Provided is an aircraft 10 which has been configured for conducting airborne gravimetry surveys, comprising a gravimeter 14, a global navigation satellite system (GNSS) receiver 18 arranged in signal communication with the gravimeter 14, as well as a Doppler lidar system 20 arranged in signal communication with the gravimeter 14. The lidar system 20 is configured to determine a vertical velocity of the aircraft 10 at a predetermined time, with a time signal from the GNSS receiver 18 used to operatively synchronise both the gravimeter 14 and lidar system 20 measurements. In this manner, a gravitational acceleration measurement of the gravimeter 14 is differentially isolable from a kinematic acceleration derivable from the synchronous lidar measurement.

An optomechanical inertial reference mirror combines an optomechanical resonator with a reflector that serves as an inertial reference for an atom interferometer. The optomechanical resonator is optically monitored to obtain a first inertial measurement of the reflector that features high bandwidth and high dynamic range. The atom interferometer generates a second inertial measurement of the reflector that features high accuracy and stability. The second inertial measurement corrects for drift of the first inertial measurement, thereby resulting in a single inertial measurement of the reflector having high bandwidth, high dynamic range, excellent long-term stability, and high accuracy. The reflector may be bonded to the resonator, or formed directly onto a test mass of the resonator. With a volume of less than one cubic centimeter, the optomechanical inertial reference mirror is particularly advantageous for portable atomic-based sensors and systems.

An optomechanical inertial reference mirror combines an optomechanical resonator with a reflector that serves as an inertial reference for an atom interferometer. The optomechanical resonator is optically monitored to obtain a first inertial measurement of the reflector that features high bandwidth and high dynamic range. The atom interferometer generates a second inertial measurement of the reflector that features high accuracy and stability. The second inertial measurement corrects for drift of the first inertial measurement, thereby resulting in a single inertial measurement of the reflector having high bandwidth, high dynamic range, excellent long-term stability, and high accuracy. The reflector may be bonded to the resonator, or formed directly onto a test mass of the resonator. With a volume of less than one cubic centimeter, the optomechanical inertial reference mirror is particularly advantageous for portable atomic-based sensors and systems.

The present invention discloses a MEMS gravimeter comprising: a spring-mass system, a displacement sensing structure, a displacement detecting circuit, a cavity body and a level adjustment base; the spring-mass system is disposed inside the cavity body and includes: a negative-stiffness spring, a positive-stiffness spring, a proof mass and an outer frame; the proof mass is connected to the outer frame by the negative-stiffness spring and the positive-stiffness spring, the negative-stiffness spring and the positive-stiffness spring are symmetrically disposed with respect to the proof mass, and the outer frame is fixedly connected to the cavity body; the displacement sensing structure is located on a surface of the proof mass, and the displacement detecting circuit is configured to detect a displacement signal from the displacement sensing structure; the spring-mass system realizes reduction in resonant frequency by matching of the positive and negative stiffness springs; and change in gravitational acceleration is detected by detecting a displacement of the proof mass. The MEMS gravimeter has high stability, small size and light weight, and thus can effectively reduce the production cost as well as the development difficulty of the signal detection unit and stable platform.

The present invention discloses a MEMS gravimeter comprising: a spring-mass system, a displacement sensing structure, a displacement detecting circuit, a cavity body and a level adjustment base; the spring-mass system is disposed inside the cavity body and includes: a negative-stiffness spring, a positive-stiffness spring, a proof mass and an outer frame; the proof mass is connected to the outer frame by the negative-stiffness spring and the positive-stiffness spring, the negative-stiffness spring and the positive-stiffness spring are symmetrically disposed with respect to the proof mass, and the outer frame is fixedly connected to the cavity body; the displacement sensing structure is located on a surface of the proof mass, and the displacement detecting circuit is configured to detect a displacement signal from the displacement sensing structure; the spring-mass system realizes reduction in resonant frequency by matching of the positive and negative stiffness springs; and change in gravitational acceleration is detected by detecting a displacement of the proof mass. The MEMS gravimeter has high stability, small size and light weight, and thus can effectively reduce the production cost as well as the development difficulty of the signal detection unit and stable platform.

Disclosed is a detector system for detecting underground anomalies comprising a detector device which includes a fluid chamber which is sealed; a float including a target, positioned within the fluid chamber; and a shielded phase shift proximity sensor configured to detect a distance between the target and proximity sensor, wherein a presence of an underground anomaly is determined based on the detected distance.

Disclosed is a detector system for detecting underground anomalies comprising a detector device which includes a fluid chamber which is sealed; a float including a target, positioned within the fluid chamber; and a shielded phase shift proximity sensor configured to detect a distance between the target and proximity sensor, wherein a presence of an underground anomaly is determined based on the detected distance.

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). Thus, each permanent seafloor (120, 121) sensor provide an output that is corrected for drift at any time between calibration surveys. The system may be used for permanent monitoring of a seafloor.

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). Thus, each permanent seafloor (120, 121) sensor provide an output that is corrected for drift at any time between calibration surveys. The system may be used for permanent monitoring of a seafloor.

Example gravity gradiometers are described that utilize high precision resonant optical cavities to measure changes in gravitational forces at high sensitivities. In one example, a sensing system includes a gravity gradiometer and a controller. The gravity gradiometer includes a first mirror and a second mirror arranged to form an optical cavity having an optical axis. The controller is configured to detect, responsive to displacement of at least one of the first mirror and the second mirror along the optical axis, a change in gravity gradient.