Abstract: A system (100) for monitoring a field (20) under a body of water, wherein the system (100) comprises a reference station (112) and a plurality of permanent seafloor sensors (120, 121). Each permanent seafloor sensor (120, 121) is fixed relative to a seafloor (2) on or at the field (20). The seafloor sensor (120, 121) further has a nearby survey station (111) sufficiently distant to ensure that a movable sensor (122) visiting the nearby survey station (111) does not disturb measurements from the permanent seafloor sensor (120). The distance is sufficiently close to ensure that the offset (?p, ?g) from a value provided by the permanent seafloor sensor (120) is constant or can be modelled, e.g. to account for changes in the pressure/depth relation due to changes in water density. Each seafloor sensor is associated with a unique drift function d(t) at least comprising a drift rate (a).

Abstract: A device (110) for performing measurements on a seabed (3), comprises a chamber (111) containing a sensor (120) and a fluid (115) at a constant temperature and at an ambient pressure. This removes the need for calibration in large ranges of both pressure and temperature. In addition, this eliminates the need to wait until the sensor (120) has achieved ambient temperature, and thereby achieves a desired accuracy of the recordings from the sensor while decreasing the operation time. The device preferably comprises an insulating layer (113), an internal temperature stabilising device (130) and a circulating device (131) to ensure a constant temperature and low temperature gradients within the chamber (111). The pressure within chamber (111) may be equalised to ambient pressure by a pressure inlet (112).

Abstract: A device (110) for performing measurements on a seabed (3), comprises a chamber (111) containing a sensor (120) and a fluid (115) at a constant temperature and at an ambient pressure. This removes the need for calibration in large ranges of both pressure and temperature. In addition, this eliminates the need to wait until the sensor (120) has achieved ambient temperature, and thereby achieves a desired accuracy of the recordings from the sensor while decreasing the operation time. The device preferably comprises an insulating layer (113), an internal temperature stabilising device (130) and a circulating device (131) to ensure a constant temperature and low temperature gradients within the chamber (111). The pressure within chamber (111) may be equalised to ambient pressure by a pressure inlet (112).

Abstract: A system (1) for operating a subsea sensor field (2), comprises an automated underwater vehicle—AUV (10) and a subsea service station (13). A sensor (11, 12) in the sensor field (2) comprises a permanently installed base unit (11) and a removable control unit (12). The AUV (10) moves control units (12) to the service station (13) for charging and updating, and then back to the base units.

Abstract: A system (1) for operating a subsea sensor field (2), comprises an automated underwater vehicle-AUV (10) and a subsea service station (13). A sensor (11, 12) in the sensor field (2) comprises a permanently installed base unit (11) and a removable control unit (12). The AUV (10) moves control units (12) to the service station (13) for charging and updating, and then back to the base units. The permanent positions of the base units (11) facilitate time-lapse surveys, and saves energy as heavy equipment may remain on the seafloor.

Abstract: A method for measuring subsidence and/or uprise on a field, comprises the steps of: deploying at least one cable on a solid surface; collecting inline tilt data from numerous tilt sensors deployed along each cable (100); and performing a statistical analysis on the tilt data to determine changes in curvature on the solid surface. Preferably, the statistical method involves computing a cumulative inline and/or cross-line tilt, whereby random errors cancel and systematic changes add. In addition, regression and/or interpolation may provide a quantitative estimate of curvature etc.

Abstract: A seismic ocean bottom cable array is provided for use in subsurface exploration. The array includes receiver stations for measuring seismic signals, and a cable including conductors for data transmission and an externally attached stress member. The array is assembled during deployment by attaching the data transmission cables and receiver stations to the stress member as it is lowered into the water.

Abstract: The invention describes a sensor array with digital signals transmitted over an optical fiber for seismic exploration systems. The seismic system includes a transducer for providing digital optical data signals and an optical interrogator for collecting the digital data. The transducer provides data from seismic sensors to the optical interrogator by acting on an optical carrier transmitted along the optical fiber. The system is designed to utilize known electromechanical seismic sensors with fiber optic telemetry.

Abstract: The invention describes a sensor array with digital signals transmitted over an optical fiber for seismic exploration systems. The seismic system includes a transducer for providing digital optical data signals and an optical interrogator for collecting the digital data. The transducer provides data from seismic sensors to the optical interrogator by acting on an optical carrier transmitted along the optical fiber. The system is designed to utilize known electromechanical seismic sensors with fiber optic telemetry.

Abstract: A preferred seismic survey system includes a cable having a sensor unit. The sensor unit includes sensors for detecting acoustical energy (e.g., shear and/or pressure waves) and is disposed in a decoupling device that substantially acoustically uncouples the sensor unit from the cable. One preferred decoupling device includes relatively flexible tension members that isolate the sensor unit from acoustical-energy related movement of the cable. A fastening member, which is optionally formed of vibration absorbing material, affixes the sensor unit to the flexible member. Optionally, a spacer adjusts the resonant frequency of the tension member and a resilient tube encloses the decoupling device. One preferred seismic survey method includes connecting the sensor unit to a cable with a decoupling device that substantially acoustically uncouples the sensor unit from the cable; and positioning a sensor unit on a seabed such that the sensor unit is acoustically coupled to the seabed.

Abstract: A seismic ocean bottom cable array is provided for use in subsurface exploration. The array includes receiver stations for measuring seismic signals, and a cable including conductors for data transmission and an externally attached stress member. The array is assembled during deployment by attaching the data transmission cables and receiver stations to the stress member as it is lowered into the water.