POSITIONING SYSTEM

• US 20100061187A1
• Filed: 10/11/2007
• Published: 03/11/2010
• Est. Priority Date: 10/12/2006
• Status: Active Grant

• Current Assignee: Electromagnetic Geoservices ASA
• Original Assignee: Electromagnetic Geoservices ASA
• Inventors: Sodal, Audun
• Granted Patent: US 8,913,463 B2
• Time in Patent Office: Days
• US Class Current: 367/131
• CPC Class Codes: G01S 13/86 Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• CPC Class Codes: G01S 5/22 Position of source determined by co-ordinating a plurality of position lines defined by path-difference measurements G01S5/28 takes precedence
• CPC Class Codes: G01V 1/001 Acoustic presence detection

Abstract

A passive listening acoustic system and method of use may include source means for providing continuous, pulsed, or pulse coded acoustic signals at two or more frequencies and at least two acoustic sensors or hydrophones which detect and record a signal for use within a Seabed Logging system to determine the position and/or orientation of instruments in the system.

Claims

1. A passive listening acoustic system, comprising:

source means for providing continuous, pulsed, or pulse coded acoustic signals at two or more different frequencies; and

at least two acoustic sensors or hydrophones, said acoustic sensors or hydrophones comprising means for detecting said acoustic signals and means for recording a detected signal.

2. A Seabed Logging system comprising:

an electromagnetic source;

at least one electromagnetic receiver; and

a passive listening acoustic system, the passive listening acoustic system comprising;

source means for providing continuous, pulsed, or pulse coded acoustic signals at two or more different frequencies; and

at least two acoustic sensors or hydrophones, said acoustic sensors or hydrophones comprising means for detecting said acoustic signals and means for recording a detected signal.

3. The system of claim 2, wherein the acoustic sensors or hydrophones are disposed to the electromagnetic receiver.

4. The system of claim 2, wherein the electromagnetic receiver is carried on a rigid frame, the at least two acoustic sensors or hydrophones being disposed to said frame.

5. The system of claim 4, wherein the at least two acoustic sensors or hydrophones are positioned on opposite sides of the frame.

6. The system of claim 2, further comprising at least one transponders disposed to the electromagnetic source or the electromagnetic receiver.

7. The system of claim 2, further comprising a sensor for measuring depth, tilt, or pitch.

8. The system of claim 2, wherein the electromagnetic receivers includes a magnetic sensor.

9. A method of determining the position of a towed electromagnetic source and at least one electromagnetic receiver for use in a Seabed Logging survey, the receiver including at least one acoustic sensor or hydrophone closely associated with the electromagnetic sensor, the method comprising:

dropping the electromagnetic receiver into sea water;

allowing the electromagnetic receiver to sink to a seafloor;

activating a first acoustic source at a first source signal;

measuring position, time, and movement of the first acoustic source;

activating a second acoustic source at a second source signal;

measuring position, time, and movement of the second acoustic source;

simultaneously recording detected acoustic signals on the at least one acoustic sensor or hydrophone at both the first and second signals; and

passing measured data to a central computer to calculate a phase difference or an arrival time between pairs of hydrophones.

10. The method of claim 9, further comprising towing the first acoustic source at a distance from the sea floor of between approximately 5 meters and approximately 100 meters.

11. The method of claim 9, further comprising providing at least one transponder, the transponder being disposed to the electromagnetic receiver.

12. The method of claim 9, further comprising providing one or more components selected from the group consisting of an orientation sensor, a depth sensor, a tilt sensor, a pitch sensor, a magnetic sensor, and the hydrophone, the one or more components being attached to a frame for carrying the electromagnetic receiver.

13. The method of claim 9, further comprising providing a third acoustic source.

14. The method of claim 9, further comprising towing the first and second acoustic sources on an electromagnetic source streamer behind a vessel.

15. The method of claim 13, further comprising positioning at least one of the first and second acoustic sources on an electromagnetic source streamer, the method further comprising towing the first and second acoustic sources on separate steamers.

16. The method of claim 13, further comprising positioning at least one of the first and second acoustic sources on a surface vessel or on a separate towed body close related to positioning of the surface vessel.

17. The method of claim 9, further comprising:

recording the phase measurements; and

storing the phase measurements, as time-stamped data in the system.

18. The method of claim 17, further comprising processing the phase measurements on the surface vessel after survey data has been collected and downloaded.

19. The method of claim 9, further comprising selecting at least one of the first and second acoustic signals from the group consisting of continuous, pulsed or coded signals.

20. The method of claim 19, wherein the coded signals are up- or down-sweep signals (Chirp signals) or spread spectrum or phase shifted code.

21. The method of claim 10, further comprising towing the first acoustic source or the second acoustic source is towed at a distance from the sea floor of between approximately 20 meters and approximately 30 meters.