GB2628338A

GB2628338A - Submersible devices and associated apparatus

Info

Publication number: GB2628338A
Application number: GB2303778.1A
Authority: GB
Inventors: M Gillott Graham
Original assignee: Talaria Tech Ltd
Current assignee: Talaria Tech Ltd
Priority date: 2023-03-15
Filing date: 2023-03-15
Publication date: 2024-09-25
Also published as: WO2024189344A1; GB202303778D0

Abstract

A submergible device for collecting data relating to geological characteristics of an area of a bed of a body of water comprises a housing, a front end, sensors e.g. Raman spectrometer for collecting geophysical data, a ground-engagement release mechanism, a buoyancy device and a propulsion system e.g. propellor. The propulsion system has a steering system e.g. fins, flaps, ducts. The device is semi-autonomous having control electronics for controlling a dive of the device down to and into the seabed, for embedding the front end of the device at least partially into the bed, using the propulsion system and the steering system to target an area of impact. Control electronics also operate the ground-engagement release mechanism to release the embedded front end from the bed. The propulsion system and/or the buoyancy device are operated for recovering or refloating the device to the water’s surface. The device may include a vibration actuator for shaking the device free and apertures in the nose-cone for releasing gas.

Description

Submersible devices and associated apparatus The present invention relates to a submersible device for data acquisition in respect of seabed rock properties.

One area of technology where the present invention would be useful is in surveying locations for windfarms. Wndfarms are an important part of the global transition away from the reliance on fossil fuels for energy demands. Offshore Installations have commonly been at relatively costal locations due to the easier access, and commonly less deep water, than open water locations. However, as the number of windfarm installations at sea increase, offshore wind companies must push further out to sea as the easier costal installation locations become occupied. Commonly this involves installing larger turbines in deeper water and more challenging ground and sea conditions, which all can lead to significantly increased costs. However, there is an ongoing desire to reduce costs to ensure that the overall energy production can maintain cost effectiveness.

When installing a windfarm at sea, the engineers must have a detailed understanding of the seabed to ensure that any foundation or anchor is appropriately able to be fixed to the seabed. Current approaches for surveying a deepwater seabed, for example below 20m, however, are generally not a cost-effective way of acquiring the required data, especially if physical sampling is to be avoided. For example, typical known approaches use cone penetration tests where two or more sensor assemblies (the cones being the drilling tip of the assemblies) are hammered into the seabed, which sensor assemblies can detect seismic, slope, pressure and strain readings in the rock in response to seismic waves created by ground hammers of a device dropped onto the seabed, the data being fed up an umbilical from the device on the seabed to a support ship on the surface. However, for such tests, the readings are generally only 1 dimensional and many samples are needed to generate pseudo 3D section through the bedrock. As such the ship and device, and sensor assemblies will need to be in a given location for a long period of time. Furthermore, the support ship needs to be of a substantial size to operate and move the device on the seabed, as that device typically is the device to hammer the sensor assemblies into the seabed. Thus, the costs with such an arrangement will be very high -the rental cost of such ships can be in the order of £100,000 per day! Other at-sea installations can have similar issues with the cost of the surveys required prior to designing and installing the seabed interface (foundation or anchor). Due to these high costs, both in terms of time and money, geophysical seabed surveys are not generally done in engineering applications, unless the overall project cost can justify them, such as with windfarm projects at sea.

The present invention thus seeks to provide a novel approach for 1D, 2D and 3D surveying of seabed rock properties in which the costs -time or money -can be substantially reduced to allow application of the technology not just for such windfarm projects, but for other sea (or lake) installations.

In particular, a semi-autonomous sensor delivery system would be of particular benefit to many industries if the costs of use thereof compare favourably versus existing systems.

The device and methods of the present are not just for seabed model development with respect to windfarm installations. Instead the present invention can be useful for any engineering project which needs seabed models prior to installing ground interfaces on the seabed. The data on the seabed geology will be of benefit for the designers of those interfaces, and by the present invention seeking to significantly reduce the requirements for direct physical measurements, digging and sampling, the present invention may allow engineering companies to reduce costs, improve time to completion performance and even expand upon, or speed up, the identification of installation opportunities faster. By helping to identify suitable seabed conditions for at-sea engineering installations both faster and more cost effectively, while still, or better, understanding a chosen seabed location's bedrock properties, or geology, the present invention can also allow appropriate foundation or anchor designs for the given conditions to be designed sooner, or more accurately, and thus potentially reduce their overall size (and thus cost and time for installation) and potentially also to reduce their environmental impact. If better data can be obtained faster, there can be a faster deployment of installations, which in turn, for energy companies, can better enable the desired energy transition from fossil fuels to alternative energies, such as windfarms. However, the present invention can also have application and benefits in other engineering industries due to the speed of deployment, the simplicity of deployment, and the reduced cost of deployment compared to water surface driven equipment such as cone penetration tests.

According to the present invention there is provided a submergible device for collecting data relating to geological characteristics of an area of a bed of a body of water, the device comprising: a housing; a front end; sensors for collecting geophysical data, or response data representing geophysical data; a ground-engagement release mechanism; a buoyancy device; and a propulsion system for powering the device through the water, the propulsion system having associated therewith a steering system; wherein the device is semi-autonomous by further comprising: a) control electronics for controlling a dive of the device down to and into the bed, for embedding the front end of the device at least partially into the bed, using the propulsion system and the steering system to target an area of impact; and b) control electronics for i) operating the ground-engagement release mechanism to subsequently release the embedded front end from the bed and ii) operating the propulsion system and/or the buoyancy device for recovering or refloating the device to the water's surface.

In some embodiments the same control electronics perform both a) the control of the dive and b) the operation of the ground-engagement release mechanism and the recovery or refloating of the device.

The present invention thus provides a semi-autonomous, submergible, geophysical data collection device. The device can be used to self-dive to the bed of the body of water for embedding itself in the bed, and then release itself and resurface for subsequent recovery at the surface. This differs from the prior art which instead either needs to be connected to the surface vessel for embedding itself in the bed of the body of water-for example by a hammering process from the surface through a connecting rod, or needs merely to sit on the bed, rather than be embedded into the bed, whereby the recoverable data of the geology of the bed is potentially inferior.

In some embodiments the device comprises one or more ultrasonic transducer for communication with a vessel at the surface.

In some embodiments the device comprises GPS circuitry for determining its position at the surface.

In some embodiments the device comprises an RF signal generator to generate an RF signal at the surface of the water. This can be used to help a vessel locate the device.

In some embodiments the housing and/or the front end has a hydrophobic coating on its outer surface. A hydrophobic coating allows the device to pass faster through the water for a given propulsional force as it reduces friction from the water.

In some embodiments the steering system utilises any one or more of vectoring the propulsion force from the propulsion system, lateral thrust from ducts, aerofoils, fins, flaps or actuated ducts. With these the steering system can provide a degree of lateral control during the descent of the device to the bed, thus allowing the device to compensate (or largely compensate), for water currents during the descent to the bed.

In some embodiments the device is no more than 500mm long during the descent.

In some embodiments the housing has an external maximum width of no more than 300mm, and more preferably no more than 150mm. Preferably, the external width is the external diameter.

In some embodiments the propulsion system comprises a propeller. Preferably the propeller uses an induction rotor to isolate the electronics from the water. In some embodiments the propulsion system has at least two propellers. In some embodiments they counter-rotate. In some embodiments they are co-axial. In some embodiments the steering system redirects the waterflow from the propellers to provide lateral propulsion forces in addition longitudinal propulsion forces -ideally for a straight descent the longitudinal propulsion forces are vertical. However, where there is a water current to compensate for, the longitudinal propulsion forces (parallel to a central axis of the device) may be slightly off-vertical -but typically no more than 15 degrees off vertical through the majority of the descent.

In some embodiments the device is fitted with a compressed gas canister or storage tank. This may be a replaceable canister, with a bayonet or screw thread fitting, or a quick release press fitting. This can be useful as it may allow rapid redeployment of the device upon recovery if any battery for the control electronics, sensors and propulsion system can last for multiple deployments, and if the buoyancy device (if gas powered) can revert to an initial condition for redeployment of the device. The compressed gas (usually air or carbon dioxide) may be for deploying the buoyancy device and/or for providing compressed gas venting at the front end of the device during the descent. For the latter function, the device comprises apertures in the front end -or in a nose cone at or near the front end, that are selectively connectable to a gas supply that can be selectively released from the compressed gas canister or storage tank -for example by the or one of the control systems. Compressed gas venting at the front of a propelled device in water (and to a lesser extent to the sides of a device, can reduce the frictional forces experienced by the device from the water during that motion, thus allowing a more rapid descent of the device through the water for the same propulsional forces.

In some embodiments the device comprises a battery for the control electronics and/or sensors and/or propulsion system. The battery may be replaceable or rechargeable -for example via inductive loop charging.

In some embodiments the device is fitted with one or more hydrophone. Typically these are provided in the sidewall of the housing. For example, four hydrophones may be provided, equally spaced around the sidewall of the housing.

In some embodiments the device is fitted with one or more translational and rotational sensors -for detecting the full wave field of sensor readings in multiple directions preferably 360 degrees around a longitudinal axis of the device.

In some embodiments the device also comprises one or more sensor for detecting the device's orientation in the water to allow it to try to compensate for any rotation of itself in the water, be that rolling, yawing or pitching. This may be controlled by controlling the propulsion system and the steering system -for example controlling the relative speeds of the two or more propellers, where two or more propellers are used, or controlling the actuated ducts, aerofoils, fins or flaps, when they are provided.

In some embodiments the buoyancy device comprises an inflatable balloon -for inflating with gas from the compressed gas canister or storage tank. In some embodiments the buoyancy device has its own gas supply, different to a gas supply for any compressed gas venting at the front end of the device. More typically, however, a common gas supply is used, and piping and control valves are provided for each from that common gas supply.

In some embodiments the device has a deployment weight of less than 2kg, and more preferably of about or less than 1kg.

In some embodiments the device has a negative buoyancy so that it sinks in fresh water. Preferably it also sinks in seawater. A preferred average density of the device is greater than 1.029 g/cm3, and more preferably greater than 1.05g/cm3. Preferably the average density is less than 1.5g/cm3.

In some embodiments the device comprises a clock to apply time stamps for the recorded data.

In some embodiments the device comprises one or more probe extending from the front end for penetrating deeper into the bed than the front end. The probe may be a metal or a non-metal probe. For example it may be a laser probe for chemical analysis of the bed -or the underlying structure thereof. For example the probe may comprise a Raman spectrometer. In some embodiments the device comprises more than one metal probe, for example two or three or more metal probes, extending from the front end for penetrating deeper into the bed than the front end. The or each probe may include an electrical probe for measuring characteristics of the bed, for example electrical responses of the bed -or the underlying structure thereof. In some embodiments the or each probe may include a thermal probe for measuring thermal properties of the bed-or the underlying structure thereof.

In some embodiments the device comprises electrical sensors attached to the device sides or rear housing.

The electrical sensors may be conductivity and/or temperature sensors for making appropriate measurements to measure the salinity and temperature of the water as the device descends to the seabed and ascends to the surface.

Typically the control systems comprise a processor, a memory, interfaces for the sensors, and software to perform the operational control of the device and the data collection.

In some embodiments the device comprises one or more vibration actuator. The vibration actuator(s) may be to trigger a response from the surrounding area of the bed, for enabling collection of data by relevant sensors of the device. The vibration actuator(s) may alternatively (or additionally) be for shaking the device free from the bed prior to ascent thereof to the surface. In some embodiments the shaking may be operated in addition to generating a compressed airflow through the apertures in the front end, better to assist with freeing the device from the bed. If operated in conjunction with a reverse thrust from the propulsion system and an activation or inflation of the buoyancy device, the device should free itself from the seabed every time.

In a preferred implementation of the present invention, a plurality of such devices are deployed to deploy a sensor array to the seabed for undertaking ground surveys over a wider area -using the multiple devices to acquire data on the bed conditions in more than one area across the wider area. This data can then be used by engineers when designing seabed foundations or seabed anchors over the wider area, for example foundations for multiple wind turbines of a windfarm, or multiple anchors for a single floating turbine, but alternatively also for other engineering projects in sea or lake applications. The present invention thus also provides a kit of parts comprising a plurality of devices as defined above, and a streamer for towing behind a vessel for emitting a seismic energy signal towards the seabed.

Typically each device is utilised for a single, unique area of the bed, although overlap between areas of bed assigned to each device of the plurality of such devices is also possible. It is also possible to use the device to deploy into multiple areas of the bed before collection on the vessel. Usually, however, a recharge after refloat, or a recharge of the battery, is necessary between deployments to the bed.

The multiple devices (or multiple deployments of the same device) collectively collect a wide area dataset for the overall area of bed for analysis by a subsequent system -after collection(s) of the device(s) and download(s) of the data.

Typically the present invention will be used at sea for surveying water at a depth greater than 20m, and up to 300m, although shallower or deeper water, or freshwater applications, are also envisioned.

The key advantages of the present invention are the capability to a) Deploy and recover easily from virtually any size of vessel without specialised handling equipment.

b) Speed down through a vertical water column at speed and maintain its vertical trajectory in the presence of currents so placing itself on the seabed at a point generally coincident in the XY plane with the surface release point from the vessel.

c) Securely couple to the seabed by embedding the front end into the seabed, potentially measuring penetration data on impact (e.g. return forces and depth of impact, so producing in effect mini-CPT measurements.

d) Use a range of sensors to detect data about the bed, which sensors may measure or detect data representative of any one or more of a) seismic responses (e.g. in response to a seismic energy signal from a streamer towed by a boat or ship at the water's surface), b) electric response or activity, c) seismoelectric response or activity, d) geothermal activity, e) thermal response or conductivity, or thermal activity, 0 force response, or movement activity, g) temperature, h) water salinity, j) geochemical information, for example a Raman spectrometer, or j) frictional response.

e) Extract itself from the seabed and return to the surface on command leaving no deployment components behind.

f) Potentially to take CTD profile measurements for water column velocity profiles on deployment and recovery; and g) Potentially to maintain accurate micro-second time stamps of the recorded data.

A preferred set of sensors would include one or various advanced seismic sensors and interfaces for spectrometers, electrical probes and thermal conductivity probes. In a preferred configuration the housing comprises an internal space that can be rendered watertight. The internal space may be adaptable so that it can contain a variety (or specifically chosen set) of sensors and/or control electronics, for carrying out desired sensor readings and control of the other systems of the device.

In particular, the present invention aims to be compact, comparatively inexpensive to build versus existing deep sea sensor assemblies, and likewise comparatively inexpensive to maintain and use in the field. It is also simpler to air-freight them to anywhere in the world in bulk at short notice due to their small size compared to the prior art sensor assemblies and the associated device on the seabed for deployment and use thereof.

In some embodiments, the application of use can include any one or more of the following: * Detection of anisotropic 3D shear profiles.

* Multicomponent active and passive seismic imaging.

* Seabed chemical and gas flux detection and testing.

* Thermal conduction measurements.

* Electrical measurements to derive porosity and permeability measurements for enhanced thermal property derivation and other physical attributes of the seabed and underlying structure thereof * Near seabed CPT response for trenching applications.

* Passive Acoustic Monitoring for marine fauna monitoring.

The present invention can help enable seabed surveys of various descriptions, such as those above, to become more affordable in terms of time and cost, and these can include applications in oceanography, oil and gas exploration, asset monitoring, renewables emplacement, de-risking and seabed engineering, for each of which advance knowledge of the geology of the bed of the body of water is beneficial.

The present invention also provides a method of surveying an area of a bed of a body of water, for determining geological characteristics thereof, comprising providing a submergible device for collecting data relating to geological characteristics of the area of the bed, the device comprising: a housing; a front end; sensors for collecting geophysical data, or response data representing geophysical data; a ground-engagement release mechanism; a buoyancy device; a propulsion system for powering the device through the water, the propulsion system having associated therewith a steering system; control electronics for controlling a dive of the device down to and into the bed,; and control electronics for operating the ground-engagement release mechanism, the propulsion system and the buoyancy device; the method comprising: launching the device from a vessel at a surface of the body of water; using the propulsion system and the steering system to dive the device down to and into the bed of the body of water, embedding the front end of the device at least partially into a target area of impact in the area of the bed; collecting data using the sensors; subsequently releasing the embedded front end from the bed by operating at least one of the ground-engagement release mechanism, the propulsion system and the buoyancy device; and recovering or refloating the device to the water's surface by operating the propulsion system and/or the buoyancy device.

In some embodiments the device is semi-autonomous by performing the dive, the data collection, the release from the bed and the recovery or refloat of the device to the water's surface without user control of the systems on the device.

In some embodiments the device may have communication means for communication with the surface so that an instruction to recover can be transmitted to the device, whereupon the device can commence the steps of releasing from the bed and the recovery or refloat of the device to the water's surface without additional user input. In some embodiments the device can use a control routine to determine whether it is ready to return to the surface before commencing these steps -for example if data is still being captured (or if only repeating data is being captured -i,e, no new data).

The device used in the method is preferably the device of the first aspect of the present invention.

These and other features of the present invention will now be discussed in further detail, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 shows an initiation of a device deployment and descent to a seabed from a surface vessel (usually a boat or a ship); Figure 2 shows a powered descent trajectory controlled by the device to maintain a vertical trajectory from a point of deployment; Figure 3 shows the vessel communicating with the device via, for example, ultrasonic transducers, and instructing the device to return to the surface for example when a survey is complete; Figure 4 shows the device utilising one or more of potentially four methods to extract itself from the seabed prior to its ascent to the surface; Figure 5 shows the ascent to the surface, and a transmission of a locator signal, for example by low bandwidth RF communications, to enable recovery, as when it reaches the surface it may not be in the position where it was dropped. This may be signal to indicate its position (e.g. via GPS) to the vessel, or simply a locator signal; Figures 6 to 8 show a further embodiment of submersible device or device in which two propeller blade sets are provided for controlling and powering the descent of the device to the seabed while maintaining the main body of the device in a fixed orientation relative to the water; Figures 9 and 10 show modified versions of the device of Figures 6 to 8; and Figure 11 schematically shows certain internal components of the device of a preferred embodiment.

Referring first to Figure 1, there is shown a vessel 10 and a submersible device 12 that has been launched off the back of the vessel 10 at a first position p' at sea. This initiation of a deployment and descent of the device 12 to a seabed 14 from the surface vessel 10 (usually a boat or a ship) can be by dropping the device 12 over the side, front or back of the vessel 10. The first position p' can be directly above an aim point p for where the device 12 is intended to be deployed for recording seabed condition data at that aim point p. If the case of deploying multiple devices, multiple aim points will exist -for example in an array across a designated area of seabed 14.

Figure 2 then shows a target descent trajectory 40 to the aim point p -along which the device 12 is intended to drop (by way of a powered drop) through the water with the intention of hitting the aim point p. The descent need not exactly follow this trajectory 40. As shown, there can be currents 18 that can cause drift of the device 12 away from the trajectory 40, as shown by the off-target devices 12' in Figure 2. However, in a preferred device 12, the device 12 can have onboard INS controls and steering actuators to create counter forces 16 from the off-target device 12' to bring the off-target device 12' back to the target trajectory 40. In this embodiment the target trajectory 40 is a vertical trajectory from the point of deployment p'.

In preferred configurations the accuracy of the descent trajectory is intended to be within lm at the seabed in water with a current not exceeding 4 knots, and more preferably this is 0.5m or better. With directional control of propeller propulsion, using, for example, actuated ducts or aerofoils or fins, for example at the back of the device, this is readily achievable over a 20 to 300m dive.

As shown in Figure 2, once the device 12 reaches the seabed 14, it can embed itself into the seabed. For this purpose the device targets a final descent speed of at least 10m/s, Further, it is desirable for the descent to be rapid to minimise the effect of water currents. Ideally the descent should be no more than 30 seconds for a 100m dive.

As shown, the point of impact/embedment is ideally at the aim point p, directly below the position of surface release p'.

Once in position, the device 12 can conduct the required surveying activity, sensing conditions of the seabed, or detecting reference data relating to the geology of the seabed (e.g. response signals) for later analysis.

Figure 3 shows the vessel 10 communicating with the device 12 on the seabed 14 via, for example, ultrasonic transducers on the vessel 10 and the device 12, which each generate an ultrasonic output 24, 26. In this example, the vessel 10 has a GPS positioning system 20 above the surface of the water and an ultrasonic transducer 22 below the surface of the water for generating its ultrasonic output 24 for communications with the device 12 at the seabed 14. The ultrasonic communication may transmit collected data, but more typically the device 12 has a memory for storing the collected data, and instead the ultrasonic transducers are for issuing command prompts or acknowledgement prompts between the vessel 10 and the device 12 as there can be data losses in a transmission between the device 12 and the vessel 10 at the depths at which the devices 12 usually will operate. For example, the transmission 24 may be from the vessel 10 to the device 12 to instruct the device 12 to return to the surface for example when a survey is complete. The transmission from the device 12 to the vessel 10 may then be an acknowledgement of the order, or a request to verify the instruction, or a response to indicate the survey is ongoing.

In some embodiments the device provides no reply, or simply provides a signal to the vessel to indicate it is about to ascend (or that it is ascending or that it has ascended).

Referring next to Figure 4 there is shown a vibration 28 of the nose or cone 42 of the device 12 as may be used to vibrate or shake the device 12 for loosening it from the seabed 14. This may be done before the device can ascend to the surface. This can be one of potentially four methods used by the device 12 to extract itself from the seabed 14 prior to its ascent to the surface.

A second possible method as shown in Figure 4 is for the device 12 to use compressed gas venting 44 at the nose or cone 42 -for example out through a series of apertures 46 in the nose or cone 42 -to aid extraction of the device 12 from the seabed 14. Typically the gas is compressed air or compressed nitrogen.

A third possible method as shown in Figure 4 is provided by a propeller 32, or some other thrust generating mechanism, provided on the device 12 -for example at or near a tail end of the device. With this propeller or thrust generating mechanism, such as a jet/water thruster, a reverse thrust can be generated to pull the device 12 out of and away from the seabed 14. This may, for example, be a reverse operation of the same mechanism used to power the device 12 towards the seabed during the initial deployment of the device 12 to the seabed 14.

A fourth possible method as shown in Figure 4 is for the device 12 to be provided with an integrated mini lift-bag or buoyancy aid 30 that can be activated or inflated on or in or above the device 12. The buoyancy of the device -now including the activated or inflated buoyancy aid can thus then create an additional lifting force which may instead or additionally be used to dislodge the device 12 from the seabed 14 and to thereafter allow it to rise to the surface of the water.

Referring next to Figure 5 there is shown a possible ascent 36 of the device 12 to the surface, and a transmission of a locator signal 34, for example by low bandwidth RF communications, to enable recovery, as when it reaches the surface it may not be in the position where it was dropped. This may be signal to indicate its position (e.g. via GPS) to the vessel 10, or simply a locator signal. In some embodiments there may be active control of the ascent to keep the device 12 on or near the previous descent trajectory 40 to allow the device to be quickly recovered by the vessel. However, in some embodiments there may not be active lateral control on ascent so the currents 18 (see Figure 2) will draw the device 12 off that line 40.

When the surface is reached, and if provided, as soon as a GPS fix is received by a GPS module on the device, the locator signal 34 may be triggered, the signal then typically including the above-discussed location position -the device transmitting its position via low frequency RF transmitter, for example, again to allow rapid recovery.

The recovery may be by any vessel 10. It doesn't have to be the same vessel that deployed the device 12.

The present invention thus has the advantage of being semi-autonomous in that it is dropped into the water and guides itself to the seabed. It is a simple "drop and pop" deployment and recovery system.

Referring next to figures 6 to 10, three further possible external designs for the device 12 are shown.

In Figures 6 to 8, the device 12 can be seen to have a dual propeller 32 at its tail (upper) end, which propeller 32 has first and second blade sets 48, 50 that counter-rotate relative to one another. They have reversed pitches on the blades thereof. Through counter-rotation, a main body 38 of the device 12, including the nose or cone 42 and a tail 52, does not rotate relative to the body of water during the ascent or descent of the device (or if it does rotate relative to the water, it does not rotate rapidly).

Referring next to Figures 9 and 10 two further versions of device 12 are shown. In these embodiments, the propeller 32 is again present but the propeller is housed within a flow-guide casing or duct 58. Figure 10 then differs from that of Figure 9 by the provision of downwardly extending, smaller, side probes 60, such as electrical or thermal probes for example for generating and measuring electrical responses of the bed -or the underlying structure thereof, or for measuring thermal properties of the bed-or the underlying structure thereof, and a downwardly extending larger central probe 62 at the free end of the nose or cone 42 -for example a probe with a laser probe or geochemical sensor incorporated therein, such as a Raman spectrometer.

In each of the embodiments in Figures 6 to 10, an upper port 56 is provided at the tail end 52. This upper port can accommodate a buoyancy aid 30 prior to its deployment (see Figures 4 and 5). Referring also to Figures 8, 9 and 10, a mounting flange 80 is also shown. This can be provided to accommodate a removable gas canister 78 (see Figure 11) for inflating the buoyancy aid (not visible in these figures as it is not yet inflated, but it could be an inflation of a void with a displaceable roof, for example).

Referring finally to Figure 11, a possible internal layout -or a schematic illustration of the internal components of the device 12 -is shown. As can be seen, at the tail end 52 of the device 12 there is the upper port 56 which can accommodate a non-inflated balloon 76, or some other such buoyancy aid, for example to provide the mini lift bag or buoyancy aid 30 as shown in Figure 4, once inflated, or such like.

Figure 11 also shows a powered descent drive system 74 for driving the propulsion system -for example the propellers 32 in the preceding figures. These may be connected thereto by induction rotors so that the internal electrics are isolated from the seawater. This thus provides the motors for driving the propellers 32.

There is then a set of electronics 64 for controlling the various parts of the device, and for recording sensed data, and potentially for processing that data. These electronics 64 will include a CPU, memory and connections to the various sensors and other components of the device.

The sensors of this example include multiple hydrophones 66 -two are shown as an example, and a rotational sensor 68. These or other sensors can be to provide various functions for the device 12, as discussed above and below. For example, the device can be a semi-autonomous, self-contained, data acquisition system (SADAS) for multiple data type acquisition including: * 1D, 2D and/or 3D seismic data acquisition for P-wave, S wave and Surface wave.

* Spectral analyses of chemical fluid and gas measurement and dissolved gas.

* Seismoelectric measurement using an electrical probe.

* Thermal conductivity measurements of the seabed.

* Temperature and salinity measurements of the surrounding water column while in transit and/or in-situ once embedded in the seabed.

* Dynamic seabed impact measurements for determining mechanical properties of the seabed * A GPS sensor/receiver * An RF sensor/receiver and or transmitter * An acoustic and/or optical transceiver.

* Vibration sensors and/or generators.

The other components of the device may include any one or more of: a. an RF long range transmitter, potentially connected to the GPS sensor/receiver for position confirmation prior to sub-sea deployment and for enabling location detection after ascent for assisting with device recovery by the vessel 10 -e.g. by transmitting its GPS identified position.

b. An acoustic transceiver to receive command instructions (for example for over-ride or recommendation purposes) and to transmit a beacon for location fixing, or for later recovery.

c. A system for powered descent and enforced coupling (impact landing and embedment) of the device 12 with the seabed, such as i. An active propeller / thrusters for descent (and possibly the ascent).

ii. Ducted thrust with one or more actuator or flow deflector/aerofoil/fin or flap to allow lateral control on descent (and optionally on ascent), for example to counteract the effect of currents on the device during the descent/ascent.

iii. Aeration of compressed gas (usually air or nitrogen), for example stored in the nose cone, or in a gas canister/storage vessel at the back, or elsewhere in or on the device) for reducing buoyancy by aerating the surrounding water, and by reducing surface friction round the device relative to the water, and thus enabling a faster descent of the device at depth.

The device may even be provided with an external hydrophobic coating on one or more surface of the device 12 to maximise its velocity on impact at the seabed. The hydrophobic coating also can reduce friction within the water. This can additionally help ensure a correct deployment of the device into (rather than just onto) the seabed -i.e. for efficiently coupling the device to the material of the seabed. It ideally embeds deeply into the seabed, for example to a depth of a front cone of the device, rather than being left to sit just on the upper surface of the seabed, as this then better couples the device, and thus the sensors, to the material of the seabed, thus enabling better data about the geophysics and geology of the seabed to be captured.

The components of the device also includes any one or more of: d. a system for assisted decoupling of the device 12 from the seabed 14, such as: i. A seabed aeration system (potentially the same system as used in accelerating the descent of the device to the seabed, but instead to assist with decoupling of the device from the seabed, as shown in Figure 4) Vibrating actuators to shake device free from the seabed 14.

e. A system for powered ascent and recovery of the device 12, such as: iii. A compact lift float or buoyancy aid that may be inflated by compressed air, and control circuity for that decompression of stored air (e.g. in the nose cone, or the compressed gas canister/storage area at the rear of the device); iv. A propeller and/or thruster that operates in a reversed mode for assisted extraction and ascent from the seabed.

f. A multifunctional sensor space adapted for accommodating the various sensors and circuitry therefor for sampling and retention of differing data types (e.g. for providing one or more of the detection functions as above), with pre-determined payload capabilities (weights of the sensors or more likely volume and weight of the sensors) to ensure appropriate device buoyancy and thus intended operability of the descent and recovery mechanisms.

e. A generalised high bandwidth data logging system for any and/or each type of sensor data being collected and one or more sensor database/storage (usually a central storage) which can collect and store the received data from any and/or each type of senor provided, for example for enabling extended seabed-based monitoring for seismic and non-seismic datasets. For example, the sensors and data collection may detect and collect data designed to recover or ascertain accurate shear modulus readings of near seabed, and CPT borehole data upon impact with the seabed, along with data after the impact.

Returning to Figure 11, the device 12 can also be seen to comprise a battery 70 -which in this example is fitted in the nose 42 of the device 12, and a vibration actuator 72 for assisting with the release of the device from the seabed prior to ascent.

The device is usually one of a set of many such devices deployed at a given location at which seabed structure is desired to be surveyed, each spaced apart from one another generally in a grid or net around the site.

The device of the present invention is typically smaller than prior art seabed sensor assemblies -with the main body typically being generally round in section with a diameter less than 300mm and an overall length before the balloon is inflated of less than 500mm. In some embodiments the diameter is about 120mm and the length before balloon deployment is about 200mm. In other embodiments the device before balloon inflation is about 400mm (40cm) and the propellers have an external diameter of about 220mm (22cm). The device 12 is thus a relatively small, sensor laden, semi-autonomous, unit (usually one of a set of units) that can be deployed over the side of a small, nonspecialist vessel. The units descend under power and bury or penetrate themselves in the seabed to ensure good coupling thereto (thus allowing better sensing of the subsea structure).

In use the vessel above will typically tow a small seismic energy source and the sensor arrays in the units detect and record seabed surface and body waves and other information in response to the seismic energy source, thus allowing a series of seabed data to be recorded by the units. Other data can also be collected by the sensors in the device relating to the subsea structure or geology.

Although as little as one unit can be used, an arrangement in which more than 20, or more preferably between 50 and 150 (ideally 100) units can be used to build a detailed picture of the geology, which can even be a 3D image, especially if the seabed is not flat.

The higher the density of units. the higher the spatial resolution. Combining the data from any two or more units already starts to build information about the seabed in a rapid and lower cost manner than that previously achievable, and overlap of the areas of detection can be accommodated by the processing at the surface.

Once the data recording is completed (on command from the vessel, or after a set time period) the units shake or otherwise release themselves out of the seabed, and they then propel or otherwise float themselves to the surface for retrieval, data download and recharge. For that purpose, the battery 70 may be a rechargeable battery and the gas canister or storage area can be replaceable or refillable.

With the present invention, the total survey duration for a single localised installation site can be as!ale as two hours. For a large site, as little as 8-10 days. Further, no specialist vessels are needed to transport the equipment to the survey site. The invention also allows a quick and low-cost mobilization anywhere in the world as it is suitable for both deepwater installations and shallower water installations -usually 20 to 300m depths, although other depths can also be accommodated. This makes the present invention highly beneficial for surveying sites for floating wind turbine applications where the turbines are tethered to the seabed by multiple anchors.

With the present invention -particularly a multiple unit implementation, the present invention enables 3D reflection seismic data to be obtained with or without a combination of a towed mini streamer and the units. Further details in 3D of the subterranean rock properties can be obtained, and in particular the low strain shear modulus of the seabed can be determined across a wide area of the seabed.

It is also possible to take in-situ physical measurements using the probe 62 to calibrate the readings.

The present invention also achieves significant cost savings due to the potential to use a small vessel with minimal back deck space -potentially reducing the rental costs to closer to $6,000 per day per boat, and due to the small nature of the devices, they can have a faster mobilisation to site from equipment arriving at quayside -usually no more than 2 days, with each localised site deployment typically taking 20 minutes to deploy, whereby each survey site may only take around 3 hours to set up and 1 hour to shoot (do the sensing) using a towed mini streamer, and with the option to use a separate small vessel for respective deployment and recovery.

It should also be noted that units can instead be sparsely deployed since surface waves are fully characterized locally using rotational sensors, and they can be as sparse or as dense as a client demands -with the spatial resolution being improved by higher densities. Aliasing is generally not likely to cause restrictions as that can be accounted for by the later processing of the data.

These and other features of the present invention have been described above purely by way of example. Modifications in detail may be made to the invention within the scope of the claims as appended hereto.

Claims

CLAIMS: 1. A submergible device for collecting data relating to geological characteristics of an area of a bed of a body of water, the device comprising: a housing; a front end; sensors for collecting geophysical data, or response data representing geophysical data; a ground-engagement release mechanism; a buoyancy device; and a propulsion system for powering the device through the water, the propulsion system having associated therewith a steering system; wherein the device is semi-autonomous by further comprising: a) control electronics for controlling a dive of the device down to and into the bed, for embedding the front end of the device at least partially into the bed, using the propulsion system and the steering system to target an area of impact; and b) control electronics for i) operating the ground-engagement release mechanism to subsequently release the embedded front end from the bed and ii) operating the propulsion system and/or the buoyancy device for recovering or refloating the device to the water's surface.
2. The device of claim 1, wherein the same control electronics perform both a) the control of the dive and b) the operation of the ground-engagement release mechanism and the recovery or refloating of the device.
3. The device of claim 1 or claim 2, further comprising at least one ultrasonic transducer for communication with a vessel at the surface.
4. The device of any one of the preceding claims, further comprising GPS circuitry for determining its position at the surface.
5. The device of any one of the preceding claims, further comprising an RF signal generator to generate an RF signal at the surface of the water.
6. The device of any one of the preceding claims, wherein the housing and/or the front end has a hydrophobic coating on its outer surface.
7. The device of any one of the preceding claims, wherein the steering system utilises any one or more of vectoring the propulsion force from the propulsion system, lateral thrust from ducts, aerofoils, fins, flaps or actuated ducts.
8. The device of any one of the preceding claims, wherein the device is no more than 500mm long during the descent.
9. The device of any one of the preceding claims, wherein the housing has an external maximum width of no more than 300mm.
10. The device of any one of the preceding claims, wherein the propulsion system comprises a propeller.
11. The device of claim 10, wherein the propulsion system has at least one propeller.
12. The device of claim 11 wherein there are at least two propellers and the at least two propellers counter-rotate.
13. The device of claim 12, wherein the propellers are co-axial.
14. The device of any one of the preceding claims, wherein the steering system redirects waterflow from the propulsion system to provide lateral propulsion forces in addition longitudinal propulsion forces.
15. The device of any one of the preceding claims, further comprising a compressed gas canister or storage tank.
16. The device of any one of the preceding claims, wherein the compressed gas canister or storage tank is a replaceable canister.
17. The device of claim 15 or claim 16, wherein compressed gas in the canister or storage tank is for deploying the buoyancy device.
18. The device of claim 15, claim 16 or claim 17, wherein compressed gas in the canister or storage tank is for providing compressed gas venting at the front end of the device during the descent.
19. The device of any one of the preceding claims, further comprising apertures in the front end or in a nose cone at or near the front end, that are selectively connectable to a gas supply that can selectively release gas therethrough.
20. The device of any one of the preceding claims, further comprising a battery for the control electronics and/or sensors and/or propulsion system.
21. The device of claim 20, wherein the battery is rechargeable.
22. The device of any one of the preceding claims, further comprising one or more hydrophone.
23. The device of any one of the preceding claims, further comprising one or more rotational sensors for detecting sensor readings in multiple directions.
24. The device of any one of the preceding claims, further comprising one or more sensor for detecting the device's orientation in the water.
25. The device of any one of the preceding claims, wherein the buoyancy device comprises an inflatable balloon.
26. The device of any one of the preceding claims, wherein the device has a deployment weight of less than 2kg.
27. The device of any one of the preceding claims, wherein the device has a negative buoyancy so that it sinks in seawater.
28. The device of any one of the preceding claims, further comprising a clock to apply time stamps for the recorded data.
29. The device of any one of the preceding claims, further comprising a probe extending from the front end for penetrating deeper into the bed than the front end.
30. The device of any one of the preceding claims, further comprising a laser probe for chemical analysis of the bed -or the underlying structure thereof.
31. The device of claim 30, wherein the probe is a Raman spectrometer.
32. The device of any one of the preceding claims, further comprising one or more vibration actuator.
33. The device of claim 32, wherein the vibration actuator is for shaking the device free from the bed prior to ascent thereof to the surface.
34. The device of claim 15 or claim 16, wherein compressed gas in the canister or storage tank is for deploying the buoyancy device.
35. The device of any one of the preceding claims, comprising apertures in the front end or in a nose cone at or near the front end, that are selectively connectable to a gas supply that can selectively release gas therethrough to assist with freeing the device from the bed.
36. A method of using the device of any one of the preceding claims, wherein the device is a semi-autonomous, submergible, geophysical data collection device, the device self-diving to the bed of the body of water for embedding itself in the bed, and then later releasing itself and resurfacing for subsequent recovery at the surface.
37. A kit of parts comprising a plurality of devices according to any one of claims 1 to 35, and a streamer for towing behind a vessel for emitting a seismic energy signal towards the seabed.
38. A method of surveying an area of a bed of a body of water, for determining geological characteristics thereof, comprising providing a submergible device for collecting data relating to geological characteristics of the area of the bed, the device comprising: a housing; a front end; sensors for collecting geophysical data, or response data representing geophysical data; a ground-engagement release mechanism; a buoyancy device; a propulsion system for powering the device through the water, the propulsion system having associated therewith a steering system; control electronics for controlling a dive of the device down to and into the bed,; and control electronics for operating the ground-engagement release mechanism, the propulsion system and the buoyancy device; the method comprising: launching the device from a vessel at a surface of the body of water; using the propulsion system and the steering system to dive the device down to and into the bed of the body of water, embedding the front end of the device at least partially into a target area of impact in the area of the bed; collecting data using the sensors; subsequently releasing the embedded front end from the bed by operating at least one of the ground-engagement release mechanism, the propulsion system and the buoyancy device; and recovering or refloating the device to the water's surface by operating the propulsion system and/or the buoyancy device.
39. The method of claim 38, operated semi-autonomously, by the device performing the dive, the data collection, the release from the bed and the recovery or refloat of the device to the water's surface without user control of the systems on the device.
40. The method of claim 38 or claim 39, wherein the device has communication means for communication with the surface so that an instruction to recover can be transmitted to the device.
41. The method of claim 40, wherein upon receipt of the instruction to recover, the device can commence the steps of releasing from the bed and the recovery or refloat of the device to the water's surface without additional user input.
42. The method of claim 40 or claim 41, wherein the device uses a control routine to determine whether it is ready to return to the surface before commencing the steps of releasing from the bed and the recovery or refloat of the device to the water's surface.
43. The method of any one of claims 38 to 42, wherein the device is in accordance with any one of claims 1 to 35.
44. The method of any one of claims 38 to 43, wherein a plurality of the devices are deployed to deploy a sensor array to the bed.
45. The method of claim 44, wherein the method uses a single streamer behind a vessel for triggering seismic reactions from the bed for detection by all the devices.