum analysis is filtered to produce a rank correlation coefficient.

26. A computer program as claimed in claim 25, wherein the rank correlation coefficient is arbitrated to decide whether the sonde is detectable by the detector or not.

27. A computer program as claimed in claim 23, wherein the frequency spectrum analysis is performed by a complex discrete Fourier transform.

28. A computer program as claimed in claim 23, wherein one of the frequency bins of the frequency spectrum analysis is aligned within 20 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

29. A computer program as claimed in claim 23, wherein one of the frequency bins of the frequency spectrum analysis is aligned within 10 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

30. A computer program as claimed in claim 23, wherein one of the frequency bins of the frequency spectrum analysis is aligned within 5 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

31. A computer program as claimed in claim 23, the result of the frequency spectrum analysis being comprised of measurements of the fundamental frequency and harmonic frequencies of the magnetic signal produced by the sonde and measurements of noise, the computer program comprising measuring the signal to noise ratio of the fundamental frequency and harmonic frequencies, wherein the signal to noise ratio for at least 4 of the harmonic frequencies is greater than 6 dB.

32. A computer program as claimed in claim 23, wherein the signal to noise ratio for at least 8 of the harmonic frequencies is greater than 6 dB.

33. A computer program as claimed in claim 23, wherein the signal to noise ratio for at least 16 of the harmonic frequencies is greater than 6 dB.

34. (canceled)

35. (canceled)