Detection of Moving Objects

• US 20130151203A1
• Filed: 08/15/2011
• Published: 06/13/2013
• Est. Priority Date: 08/16/2010
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Inventors: McEwen-King, Magnus, Hill, David John, Godfrey, Alastair
• Granted Patent: US 10,352,763 B2
• Time in Patent Office: Days
• US Class Current: 702/189
• CPC Class Codes: G01H 9/004 using fibre optic sensors light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125
• CPC Class Codes: G06F 17/00 Digital computing or data processing equipment or methods, specially adapted for specific functions information retrieval, database structures or file system structures therefor G06F16/00

Abstract

A system for moving object (402) detection is provided, the system comprising a fibre optic interrogator (106) adapted to provide distributed acoustic sensing on a optic fibre (104), for example arranged along a border. The measurement signals from each of a plurality of sensing portions (404, 406, 408, 410, 412) of said fibre are analysed to determined a characteristic of a Doppler shift. The characteristic of a Doppler shift may be a generally continuous decrease in detected frequency. By detecting the time at which the rate of change of frequency is at a maximum for each of the sensing portions the time of closest approach (ti, t2, t3, t4, t5) of the object to those sensing portions can be determined with the sensing portion the object approaches closest to showing the greatest value of maximum rate of change of frequency. The distance of closest approach and velocity can be determined.

Claims

1. A distributed acoustic sensor apparatus comprising:

an interrogator unit for, in use, interrogating an optical fibre with optical radiation and producing a measurement signal indicative of incident acoustic signals from each of a plurality of sensing portions of said optical fibre; and

a processor configured to analyse said measurement signals to identify a signal characteristic of a Doppler shift so as to detect a moving object.

3. An apparatus as claimed in claim 1 wherein said characteristic of a Doppler shift comprises a decrease in the frequency of detected signal at a particular sensing portion of optical fibre over time.

5. An apparatus as claimed in claim 1 wherein said characteristic of a Doppler shift comprises detection of signals of different frequency at different sensing portions of the optical fibre which are spatially separated.

6. An apparatus as claimed in claim 1 wherein the processor is configured to analyse the characteristic of a Doppler shift to detect the range and/or location of the object relative to the sensing fibre.

7. An apparatus as claimed in claim 6 wherein the processor is configured to analyse the measurement signals from a plurality of sensing portions to determine the time at which the maximum rate of change of frequency occurs for each sensing portion.

8. An apparatus as claimed in claim 7 wherein the time at which the maximum rate of change of frequency occurs for each sensing portion is used to determine the time at which the object was closest to that sensing portion.

9. An apparatus as claimed in claim 8 wherein the processor is adapted to use the times at which each sensing portion detects signals from the point of closest approach of that object to track the movement of the object along the fibre.

10. An apparatus as claimed in claim 7 wherein the processor is configured to determine the value of the maximum rate of change of frequency for each of a plurality of sensing portions.

11. An apparatus as claimed in claim 10 wherein the processor is configured to determine the sensing portion for which the measurement signal has the greatest value of maximum rate of change of frequency out of any sensing portion and to identify such sensing portion as the sensing portion which the object passed closest to.

12. An apparatus as claimed in claim 7 wherein the processor is configured identify the frequency of the measurement signal corresponds to the maximum value of rate of change of frequency as the true frequency of the acoustic signal emitted by the object.

13. An apparatus as claimed in claim 12 wherein the processor is configured to use the true frequency to determine the relative velocity of the object.

14. An apparatus as claimed in claim 7 wherein the processor is configured to determine the distance of closest approach of the object to a sensing portion by analysing the maximum rate of change of frequency.

16. An apparatus as claimed in claim 1 wherein, having detected an object, the processor is configured to analyse the characteristics of the signals from a plurality of sensing portions to detect characteristics associated with a change in motion.

17. An apparatus as claimed in claim 16 wherein said characteristics associated with a change in motion comprise a change in location of the sensing portion that exhibits a local maximum or minimum in frequency of the measurement signal.

18. An apparatus as claimed in claim 16 wherein said characteristics associated with a change in motion comprise a sudden increase or decrease in frequency of the measurement signal from several sensing portions.

20. An apparatus as claimed in claim 1 wherein the processor is configured to analyse the time of arrival of acoustic signals emitted from the object at different locations of the optical fibre and/or distance of closest approach of an object to different locations of the optical fibre to avoid any positional ambiguity in the location of the object.

21. An apparatus as claimed in claim 1 wherein the processor is configured to receive data from at least one other sensor to avoid any positional ambiguity in the location of the object.

22. An apparatus as claimed in claim 1 wherein the processor is configured to analyse said measurement signals to detect signals characteristic of an aircraft.

23. An apparatus as claimed in claim 22 wherein said signals characteristic of an aircraft are tonal measurement signals from a predetermined number of the plurality of sensing portions.

2. (canceled)

4. (canceled)

15. (canceled)

19. (canceled)

24-29. -29. (canceled)

30. A method of distributed acoustic sensing comprising:

interrogating an optical fibre with optical radiation and producing a measurement signal indicative of incident acoustic signals from each of a plurality of sensing portions of said optical fibre; and

analysing said measurement signals to identify a signal characteristic of a Doppler shift so as to detect a moving object.

31. A method as claimed in claim 30 wherein said optical fibre is deployed along the length of the border or perimeter and said method comprises monitoring of said border or perimeter.

36. A method as claimed in claim 30 comprising detecting an acoustic signal from an acoustic transmitter located on the object.

37. A method as claimed in claim 36 comprising fitting an object to be detected with an acoustic transducer arranged to produce an acoustic output at a defined frequency.

32-35. -35. (canceled)

38. A method of processing data acquired from a distributed acoustic sensor to detect moving objects comprising taking data comprising measurement signals indicative of incident acoustic signals from each of a plurality of sensing portions of a distributed acoustic sensor;

and analysing said measurement signals to identify a signal characteristic of a Doppler shift so as to detect a moving object.