Sensor cable and multiplexed telemetry system for seismic cables having redundant/reversible optical connections

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#1. Field of the Invention

#FIG. 1 shows an example combination FDM/WDM telemetry system for a section in an array of seismic sensors.

#FIG. 1A shows an example of TDM/WDM telemetry system on two separate sensor cables.

#FIG. 2 shows an example system deployment of a plurality of sensor cables of the type shown in FIG. 1 or FIG. 1A.

#An optical sensor cable and a system according to various aspects of the invention are generally bi-directional, meaning that they can be coupled to a data acquisition device and/or to subsequent cables (or segments thereof) in either direction. An optical sensor cable and a system according to various aspects of the invention may also have redundant source light and signal return paths, such that in the event of failure of a source light fiber or a signal return fiber, or failure of a portion of a fiber, signal acquisition may still be performed using substantially all the sensors in the cable and system. Various examples of a sensor cable and system will now be described that may include such aspects of the invention.

#An example sensor cable that can be used with wavelength division multiplexed (“WDM”) and frequency division multiplexed (“FDM”) optical telemetry is shown schematically in FIG. 1. A sensor cable 10 may be a seismic sensor streamer arranged to be towed in a body of water by a seismic survey vessel. The cable 10 may also be a land-based seismic sensor cable deployed on the land surface, or an ocean bottom seismic sensor cable (“OBC”) deployed on the bottom of a body of water. The seismic sensor cable 10 can include one or more source light fibers 14 that may ultimately be coupled to a light source such as a laser diode and an associated modulator (as will be explained with reference to FIG. 2). Such light source may be disposed, for example, on a seismic vessel (not shown in the figures) or in a seismic recording system (50 in FIG. 2). The source light fibers 14 generally extend over the entire length of the sensor cable 10 and may include connectors (not shown separately) of types known in the art for coupling an optical sensor cable to another device.

#The seismic sensor cable 10 may also include one or more auxiliary source light fibers 16 extending substantially along the entire length of the cable 10. The purpose and configuration of the auxiliary source light fibers 16 will be further explained below. The seismic sensor cable 10 may include a plurality of optical seismic sensors, such as optical hydrophones and/or optical accelerometers (particle motion sensors). The seismic sensors are shown generally at 30. As shown in FIG. 1, the seismic sensors 30 may be arranged in groups, W1, W2, W3 disposed at spaced apart locations along the seismic sensor cable 10. In one example, each group W1, W2, W3 may include one optical hydrophone, and three, mutually orthogonally arranged optical particle motion sensors such as accelerometers. One example of a three-component optical accelerometer that may be used in some examples is described in U.S. Pat. No. 7,22,534 issued to Maas et al. and assigned to the assignee of the present invention. The seismic sensor cable 10 may include one or more signal return fibers 32 extending substantially along the entire length of the cable 10. The signal return fibers 32 are configured for returning optical signals from the seismic sensors 30 to the recording system (50 in FIG. 2) for decoding and interpretation. Devices for decoding and interpreting the signals from each of the optical sensors 30 are known in the art.