Sensing System

• US 20080219093A1
• Filed: 03/02/2006
• Published: 09/11/2008
• Est. Priority Date: 03/04/2005
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: EMC Corporation (Dell Technologies Inc.)
• Inventors: Tateson, Jane E, Heatley, David J T
• Granted Patent: US 7,755,971 B2
• Time in Patent Office: Days
• US Class Current: 367/16
• CPC Class Codes: G01V 1/16 Receiving elements for seismic signals; Arrangements or adaptations of receiving elements
• CPC Class Codes: G01V 1/3808 Seismic data acquisition, e.g. survey design

Abstract

The present invention relates to a sensing system, in particular to sensing system for sensing undersea seismic events. A vibration sensor is provided for sensing seismic vibrations on the sea bed is provided. The vibration sensor is electrically coupled to a transmitter unit, the transmitter unit being arranged to transmit, in use, an acoustic wave from which the presence of a seismic vibration can be inferred. The acoustic wave modulates light travelling along a nearby optical cable, the modulation being recovered at a distant monitoring station. A flotation arrangement is provide for retaining the transmitter unit in a raised position relative to the sea bed to facilitate the coupling of the acoustic wave to the optical cable.

Claims

1. An undersea seismic sensing system including:

a vibration sensor for sensing seismic vibrations on the sea bed;

a transmitter unit coupled to the vibration sensor, the transmitter unit being arranged to transmit, in use, an acoustic wave from which the presence of a seismic vibration can be inferred; and

, a flotation arrangement for retaining the acoustic transmitter unit in a raised position relative to the sea bed.

2. An undersea seismic sensing system as claimed in claim 1, wherein the flotation arrangement includes a buoyancy unit secured to the transmitter unit so as to urge the transmitter unit in an upward direction.

3. An undersea seismic sensing system as claimed in claim 1, wherein there is provided a tether arrangement for securing the transmitter unit to the sea bed.

5. An undersea seismic sensing system as claimed in claim 1, wherein the transmitter unit is arranged to transmit acoustic waves in a generally downward direction.

6. A communications system including:

an undersea seismic sensor system as claimed in any of the preceding claims;

an optical cable arranged such that, in use, the acoustic wave from the transmitter unit modulates the phase of light travelling along the optical cable; and

, a monitoring station for extracting information indicative of a seismic vibration from the phase modulated light.

4. An undersea seismic sensing system as claimed in claim 4, wherein the tether arrangement includes a weighted base.

7. A method of sensing an undersea seismic disturbance, including the steps of:

sensing seismic vibrations on the sea bed using a vibration sensor, the vibration sensor being coupled to a transmitter unit;

transmitting from the transmitter unit an acoustic signal from which the presence of a seismic vibration can be inferred, the transmitter unit being retained in a raised position relative to the sea bed; and

detecting the acoustic signal at an optical link.

8. A method of sensing an undersea seismic disturbance as claimed in claim 7, wherein the acoustic signals cause a phase modulation of optical signals travelling along the optical link.

9. A method of sensing an undersea seismic disturbance as claimed in claim 8, wherein the optical signals are formed by pairs of signal copies, which copies of a pair have a time delay relative to one another, and wherein the respective signals of a pair are combined so as to extract modulated data, if any, in the sensing signals from which the presence of a disturbance can be inferred.

10. A method of sensing an undersea seismic disturbance as claimed in claim 9, wherein the time delay is greater than the inverse of the frequency of the modulation.

11. A communication system including a transmitter unit having an acoustic transmitter for transmitting acoustic waves through a fluid medium;

an optical link arranged such that the acoustic waves modulate light travelling along the link; and

a monitoring station for detecting the modulation.