Seismic streamer array
Seismic sensor systems and sensor station topologies, as well as corresponding cable and sensor station components, manufacturing and deployment techniques are provided. For some embodiments, networks of optical ocean bottom seismic (OBS) stations are provided, in which sensor stations are efficiently deployed in a modular fashion as series of array cable modules deployed along a multi-fiber cable.
1. A seismic streamer array, comprising:
a submersible cable with buoyancy to suspend the submersible cable in water;
one or more series of sensor groups, each group having a plurality of optical sensors sharing a common wavelength, the common wavelength being different for each group in a same series;
instrumentation coupled to the series of sensor groups and configured to interrogate sensors in each group using time division multiplexing (TDM) and to interrogate sensors in different sensor groups in each series using wavelength division multiplexing (WDM);
a module connection node for each series of sensor groups; and
a lead cable with multiple fibers coupling the instrumentation to the one or more series of sensor groups, wherein each module connection node couples a different one or more of the multiple fibers of the lead cable to a sensor fiber used to interrogate a series of sensor groups.
2. The system of claim 1 , wherein light at wavelengths interrogating one or more groups in a series passes through a plurality of sensors of at least one other group.
3. The system of claim 1 , wherein the groups comprise an optical fiber section for each sensor, the optical fiber sections being separated by partial reflectors that have a relatively high first reflectivity for light at the common wavelength of the corresponding group and a relatively low second reflectivity, substantially lower than the first reflectivity, for light at the common wavelengths of other groups in the same series.
4. The system of claim 3 , wherein the partial reflectors comprise Bragg gratings.
5. The system of claim 1 , wherein each series of sensor groups comprise hydrophones spaced along the submersible cable.
6. The system of claim 1 , wherein each series of sensor groups comprise electro-magnetic sensors.
7. The system of claim 1 , further comprising a steering device disposed along the submersible cable.
8. The system of claim 1 , wherein the multiple fibers are carried in a separate tube from the sensor fiber.
9. The system of claim 1 , wherein:
the one or more series of sensor groups are located below a sea surface and above a sea bed; and
the instrumentation is located above the sea surface.
10. The system of claim 1 , wherein the one or more series of sensor groups are located below a sea surface and above a sea bed.
11. A method of gathering seismic data from a series of seismic sensor groups, each group having a plurality of optical sensors sharing a common wavelength, the common wavelength being different for each group in a same series, the method comprising:
providing a seismic streamer array, the array comprising:
a submersible cable with buoyancy and having the plurality of optical sensors disposed along its length;
a lead cable with multiple fibers coupling instrumentation to the series of sensor groups; and
a module connection node for each series of sensor groups, wherein each module connection node couples a different one or more of the multiple fibers of the lead cable to a sensor fiber used to interrogate a series of sensor groups;
suspending the submersible cable in water;
interrogating, via a common optical path, sensors in each group using time division multiplexing (TDM) while the submersible cable is suspended; and
interrogating, via the common optical path, sensors in different sensor groups in each series using wavelength division multiplexing (WDM) while the submersible cable is suspended.
12. The method of claim 11 , wherein interrogating, via a common optical path, sensors in each group using time division multiplexing (TDM) comprises interrogating a reference interferometer in a sensor group and positioned earlier in the common optical path than other sensors in the same sensor group.
13. The method of claim 11 , wherein the sensors in each group are interferometric sensors and interrogating the sensors in each group using TDM comprises generating a pulse pair with a spacing between pulses corresponding to a common sensor delay.
14. The method of claim 13 , wherein the interferometric sensors comprise Fabry-Perot type interferometers using wavelength dependent reflectors.
15. The method of claim 14 , wherein the wavelength dependent reflectors comprise Bragg gratings.
16. The method of claim 11 , wherein interrogating sensors in different sensor groups in each series using wavelength division multiplexing (WDM) comprises generating the pulse pair with different wavelength components corresponding to wavelengths of different sensor groups in the series.