Abstract: A method of communicating with an underwater vehicle comprising a propulsion system for propelling the vehicle through the water. A series of data sets are encoded and transmitted to the underwater vehicle in a series of signal bursts, and decoded at the underwater vehicle. The propulsion system is operated in a series of thrust pulses separated by drift periods such that the propulsion system operates at a relatively high rate during the thrust pulses and at a relatively low (or zero) rate during the drift periods. The drift periods are timed such that each signal burst arrives at the underwater vehicle during a drift period and not during a thrust pulse. The method may be performed with a single vehicle or a plurality of underwater vehicles. The encoded data signals are broadcast simultaneously to the underwater vehicles in the series of signal bursts.

Abstract: A method of determining the position of an underwater node. The positions of three or more transmitters are determined. Each transmitter transmits at least four pulses, wherein a time difference between each pulse and a previous one of the pulses is proportional to a respective co-ordinate of the position of the transmitter. The pulses are received at the underwater node and decoded by measuring the delays between them, thereby determining the co-ordinates of the transmitters. The range of each transmitter relative to the underwater node is also determined. Finally the position of the underwater node is determined in accordance with the co-ordinates and ranges. Any errors in the measurements of the delays between the pulses only translate into small errors in the determined position because of the proportionality between the delays and the coordinates. Therefore if there is a gradual decrease of signal-to-noise ratio then the accuracy of the position estimate also degrades gradually.

Abstract: A method of determining the position of an underwater node. The positions of three or more transmitters are determined. Each transmitter transmits at least four pulses, wherein a time difference between each pulse and a previous one of the pulses is proportional to a respective co-ordinate of the position of the transmitter. The pulses are received at the underwater node and decoded by measuring the delays between them, thereby determining the co-ordinates of the transmitters. The range of each transmitter relative to the underwater node is also determined. Finally the position of the underwater node is determined in accordance with the co-ordinates and ranges. Any errors in the measurements of the delays between the pulses only translate into small errors in the determined position because of the proportionality between the delays and the coordinates. Therefore if there is a gradual decrease of signal-to-noise ratio then the accuracy of the position estimate also degrades gradually.

Abstract: A method of communicating with an underwater vehicle comprising a propulsion system for propelling the vehicle through the water. A series of data sets are encoded and transmitted to the underwater vehicle in a series of signal bursts, and decoded at the underwater vehicle. The propulsion system is operated in a series of thrust pulses separated by drift periods such that the propulsion system operates at a relatively high rate during the thrust pulses and at a relatively low (or zero) rate during the drift periods. The drift periods are timed such that each signal burst arrives at the underwater vehicle during a drift period and not during a thrust pulse. The method may be performed with a single vehicle or a plurality of underwater vehicles. The encoded data signals are broadcast simultaneously to the underwater vehicles in the series of signal bursts.

Abstract: An annular vehicle having a body which defines a body axis and appears substantially annular when viewed along the body axis. The interior of the annulus defines a duct which is open at both ends. The vehicle includes an electric field (EF) coupled dipole antenna arrangement for electro-magnetic communications, which includes at least one dipole antenna. The vehicle is used as a node in an underwater communications system for communicating with other node(s) using their EF coupled dipole antenna arrangements. The electric field coupled dipole antenna arrangement can provide communications with lower latency than systems employing acoustic communications. The annular body provides good separation for electrodes of the EF coupled dipole antenna arrangement disposed around the body.

Abstract: A method of deploying a device to the seabed with a submersible vehicle, the vehicle having a hull which defines a hull axis and appears substantially annular when viewed along the hull axis. The hull has an interior defining a duct which is open at both ends. The device is mounted to the hull on one or more struts so that it is positioned in line with the duct or at least partially within the duct. The device is transported to the seabed mounted to the hull on the strut(s), water flowing through the duct as it does so. The device is then deployed on the seabed after it has been transported to the seabed by the vehicle.

Abstract: A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. At least part of the outer hull is swept with respect to the hull axis A buoyancy control system may be provided. Various methods of deploying and using the vehicle are described.

Abstract: A seismic sensor node 1 comprising one or more seismic sensors (8,9) and an annular skirt (3) defining an annular axis. The annular skirt (3) has a cutting edge (10) which appears serrated when viewed at a right angle to the annular axis. The skirt (3) also has a series of ribs (15) and channels (11) which terminate at the cutting edge so that the cutting edge has an undulating shape when viewed parallel with the annular axis. The ribbed shape of the skirt (3) makes it particularly resistant to ellipsoid or modal oscillation, so that it can transmit seismic vibrations to the seismic sensor (s) with minimal distortion, attenuation or damping.

Abstract: A seismic sensor node comprising an annular body (2) with an annular cutting edge (3) at one end. One or more seismic sensors (8, 9) are coupled to the annular body (2). The annular body (2) surrounds a duct (5) which is open at either end to permit liquid to flow through the duct, and which increases in cross-sectional area as it extends towards the cutting edge (3). The compression of the seabed material squeezes out water from the material, making it more dense so that it transmit seismic vibrations more efficiently. The shape of the duct (5) also means that the centre of gravity of the node is lower than it would be for a cylindrical node—thus increasing the stability of the node compared with a cylindrical one.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis. A direction of thrust of the first propulsion device can be adjusted independently of the direction of thrust of the second propulsion device and/or a magnitude of thrust of the first propulsion device can be adjusted independently of the magnitude of thrust of the second propulsion device.

Abstract: A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. At least part of the outer hull is swept with respect to the hull axis. A buoyancy control system may be provided. Various methods of deploying and using the vehicle are described.

Abstract: A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. The vehicle further comprising means for rolling the vehicle about the hull axis. A buoyancy control system may be provided, and the outer hull may be swept with respect to the hull axis. Various methods of deploying and using the vehicle are described.

Abstract: A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. At least part of the outer hull is swept with respect to the hull axis A buoyancy control system may be provided. Various methods of deploying and using the vehicle are described.

Abstract: An airborne vehicle having a wing-body which defines a wing-body axis and appears substantially annular when viewed along the wing-body axis, the interior of the annulus defining a duct which is open at both ends. A propulsion system is provided comprising one or more pairs of propulsion devices, each pair comprising a first propulsion device mounted to the wing-body and positioned on a first side of a plane including the wing-body axis, and a second propulsion device mounted to the wing-body and positioned on a second side of the plane including the wing-body axis. A direction of thrust of the first propulsion device can be adjusted independently of the direction of thrust of the second propulsion device and/or a magnitude of thrust of the first propulsion device can be adjusted independently of the magnitude of thrust of the second propulsion device.

Abstract: A submersible vehicle having an outer hull which defines a hull axis and appears substantially annular when viewed along the hull axis, the interior of the annulus defining a duct which is open at both ends so that when the vehicle is submerged in a liquid, the liquid floods the duct. The vehicle further comprising means for rolling the vehicle about the hull axis. A buoyancy control system may be provided, and the outer hull may be swept with respect to the hull axis. Various methods of deploying and using the vehicle are described.