Enhanced sonde recognition

• US 7,310,584 B2
• Filed: 10/14/2005
• Issued: 12/18/2007
• Est. Priority Date: 10/14/2005
• Status: Expired due to Fees

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Royle, John Mark
• Primary Examiner(s): Barlow; John
• Assistant Examiner(s): LE, JOHN H
• Application Number:
  US11/249,745
• Publication Number:
  US 20070085698A1
• Time in Patent Office: 795 Days
• Field of Search: 702/65, 702/66, 702/75, 702/127, 702189-194, 702/197, 375/259, 375/232, 375/345, 324/326, 324/329, 340/572.5, 340/854, 340/333, 175/259, 175/45
• US Class Current: 702/65
• CPC Class Codes: G01V 3/26 operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device with electromagnetic waves G01V3/30

Abstract

A detector for locating a sonde includes a plurality of antennas, an analogue to digital converter 11 and a digital signal processor to isolate the magnetic signal produced by the sonde. The digital signal processor includes a phase feedback loop 21 to allow the digital processing unit to follow variations in the frequency of oscillation of the magnetic signal produced by the sonde.

Claims

1. A detector for detecting an oscillating magnetic signal produced by a sonde, the detector comprising:

a plurality of antennas for detecting electromagnetic signals with a plurality of frequencies comprising the magnetic signal produced by the sonde, each antenna having an analogue output;

an analogue to digital converter for sampling the analogue output of the antennas to produce a digital output; and

digital processing means, for processing the digital output from the analogue to digital converter to isolate the magnetic signal produced by the sonde, wherein the digital processing means comprises a phase feedback loop to allow the digital processing means to follow variations in the frequency of oscillation of the magnetic signal produced by the sonde,

wherein the digital processing means comprises a low-pass filter to isolate the magnetic signal produced by the sonde,

wherein the bandwidth of the low-pass filter is less than 0.5 Hz at −

140 dB,

the detector comprising a frequency spectrum analyzer having frequency bins and an output, wherein the frequency bins of the frequency spectrum analyzer are substantially aligned with a 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 analyzer 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 analyzer comprises a complex discrete Fourier transform.

6. A detector as claimed in claim 1, wherein one of the frequency bins of the frequency spectrum analyzer is aligned within 20 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

7. A detector as claimed in claim 1, wherein one of the frequency bins of the frequency spectrum analyzer is aligned within 10 mHz of the fundamental frequency of the magnetic signal produced by the sonde.

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

9. A detector as claimed in claim 1, the output of the frequency spectrum analyzer 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 1, 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 for detecting an oscillating magnetic signal produced by a sonde, the method comprising:

detecting electromagnetic signals with a plurality of frequencies comprising the magnetic signal produced by the sonde;

sampling the detected signal to produce a digital output;

processing the digital output with a digital signal processor to isolate the magnetic signal produced by the sonde;

converting the isolated signal to its magnitude and phase measurements; and

feeding back the phase of the isolated signal to allow the processor to follow variations in the frequency of oscillation of the magnetic signal produced by the sonde,

the magnetic signal having a fundamental frequency and harmonic frequencies, the method comprising analyzing the frequency spectrum of the magnetic signal with a frequency spectrum analyzer having frequency bins and an output, wherein the frequency bins of the frequency spectrum analyzer are substantially aligned with the fundamental frequency 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 analyzer is passed to a matched filter which produces a rank correlation coefficient.

15. A method as claimed in claim 14, wherein the output from the matched filter is passed to an arbitrator which decides whether the sonde is detectable by the detector or not.

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

17. A method as claimed in claim 12, wherein one of the frequency bins of the frequency spectrum analyzer 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 analyzer is aligned within 10 mHz 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 analyzer 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 analyzer 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 in a computer readable medium for detecting an oscillating magnetic signal produced by a sonde in an electromagnetic signal with a plurality of frequencies comprising the magnetic signal produced by the sonde, the computer program comprising:

sampling the electromagnetic signal to produce a digital output;

processing the digital output to isolate the magnetic signal produced by the sonde;

converting the isolated signal to its magnitude and phase measurements; and

feeding back the phase of the isolated signal to allow the processing to follow variations in the frequency of oscillation of the magnetic signal produced by the sonde,

the magnetic signal having a fundamental frequency and harmonic frequencies, the computer program comprising analyzing the frequency spectrum of the magnetic signal with a frequency spectrum analyzer having frequency bins and an output, wherein the frequency bins of the frequency spectrum analyzer 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 analyzer is passed to a matched filter which produces a rank correlation coefficient.

26. A computer program as claimed in claim 25, wherein the output from the matched filter is passed to an arbitrator which decides whether the sonde is detectable by the detector or not.

27. A computer program as claimed in claim 23, wherein the frequency spectrum analyzer comprises a complex discrete Fourier transform.

28. A computer program as claimed in claim 23, wherein one of the frequency bins of the frequency spectrum analyzer 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 analyzer 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 analyzer 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 output of the frequency spectrum analyzer 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.

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.