Abstract: The invention relates to a hydrophone housing. The housing comprises an outer casing with an exterior shape being in close contact with sediment when buried therein and having a deflectable wall part. Solid material partly fills the casing to define an outer chamber behind the deflectable wall part, a cavity shaped so that an inner chamber is defined immediately surrounding a hydrophone sensing element held therein, and a first duct for liquid flow communication between the outer chamber and the cavity or an internal volume of the hydrophone sensing element. Thereby, a hydraulic coupling is provided so that an acoustic pressure causing small radial displacements of outer surface of the housing will, via liquid in the first duct, cause large radial displacements of the hydrophone sensitive element.

Abstract: The invention relates to a method of interrogating an interferometric optical fiber sensor system including a laser source configured to generate interrogation light and a sensor array with at least a first reflector and a second reflector.

Abstract: A subsea installation tool for installing a flexible body, e.g. a subsea fiber cable on a seabed from a surface vessel, and an associated method for installing the flexible body on the seabed is provided. The installation tool includes a tensioner that may be coupled to the flexible body to actively pull it down, thus increasing tension in an upper section of the cable from the installation vessel to the installation tool. High tension in the upper part of the cable gives good control even in strong sea currents. At the same time the tensioner enables lower tension in the bottom part cable from the installation tool to the seabed, giving good control of the touchdown position on the seabed.

Abstract: The invention relates to a method of interrogating an interferometric optical fibre sensor system including a laser source configured to generate interrogation light and a sensor array with at least a first reflector and a second reflector.

Abstract: A method of processing data from a distributed fibre-optic interferometric sensor system for measuring a measurand, the system comprising multiple interferometric sensors. The method comprises interrogating two or more of the multiple interferometric sensors to record a raw measurement time series for each of the sensors. The method further comprises calculating a common reference time series as a measure of central tendency of the raw measurement time series from two or more reference sensors, the reference sensors being selected from the multiple interferometric sensors. Finally, the method comprises compensating at least one raw measurement time series from a measurement sensor selected from the multiple interferometric sensors with the common reference time series to produce a compensated measurement time series, the measurement sensor being configured to be sensitive to the measurand. The invention further relates to a distributed fibre-optic interferometric sensor system.

Abstract: There is provided a solid seismic streamer cable for use in seismic surveying in marine environments. The streamer is characterized by a buffer layer 2 which is provided with a cut-out 50 and a sensor element arranged in the cut-out 50. There is also provided an associated hydrophone for integration into the seismic streamer cable. The hydrophone is characteristic in a split-element sensor base 10, 11 being suited for efficient mounting into the cut-outs 50 of the seismic cable. There is also provided an associated accelerometer for integration into the seismic streamer cable. The accelerometer is characteristic by a split-element sensor base 30, 35 for being efficiently arranged into the cut-outs 50 of the seismic cable. A method of producing a seismic streamer cable according to the invention incorporating a hydrophone or accelerometer according to the invention is also provided.

Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: A rotary joint or swivel device for ensuring a continuous connection between two items that rotates with respect to each other, for example between an instrumentation unit on a fixed installation and sensor elements in a cable on a rotating cable reel or drum, is provided. The rotary joint or swivel device comprises a minimum of two spools 1A,B to coil a connecting cable 3. A first spool 1A is coupled to a first, static, item 40. A second spool 1B is coupled to a second, rotatable, item 30. A guiding arm 4 feeds the connecting cable 3 from the first 1A to the second 1B spool. Correspondingly, a method for ensuring a continuous connection between two items 30,40 that rotates with respect to each other is provided. The method comprises arranging a rotary joint or swivel device according to any of the embodiments of the invention between the two items.

Abstract: There is provided a solid seismic streamer cable for use in seismic surveying in marine environments. The streamer is characterized by a buffer layer 2 which is provided with a cut-out 50 and a sensor element arranged in the cut-out 50. There is also provided an associated hydrophone for integration into the seismic streamer cable. The hydrophone is characteristic in a split-element sensor base 10, 11 being suited for efficient mounting into the cut-outs 50 of the seismic cable. There is also provided an associated accelerometer for integration into the seismic streamer cable. The accelerometer is characteristic by a split-element sensor base 30, 35 for being efficiently arranged into the cut-outs 50 of the seismic cable. A method of producing a seismic streamer cable according to the invention incorporating a hydrophone or accelerometer according to the invention is also provided.

Abstract: Container systems used in storage, deployment or retrieval of a seismic cable array comprise a container, at least two coiling elements attached to a bottom side of the container, and storage means for allocating or accommodating, in an ordered arrangement, a number of seismic stations and/or a number of couplers/splices and/or other discontinuities which are being interconnected by sections of the seismic cable. Said storage means is arranged between said coiling elements and are attached to the bottom side of the container. The seismic cable is spooled or wound around said coiling elements. Corresponding methods of storing a seismic cable and deploying/retrieving the seismic cable are based on the use of at least two coiling elements and storage means for allocating or accommodating a number of seismic stations and/or a number of couplers/splices and/or a number of other discontinuities and arranged between said coiling elements.

Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: There is provided a solid seismic streamer cable for use in seismic surveying in marine environments. The streamer is characterised by a buffer layer 2 which is provided with a cut-out 50 and a sensor element arranged in the cut-out 50. There is also provided an associated hydrophone for integration into the seismic streamer cable. The hydrophone is characteristic in a split-element sensor base 10, 11 being suited for efficient mounting into the cut-outs 50 of the seismic cable. There is also provided an associated accelerometer for integration into the seismic streamer cable. The accelerometer is characteristic by a split-element sensor base 30, 35 for being efficiently arranged into the cut-outs 50 of the seismic cable. A method of producing a seismic streamer cable according to the invention incorporating a hydrophone or accelerometer according to the invention is also provided.

Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: A tri-axis accelerometer for use in seismic surveying is provided. The accelerometer comprises at least three fiber optic accelerometer elements which have respective fiber sensor coils, and which are characteristic in that the fiber sensor coils are coiled about a common coiling axis and at least one of the accelerometer elements is a slant angle accelerometer element. A corresponding method of manufacturing a tri-axis fiber optic accelerometer is also disclosed. A fiber optic tri-axis accelerometer for sensing acceleration in three directions is also provided, which comprises a first, a second, and a third sensor base, each base including a first, a second, and a third fixed element, respectively, and a first, a second, and a third movable element, respectively, each pair of fixed and movable elements carrying a fiber sensing coil.

Abstract: There is provided a solid seismic streamer cable for use in seismic surveying in marine environments. The streamer is characterised by a buffer layer 2 which is provided with a cut-out 50 and a sensor element arranged in the cut-out 50. There is also provided an associated hydrophone for integration into the seismic streamer cable. The hydrophone is characteristic in a split-element sensor base 10, 11 being suited for efficient mounting into the cut-outs 50 of the seismic cable. There is also provided an associated accelerometer for integration into the seismic streamer cable. The accelerometer is characteristic by a split-element sensor base 30, 35 for being efficiently arranged into the cut-outs 50 of the seismic cable. A method of producing a seismic streamer cable according to the invention incorporating a hydrophone or accelerometer according to the invention is also provided.

Abstract: 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.

Abstract: Methods and apparatus for cable termination and sensor integration at a sensor station within an ocean bottom seismic (OBS) cable array are disclosed. The sensor stations include a housing for various sensor components. Additionally, the sensor stations can accommodate an excess length of any data transmission members which may not be cut at the sensor station while enabling connection of one or more cut data transmission members with the sensor components. The sensor stations further manage any strength elements of the cable array.

Abstract: Methods and apparatus for interrogating optical sensors with high slew rates using non-uniform sampling are provided. The transmission of optical signals in a non-uniform pattern is employed to allow for demodulation of fringe rates exceeding the commonly understood Nyquist frequency limit given as one half of the mean sampling frequency. By monitoring the time dependent fringe frequency and assuming that the fringe frequency has a limited bandwidth, only a limited bandwidth smaller than the Nyquist bandwidth around the instantaneous fringe frequency needs to be reconstructed at any time.

Abstract: A method and apparatus for demodulation of detected fringes from interferometric sensors with high slew rates are provided. A detected interference signal may be mixed with a local oscillator phasor to obtain a mixed signal, the local oscillator being controlled to produce a frequency that roughly matches the fringe frequency of the interference signal. A sensor phase estimate may be obtained from the detected interference signal or the mixed signal. The local oscillator signal can be computed from the sensor phase estimate. The mixed signal and the sensor phase estimate may be low pass filtered and decimated and the resulting decimated mixed signal and decimated sensor phase estimate may be processed and combined with moderate processing power requirements in an effort to accurately measure the sensor phase for the interferometric sensor.

Abstract: 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.