Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
1999-06-11
2001-07-03
Oda, Christine K. (Department: 2862)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C367S149000
Reexamination Certificate
active
06256588
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of seismic sensor arrays and, more particularly, to a hydrophone or geophone sensor array that receives an acoustic signal, develops an electrical signal representative of the acoustic signal, and, through a plurality of electrical-to-optical transformers, converts the electrical signal to an optical signal for transmission to a central receiver.
BACKGROUND OF THE INVENTION
In seismic exploration, whether on land, at sea, or in a transition zone, large numbers of sensors are coupled together in groups to receive an acoustic signal and send a signal to a central receiver for detection. This signal is representative of geological structures which are analyzed for the likelihood of bearing hydrocarbons.
The presentation of such geological structures with adequate clarity and resolution requires large quantities of data. This data must be acquired over a long seismic cable or marine seismic streamer and conducted back to the central receiver. Current systems use optical fibers to carry the vast quantities of data due to the relatively large bandwidth of fiber optics and their relative immunity to many kinds of electromagnetic interference.
One of the weak links in the system just described is the portion which takes the acoustic signal and develops a signal for transmission to the central receiver. Recent developments have focused on fiber-optic sensors, so that the acoustic signal itself is used as the modulation means, creating a time varying effect on the optical path length of an optical fiber under the influence of the acoustic signal. These systems have proved to be effective, but technical developments remain before they reach large scale manufacture. In the meantime, there remains a need for some means to use the electrical signal from a conventional sensor, such as a hydrophone or a geophone, and convert that electrical signal into a useful optical signal for transmission to the central receiver and/or a recording medium.
SUMMARY OF THE INVENTION
The present invention addresses this need in the art by providing a means for passive electrical to optical energy transformation and transmission. This transformation is used remotely with traditional sensor arrays, which may include hydrophones, geophones, or a combination of them. The transformation means is used to develop an optical signal in a fiber which then conveys the seismic signals via a signal conditioner to a recording center or data accumulator.
In one aspect of the present invention, the system, including an optical fiber, a source, and a receiver, passively and remotely interrogates a plurality of electrical sensor strings by the use of electrical to fiber optical energy transformers, which are located at spatial nodes along a fiber optic transmission bus. Each node may constitute one seismic data channel.
The present invention is particularly adapted for use with network arrays and architectures of traditional seismic sensors. Any of the known configurations of sensor strings may be passively and remotely interrogated with this invention.
A feature the invention is the electrical to fiber optical transformer. This transformer is a device that converts electrical energy to mechanical energy that in turn modulates the amplitude and/or phase of optical energy traveling within an optical fiber wave guide bus cable. This cable may have only optical fibers, a strength member and a protective outer jacketing with discretely placed nodal takeouts where the optical fiber is tapped into.
In a preferred embodiment, mechanical strain of a single mode fiber waveguide modulates the phase of a propagating light wave within the fiber core and/or cladding at each node. In optical fiber technology, single mode fiber is optical fiber that is designed for the transmission of a single ray or mode of light as a carrier and is used for long-distance signal transmission. This modulation takes place with respect to a reference leg or compensating section of a fiber optic interferometer. Various forms of channel multiplexing on a given fiber bus may be employed. These multiplexing methods may include the domains of time, wavelength, frequency, phase, coherence, polarization, etc. In other embodiments, a multimode fiber may be employed.
In operation, a conventional electrical sensor array is deployed in the traditional fashion with each seismic channel (typically a plurality or string of such electrical phones) electrically connected to its respective transformation node along the fiber optic bus line. In this embodiment, no remote electrical power source, data concentration boxes, analog-to-digital converters, heavy copper transmission cable, or other remote data acquisition components are required. This approach provides for totally electrically passive remote interrogation of the seismic sensor array via low-cost, lightweight, all-dielectric optical fiber cable and other ancillary state-of-the-art optical narrow/broadband sources, receivers, couplers, connectors, switches, filters, gratings, isolators, circulators, reflectors, and modulators.
These and other features of this invention will be apparent to those skilled in the art from a review of the following detailed description.
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Craig Gary J.
Erath Louis W.
Luscombe John
Maida, Jr. John L.
Bracewell & Patterson L.L.P.
Geosensor Corporation
Oda Christine K.
Taylor Victor J.
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