FR3143773A1 - Underwater basement monitoring unit and associated method - Google Patents

Abstract

Underwater basement monitoring unit and associated method The invention relates to a monitoring unit (10) of an underwater subsurface, the monitoring unit (10) being adapted to be placed on a seabed, the monitoring unit (10) comprising at least a sensor (20), preferably at least one geophone or at least one hydrophone (20). The monitoring unit (10) includes a memory and a communications module adapted to communicate wirelessly with a surface unit. The invention further relates to an associated monitoring method. Figure for abstract: Fig 1

Description

Submarine basement monitoring unit and associated method

The present invention relates to a unit for monitoring an underwater subsoil, the monitoring unit being adapted to be deposited on a seabed, the monitoring unit comprising at least one sensor, preferably at least one geophone or at least one hydrophone.

The invention further relates to an associated monitoring method.

Such monitoring makes it possible, for example, to generate an image or profile of a reservoir present in the subsoil of the seabed or to detect the presence or absence in this reservoir of resources such as oil or gas.

To do this, a first possibility consists of deploying one or more acoustic sources, towed by a specialized vessel, and hundreds of receivers mounted, assembled in a network and towed by the same vessel.

The sources generate acoustic waves that propagate in the seabed and are variably reflected by the geophysical structure of the ground beneath the seabed. The reflected waves travel to the receivers that detect them. This then makes it possible to generate an image of the subsoil beneath the seabed, and thus of a possible reservoir.

Another possibility is to place a large number of units on the seabed and generate acoustic waves from the surface, the units being adapted to detect waves reflected by the subsoil of the seabed. Once the measurements have been made, the units are recovered to download the recorded data corresponding to a campaign.

However, such a campaign is particularly costly, as it requires the use of expensive specialist vessels for several months and/or the analysis of a large amount of data.

Additionally, a campaign only allows you to obtain one image at a given time.

To observe the evolution of the reservoir, it is then necessary to carry out a new campaign, therefore to redeploy the sources and receivers towed by the ship or to place new units on the seabed.

Furthermore, to obtain comparable results, it is preferable to re-deposit the units on the seabed in approximately the same locations as before, which is particularly difficult and requires, for example, the use of a specialized remotely controllable underwater vehicle.

This is therefore complex to implement and expensive.

One aim of the invention is to propose a monitoring unit enabling monitoring that is easy to implement and less expensive.

For this purpose, the invention relates to a unit of the aforementioned type, in which the monitoring unit comprises a memory and a communication module adapted to communicate wirelessly with a surface unit.

Such a unit allows communication with the surface without requiring its recovery. Thus, it does not have to be recovered and then redeployed for each data transmission, and in particular for each possible campaign.

The unit according to the invention may further comprise one or more of the following characteristics, considered in isolation or in any technically conceivable combination:

- the communication module is adapted to communicate via water with the surface unit;

- the communication module includes an acoustic modem;

- the monitoring unit comprises a processor configured to manage the acquisition of measurements by the at least one sensor, the recording of the acquired measurements in the memory and the communication by the communication module;

- the processor is configured to trigger the recording of acquired measurements when the acquired measurements exceed a threshold;

- the processor is configured to cause the recording of measurements acquired during a time interval comprising the instant of exceeding the threshold, a first duration before exceeding the threshold and a second duration after exceeding the threshold;

- the processor is configured to receive from the communication module instructions received by the communication module, the processor being configured to execute the instructions; and/or

- the monitoring unit comprises at least one buoy, the buoy being connected to a main body of the monitoring unit by a deployable holding system, the deployable holding system being adapted to be deployed after the monitoring unit receives an acoustic deployment signal.

The invention further relates to monitoring an underwater subsoil of a body of water, comprising the following steps:

- deployment of at least one surveillance unit of the preceding type, the at least one surveillance unit being deposited on a seabed at a respective target location,

- emission of acoustic waves into the body of water by an acoustic source, and

- reception of a wave reflected by at least one monitoring unit.

The method according to the invention may further comprise one or more of the following characteristics, considered in isolation or in any technically conceivable combination:

- the deployment of the at least one surveillance unit comprises the positioning of the corresponding surveillance unit above the respective target location by a lifting device, and the dropping of the surveillance unit; and/or

- a step of recovering the at least one monitoring unit, the at least one monitoring unit comprising at least one buoy, the buoy being connected to a main body of the monitoring unit by a deployable holding system, the deployable holding system being adapted to be deployed after the monitoring unit receives an acoustic deployment signal, the recovery step comprising the emission of an acoustic deployment signal, the deployment of the deployable holding system and the recovery of the monitoring unit by pulling the buoy or the deployable means system.

- the method comprises a step of sending by a surface unit an acoustic wave of collection instruction comprising an instruction, given to at least one monitoring unit, to transmit the recorded acquired measurements, the method comprising a subsequent step of transmission by the communication mode of the at least one given monitoring unit of the recorded acquired measurements; and

- the method comprises a step of sending by a surface unit an acoustic adjustment wave comprising an instruction to adjust at least one parameter of at least one given monitoring unit according to an instruction, the method comprising a subsequent step of adjusting the at least one parameter of the at least one given monitoring unit according to the instruction.

Other aspects and advantages of the invention will appear on reading the following description, given by way of example and with reference to the appended drawings, in which:

there is a three-dimensional schematic view of an exemplary monitoring unit according to an embodiment of the invention, with a release system,

there is a functional schematic view of part of the monitoring unit,

there is a schematic view of an example of a reflected acoustic wave received by the monitoring unit,

there is a schematic view of an example of a deployment step of a monitoring unit according to the invention,

there is a schematic view of an example of a measuring step with a monitoring unit according to the invention,

there is a schematic view of an example of a communication step of monitoring units according to the invention with a surface unit, and

there is a schematic view of successive steps for the recovery of a monitoring unit according to one embodiment of the invention.

An example of a monitoring unit 10 of an underwater subsoil is shown in Figures 1 and 2.

The monitoring unit 10 is adapted to be placed on a seabed.

In the example shown, the monitoring unit 10 comprises, for example, a waterproof housing or enclosure 12.

The housing 12 is adapted to withstand pressures corresponding to the desired seabed depth.

The housing 12 has, for example, a generally cylindrical shape.

In the example shown, the monitoring unit 10 further comprises here a base plate 14 and, here further, a flotation plate 16.

The housing 12 is arranged between the base plate 14 and the flotation plate 16.

The base plate 14 is adapted to rest on the seabed when the monitoring unit is placed thereon.

The base plate 14 is flat here.

The projection of the housing 12 along the axis perpendicular to the base plate 14 is included in the base plate 14.

In particular, the base plate 14 has an area greater than the product of the diameter of the cylinder and the height of the cylinder forming the housing 12.

The base plate 14 in particular prevents the monitoring unit from sinking into the seabed by distributing the weight of the unit over its entire surface.

The flotation plate 16 has buoyancy, so as to exert a force on the monitoring unit 10 in the vertical direction and towards the surface.

Said buoyancy is less than a value such that in the absence of additional force, more particularly for any force less than the force of a current of 4 knots (i.e. approximately 7.4 km/h), the monitoring unit remains on the seabed.

According to the invention, the monitoring unit 10 comprises at least one sensor 18, 20, a memory 22 and a communication module 24.

The monitoring unit further comprises a processor 26.

The monitoring unit further comprises a power source 28.

The at least one sensor is here adapted to measure an acoustic wave, more particularly its amplitude at a given moment, in the environment of the monitoring unit 10.

The at least one sensor here comprises at least one geophone 18 or at least one hydrophone 20. In the example shown, the at least one sensor here comprises at least one geophone 18 and at least one hydrophone 20, more particularly here a geophone 18 and a hydrophone 20.

The geophone 18 is, for example, arranged inside the housing 12.

The geophone 18 is capable of measuring the acoustic waves received in the housing 12.

The hydrophone 20 is capable of measuring any acoustic wave in the water surrounding said hydrophone.

The hydrophone 20 is arranged outside the housing 12.

The memory 22 is suitable for storing data, for example at least 2 megabytes of data.

The memory 22 is arranged inside the housing 12.

The communication module 24 is adapted to communicate wirelessly with a surface unit, more particularly via water.

“Surface unit” means a unit on the surface, for example a boat or a platform, for example floating, or submerged from the surface into water and connected to said surface, for example to a boat.

The communication module 24 comprises, for example, an acoustic modem 30.

The acoustic modem 30 is here arranged outside the housing 12.

The acoustic modem 30 is adapted to transform an electronic signal into an acoustic wave, and here conversely, emitted into the environment, here the water, surrounding the monitoring unit.

More particularly, the acoustic modem 30 is adapted to transform an electronic signal transmitted by the processor 26 via a communication port 32 to the acoustic modem 30 into an acoustic signal emitted in the water surrounding the acoustic modem.

Communication port 32 is, for example, a port for a serial type communication channel, for example according to the RS-232 standard.

The acoustic modem 30 is further capable of converting an acoustic signal received by the acoustic modem into an electronic signal and transmitting it to the processor 26 via the communication port 32.

The processor 26 is configured to manage the acquisition of measurements by the at least one sensor 18, 20, the recording of the acquired measurements in the memory 22 and the communication by the communication module 24.

The processor is here arranged inside the housing 12.

The processor 26 is, for example, connected to a clock 34.

Clock 34 is, for example, an atomic clock.

The clock 34 is arranged inside the housing 12.

The processor 26 is adapted to associate with a measurement of the at least one sensor the time of the measurement according to the clock 34.

The measurements are here acquired by the at least one sensor 18, 20 according to an acquisition frequency and an acquisition resolution, which are, for example, adjustable.

The acquisition frequency is, for example, between 50 Hz and 500 Hz.

In an advantageous embodiment, the processor 26 is configured to trigger the recording in the memory 22 of the measurements acquired by at least one of the at least one sensor 18, 20, when the measurements acquired by one of the at least one sensor 18, 20 exceed a threshold As, here for example the measurements acquired by the hydrophone 20.

Additionally or alternatively, the processor 26 is configured to trigger recording in the memory 22 when the measurements acquired by the geophone 18 exceed a threshold As.

In a particular embodiment, the monitoring unit 10 comprises a parameter corresponding to the sensor whose acquired measurements are considered to determine the exceeding of the threshold As. The parameter is likely to be modified, for example between the geophone 18 and the hydrophone 20.

The measurements recorded during the recording are, for example, all of the measurements acquired by the at least one sensor 18, 20, here by the geophone 18 and the hydrophone 20. Alternatively, only the measurements acquired by the sensor determining the exceeding of the threshold are, for example, recorded.

Here we define the moment of exceeding the threshold as the moment at which the measurement carried out A, which was previously lower than the threshold, exceeds the threshold As.

More particularly, in the example shown in the , the processor is configured to cause the recording of the measurements acquired during a time interval 36 comprising the instant of exceeding the threshold As, a first duration d1 before exceeding the threshold As and a second duration d2 after exceeding the threshold As.

The first duration d1 is, for example, less than 5 seconds, more particularly between 0.5 and 2 seconds.

The second duration d2 is, for example, less than 10 seconds, more particularly between 2 and 5 seconds.

The threshold As, the first duration d1 and the second duration d2 are, for example, adjustable.

This allows data to be recorded only when something is detected by at least one sensor, and not continuously.

This severely limits the amount of data that can be recorded and then transmitted and processed.

Alternatively, the processor is configured to record all acquired measurements.

Alternatively, the processor is adapted to operate in a first mode in which it records data only when a threshold is exceeded, as described above, and in a second mode in which it records all of the measurements acquired.

Here, the processor 26 is further configured to receive instructions from the surface unit via the communication module 24, the processor 26 being configured to execute the instructions.

More particularly, the communication module 24 is adapted to receive and transmit an acoustic wave to the processor 26, as described previously.

The acoustic wave comprises, for example, an instruction to communicate acquired measurements stored in the memory and/or an instruction to adjust at least one parameter of the monitoring unit according to an instruction.

The at least one parameter includes, for example, the threshold As, the first duration d1, the second duration d2, the acquisition frequency, the acquisition resolution and/or the gain.

The at least one parameter further includes, for example, the recording mode: continuously or only around a threshold exceedance.

The processor is then able to communicate the desired measurements and/or to adjust at least one parameter of the monitoring unit according to the instruction.

In one embodiment, the monitoring unit 10 is provided with an identifier.

The instruction provided by the surface unit includes, for example, the identifier(s) concerned by the instruction. The processor is then able to compare the identifier(s) concerned with the identifier of the monitoring unit, and to execute the instruction if the identifier is included in the list of the identifier(s).

The processor executes, for example, software or a software brick, i.e. in the form of one or more computer programs. Then, it is, for example, also capable of being recorded on a medium, not shown, readable by a computer. The computer-readable medium is, for example, a medium capable of storing electronic instructions and of being coupled to a bus of a computer system. By way of example, the readable medium is an optical disk, a magneto-optical disk, a ROM memory, a RAM memory, any type of non-volatile memory (for example EPROM, EEPROM, FLASH, NVRAM), a magnetic card or an optical card. A computer program comprising software instructions is then stored on the readable medium.

Alternatively, the processor comprises, for example, modules each produced in the form of a programmable logic component, such as an FPGA (Field Programmable Gate Array), or in the form of a dedicated integrated circuit, such as an ASIC (Application Specific Integrated Circuit).

The power supply 28 comprises, for example, at least one battery.

The power supply 28 here supplies, directly and permanently, the modem 30, each of the sensors 18, 20 and the processor 26.

This allows in particular that any threshold exceedance is detected and/or any message likely to be received by the modem is received.

Power supply 28 is suitable for powering the monitoring unit for at least one year.

The monitoring unit 10 further comprises at least one, here a, buoy 38 connected to the rest of the monitoring unit 10 by a deployable support system 40.

The remainder of the monitoring unit 10 here forms the main body of the monitoring unit 10.

Buoy 38 includes an acoustic receiver, and here in addition a separate battery.

The acoustic receiver is independent and specific to the buoy.

The deployable support system 40 is adapted to be deployed after reception by the monitoring unit 10, here more particularly by the independent acoustic receiver, of an acoustic deployment signal.

The deployable support system 40 comprises, for example, at least one cable or rope fixed at one free end to the buoy 38 and at another end linked to the remainder of the monitoring unit 10.

The cable or rope is, for example, wound or folded into a compartment 42.

The cable or rope is kept folded or coiled in this way.

Upon receipt of an acoustic deployment signal, the cable or rope is released, so that it deploys by the buoyancy force applied by the buoy at the free end. It is held at its bound end by the remainder of the monitoring unit 10.

The buoy 38 then floats above the remainder of the monitoring unit 10. More particularly here, the cable or rope is here of such a dimension that the buoy floats on the surface, including when the remainder of the monitoring unit 10 is on the seabed. The cable or rope has, for example, a length of between 100 m and 1,000 m.

In the example shown, the monitoring unit 10 further comprises a clip 44.

The clip 44 is adapted to be grasped, so as to manipulate the monitoring unit.

The fastener 44 is, for example, a flexible or rigid cable or a hook.

The fastener 44 is, for example, fixed to the flotation plate 16.

The attachment 44 is here adapted to be fixed to a complementary attachment 46, here a hook, connected to a lifting device 48, for example by a cable.

The complementary fastener 46 is acoustically triggered release, that is to say it is adapted to release the fastener 44 in the event of receipt of an acoustic release signal.

The lifting apparatus 48 is adapted to handle the monitoring unit 10, in particular, to move it close to a given location on the seabed.

The complementary attachment 46 is provided with an underwater positioning system, for example an underwater acoustic positioning system, for example a USBL (for Ultra-Short BaseLine in English) or SSBL (for Super Short BaseLine in English) system.

Alternatively, the monitoring unit is provided with such a system.

The underwater positioning system here comprises a transponder or a receiver on the element to be positioned, here the complementary attachment 46 or the monitoring unit, a surface unit being provided with a corresponding transceiver, the position of the positioning system being measured relative to the transceiver by transmission of acoustic waves.

A method for monitoring an underwater subsoil of a body of water according to one embodiment will now be described, in particular with regard to FIGS. 4 to 7.

The monitoring process includes the following steps:

- deployment of at least one 10 surveillance unit,

- emission of acoustic waves 120 into the body of water by an acoustic source 122, and

- reception of a wave reflected by at least one monitoring unit.

The monitoring method further comprises a step of recording measurements acquired by the at least one sensor of the at least one monitoring unit.

The monitoring method further comprises a step of transmitting the measurements recorded by the at least one monitoring unit to a collection surface unit.

An example of deploying a plurality of monitoring units is shown in .

Each monitoring unit 10 is as described above.

The or each monitoring unit 10 is deposited on a seabed 110 at a respective target location of said seabed.

The subsoil of the seabed presents a geophysical structure 112 to be monitored, for example a reservoir, which more particularly includes places of particular interest 114.

Surveillance units are deployed one by one.

More specifically, each monitoring unit is placed in turn on the seabed at its respective target location.

The respective target locations depend in particular on the geophysical structure 112, and possibly on the locations of particular interest 114.

Each monitoring unit is, for example, pre-configured, for example for acquisition and/or recording parameters, for example the acquisition frequency and resolution.

The acquisition frequency is, for example, equal to 500 Hz.

The monitoring unit is, for example, additionally associated with a unique identifier.

In addition, a respective target location is assigned to the monitoring unit.

The initial parameters, the identifier and/or the target location are, for example, stored in the memory 22.

The battery(ies) of the power supply 28 of the monitoring unit 10 is here pre-charged.

The monitoring unit 10 is connected to a deployment surface unit, more particularly to a lifting device 48, here a winch, so that the lifting device is suitable for handling the monitoring unit 10.

The lifting apparatus 48 is arranged on the surface of the water. More particularly, the lifting apparatus 48 is, for example, arranged on a ship or a floating platform.

The monitoring unit 10 is here connected to the lifting device 48 via a tether 46 with remotely controllable release, more particularly a tether with acoustically triggered release.

More particularly, the attachment 46 holds the monitoring unit 10, more particularly by the attachment 44 of the monitoring unit 10.

The attachment 46 is connected to the lifting apparatus 48 by a cable 116. The lifting apparatus 48 is adapted to control the winding and unwinding of the cable 116.

The monitoring unit 10 is immersed in the span, the monitoring unit 10 being held by the lifting apparatus 48.

The lifting device 48 gradually unwinds the cable 116, so that the monitoring unit descends into the water by gravity.

A representative position of the monitoring unit location is monitored.

For example, the tether 46 or the monitoring unit 10 is provided with an underwater positioning system, for example an underwater acoustic positioning system, for example a USBL (for Ultra-Short BaseLine in English) or SSBL (for Super Short BaseLine in English) system, as described above.

The corresponding transceiver is, for example, arranged on the deployment surface unit, e.g. the ship or platform, so that the relative position of the positioning system to the transceiver is known.

The location of the monitoring unit is here inferred from the relative position.

The monitoring unit is then arranged above the respective target location by the lifting device, for example from a distance of less than 10 meters, for example less than 5 meters.

Above here is understood to mean that the monitoring unit is arranged directly above the target location depending on the severity of the location.

The deployment of the surveillance unit then includes the dropping of surveillance unit 10.

More particularly, an acoustic release signal is emitted, for example by the surface unit, and received by the attachment 46.

The fastener 46 then releases the monitoring unit 10.

The monitoring unit 10 then finishes descending to the target location on the seabed 110 by gravity.

The base plate 14 then rests on the seabed 110.

In one embodiment, the descent is, for example, assisted by a remotely controlled vehicle 118, more particularly a remotely operated underwater vehicle or ROV (for Remotely Operated underwater Vehicle in English).

The vehicle 118 is, for example, provided with an optical device 120, for example a camera, adapted to observe the monitoring unit 10 during the descent.

This allows in particular to verify that the descent of the surveillance unit goes well, as well as the correct deposit of the surveillance unit at the target location.

In a particular embodiment, the vehicle 118 is, for example, adapted to move the monitoring unit 10 held by the lifting apparatus 48 before the drop, so as to refine the location of the monitoring unit before the drop.

After depositing a monitoring unit, the lifting device 48 raises the attachment 46. More specifically, the cable 116 is wound up again, here with the maximum operating speed.

The lifting apparatus 48, here the ship provided with the lifting apparatus 48, is moved above a target location of another monitoring unit, said other monitoring unit then being attached to the lifting apparatus 48, more particularly via the attachment 46.

These steps are repeated to drop all the monitoring units to their respective target locations.

Then, at least one measurement campaign is carried out with the monitoring units, as shown in the .

An acoustic source 122 adapted to generate acoustic waves 120 in the body of water, in particular in the form of shots, is provided.

The acoustic source 122 is, for example, provided with a hydrophone.

The hydrophone is suitable for measuring the acoustic waves emitted by the acoustic source, and in particular each of the shots made.

The hydrophone is connected to or includes a memory and a clock, the measurements made by the hydrophone being recorded in the memory with a corresponding timestamp of the clock. More specifically, each detected shot is recorded with the corresponding timestamp.

This makes it possible in particular to compare the direct measurements of the shots at the level of the acoustic source 122 and the measurements acquired by each monitoring unit 10, during the subsequent exploitation of the measurements.

The link between said clock and clock 34 is known. In particular, each clock presents the exact time in a time scale, here the same scale, for example in a given time zone.

The acoustic source 122 is deployed from the surface, more particularly from a platform, a floating unit 124 or a ship.

In the example shown, the acoustic source is deployed from a floating unit 124 where a well opens towards the geophysical structure 112.

The acoustic source 122 is held by a lifting device 126, here a winch, here by means of a cable 128.

The acoustic source 122 is immersed in the expanse, so that the acoustic waves propagate to the seabed 110.

The acoustic source is, for example, immersed at a depth of between 1 and 20 meters, more particularly between 5 and 10 meters.

The acoustic source is, for example, arranged at a distance from the geophysical structure, more particularly from at least one location of particular interest 114, of less than 1.0 kilometer.

The acoustic source 122 then emits acoustic waves 120, for example at a given frequency and for a given duration.

The given frequency is, for example, such that a blast of acoustic waves is made every 30 seconds to 5 minutes, for example every minute.

The given duration is between 15 minutes and 5 hours, for example between 30 minutes and 2 hours, for example equal to one hour.

The given duration depends in particular on weather and water conditions.

The acoustic waves 120 emitted by the acoustic source 122 propagate to the seabed 110 and are partly reflected, for example by the geophysical structure 112, and in particular at locations of particular interest 114.

The reflected wave is received by at least one of the at least one monitoring unit 10 and measured by the at least one sensor 18, 20 of said monitoring unit 10.

The measurements acquired by the at least one sensor of the at least one monitoring unit are recorded.

More particularly, as described above, the recording in the memory 22 of the measurements acquired by the at least one sensor 18, 20 is carried out when the acquired measurements exceed a threshold As.

Each peak corresponding to a threshold exceedance corresponds, for example, here to a burst of acoustic waves.

This makes it possible, in particular, to record only the relevant acquired measurements, and thus to reduce the size of the recorded data.

In particular, by recording the measurements acquired one second before the threshold is exceeded and three seconds after the threshold is exceeded, and a shot is made every minute for one hour, then the recorded measurements correspond to 240 seconds per hour, or 4 minutes, instead of one hour of recording.

Furthermore, considering that a campaign is carried out once a month, this means that after a year, the equivalent of 48 minutes of acquisition are recorded, compared to a full year in the case where everything is recorded continuously.

Alternatively, all acquired measurements are recorded.

At the end of the measurements, the acoustic source 122 is removed. More specifically, it is brought back to the surface.

The previous steps of providing an acoustic source, emitting acoustic waves into the range and measuring are, for example, repeated, corresponding to a measurement campaign. This makes it possible to monitor the evolution of the measurements over time, and thus of the structure being monitored.

With the monitoring units remaining in place between campaigns, subsequent campaigns are simple to implement, simply by providing an acoustic source, and precise, with the units remaining in their location between campaigns.

A step of transmitting the measurements recorded by the at least one monitoring unit 10 to a collection surface unit 130 is shown in the .

The collection surface unit 130 is, for example, a platform, a floating unit or a vessel.

The collection surface unit 130 is, for example, the same unit from which the acoustic source 122 is deployed.

More particularly, an acoustic modem 132, i.e. adapted to transform an electronic signal into an acoustic wave emitted in the water surrounding the monitoring unit, and here vice versa, is deployed, here from the collection surface unit 130.

The acoustic modem 132 is held by a lifting device 134, here a winch, here by means of a cable 136. The lifting device is, for example, identical to the lifting device 126 used to deploy the acoustic source 122.

The acoustic modem 132 is, for example, immersed to a depth of between 1 and 20 meters, more particularly between 5 and 10 meters.

The acoustic modem 132 is arranged such that the monitoring units whose data transmission is desired are present within the range of the acoustic modem 132.

The acoustic modem 132 is, for example, arranged at a distance from at least one of the monitoring units of less than 1.0 kilometer, more particularly at a distance from the monitoring units whose data transmission is desired of less than 1.0 kilometer .

The acoustic modem 132 emits a collection instruction acoustic wave into the range.

The collection instruction acoustic wave comprises an instruction to communicate acquired measurements stored in the memory, more particularly for a given monitoring unit(s). The identifier of the given monitoring unit(s) is included in the collection instruction acoustic wave.

The collection instruction acoustic wave further comprises, for example, an identifier specific to the acoustic modem 132 or the collection surface unit 130 or a location of the acoustic modem.

In one embodiment, the collection instruction further comprises a time interval of the measurements to be transmitted, here in the time scale of the clock 34.

The time interval is, for example, strictly speaking an interval of time or a past instant, the time interval then being the interval between said past instant and the present.

The collection instruction acoustic wave is received by the monitoring units within the range of the acoustic modem 132, more particularly detected and transformed by the acoustic modem 30 and here transmitted to the processor 26.

Each monitoring unit, more particularly the processor 26, analyzes the transformed collection instruction acoustic wave. It detects, for example, in particular the instruction to communicate acquired measurements stored in the memory.

For example, it also detects the presence or absence of the unique identifier of the monitoring unit.

If the unique identifier of the monitoring unit is absent, the monitoring unit 10 does not transmit the measurements in its memory 22.

If the unique identifier of the monitoring unit is present, the monitoring unit 10 transmits the measurements stored in its memory 22 via the acoustic modem 30, more particularly all of the measurements stored in its memory 22 or the measurements stored in the time interval included in the collection instruction where applicable.

More particularly, the processor 26 controls the transformation into acoustic waves and the emission of the measurements to be transmitted by the acoustic modem 30.

The measurements are, for example, sent in successive packets. Each packet has a given maximum size.

Each packet is, for example, identified by a number i, corresponding for example to its rank within the set of packets.

Packet measurements and packets are, for example, in chronological order of the timestamp of each measurement or in reverse chronological order.

The acoustic modem 132 then receives the acoustic waves corresponding to the stored measurements transformed and emitted by the monitoring unit 10.

The acoustic modem 132 transforms these acoustic waves back into the measurements stored by the monitoring unit.

These measurements are then, for example, recorded in a memory connected to the acoustic modem 132, for example directly or by transmission to a module within the collection surface unit 130, the module comprising a memory in which this data is stored.

Advantageously, the acoustic wave transmission protocol includes a cyclic redundancy check, or CRC.

In an alternative embodiment, the collection instruction acoustic wave does not include an identifier of a particular monitoring unit or units. Then, all monitoring units present within the range of the acoustic modem 132 and not having already transmitted their stored measurements transmit their stored measurements.

When only an interval around a threshold exceedance is recorded, this allows the volume of data to be transmitted to be greatly reduced.

For example, considering an acquisition frequency of 500 Hz and a resolution of 16 bits, or 2 bytes, the data recorded during a campaign and corresponding to 4 minutes of recording represent 240 KB and the data recorded for a year and corresponding to 48 minutes of recording represent 3 MB, compared to more than 30 GB for continuous recording for a year.

An underwater acoustic modem, for example, has a data transmission speed of 400 bits per second. The transmission of data corresponding to a campaign is then carried out in 1 hour 20 minutes, while the transmission of data from a continuous recording for one hour would take 20 hours.

Thus, recording only the measurements acquired around a threshold exceedance is particularly advantageous for remote transmission of data from the monitoring unit.

Furthermore, data transmission is energy-intensive, so reducing transmission time saves battery power.

Additionally, this helps reduce the amount of data that needs to be processed subsequently.

In a particular embodiment, the method comprises a step of changing the parameters of the monitoring unit 10.

An acoustic modem similar to the 132 acoustic modem of data transmission emits an adjusting acoustic wave.

The adjustment acoustic wave comprises an instruction to adjust at least one parameter of at least one monitoring unit according to a setpoint, more particularly for one or more given monitoring units.

The at least one parameter comprises, for example, the threshold As, the first duration d1, the second duration d2, the acquisition frequency, the acquisition resolution and/or the gain. The at least one parameter further comprises, for example, the recording mode: continuously or only around a threshold exceedance.

The identifier of the given monitoring unit(s) is included in the setting instruction.

The adjustment acoustic wave is received by the monitoring units within the range of the transmitting acoustic modem, more particularly detected and transformed by the acoustic modem 30 and here transmitted to the processor 26.

Each monitoring unit, more particularly the processor 26, analyses the transformed adjustment acoustic wave. It detects, for example, in particular the adjustment instruction.

For example, it also detects the presence or absence of the unique identifier of the monitoring unit.

If the unique identifier of the monitoring unit is present, the parameters of said monitoring unit 10 are modified according to the instructions.

If not, the at least one parameter is not modified.

In an alternative embodiment, the adjustment acoustic wave does not include an identifier of a particular monitoring unit or units. Then, all of the monitoring units 10 present within the range of the transmitting acoustic modem modify their parameters according to the instruction.

This allows in particular to modify parameters without having to retrieve the monitoring unit. This is particularly advantageous when after an initial campaign, it appears that parameters different from the parameters previously set in the monitoring unit would be more appropriate for the desired monitoring. For example, it is noted that the acquisition frequency is insufficient compared to the data processing carried out subsequently. The parameters of the monitoring unit 10 can then easily be modified remotely.

In one embodiment, the method further comprises successive steps of recovering the at least one monitoring unit, according to an example shown in the .

Such recovery is, for example, performed when the battery power supply of the monitoring unit is below a threshold value and/or if it is planned to redeploy the monitoring unit to a different location.

When the battery of the power supply 28 of the monitoring unit 10 is below a threshold value, the monitoring unit 10 sends, for example, an alert via the acoustic modem 30, here to the surface. This allows an acoustic modem deployed from the surface to be informed of the low battery level in order to plan the future ascent of the monitoring unit.

In the event that there is no acoustic modem deployed from the surface, the monitoring unit then goes into standby mode. It then periodically sends alerts via the acoustic modem. Alternatively, it no longer sends alerts and remains in standby mode without sending alerts until it is recovered.

An acoustic deployment signal is emitted, here by a surface unit or an acoustic modem deployed by a surface unit.

The acoustic deployment signal is, for example, emitted for a given monitoring unit(s). The identifier of the given monitoring unit(s) is included in the acoustic deployment signal.

The acoustic deployment signal is received by the monitoring units within the acoustic signal transmission range, more particularly by their acoustic receivers independent of the buoys 38.

Each unit receiving the acoustic deployment signal detects the presence or absence of its identifier in the acoustic deployment signal.

If the identifier is missing, nothing happens.

If the identifier is present, following receipt by the monitoring unit 10 of the acoustic deployment signal, the deployable maintenance system 40 of the buoy 38 is deployed.

Buoy 38 is pulled towards the surface by its buoyancy.

The deployable support system 40 has a length such that the buoy 38 is driven until it floats on the surface.

The monitoring unit is then recovered by pulling the buoy 38 or the deployable support system 40.

More particularly, a lifting device, here a winch, grabs the buoy 38 or the deployable support system 40, which are easily accessible, and pulls so as to raise the monitoring unit to the surface.

Alternatively, following receipt by one or more monitoring units 10 of the acoustic deployment signal, the deployable holding system 40 of the buoy 38 is deployed for each of these monitoring units. The acoustic deployment signal then does not include an identifier of one or more monitoring units.

Alternatively, the acoustic deployment signal is emitted directly by the acoustic modem 30 of the monitoring unit 10, when the power supply battery reaches a critical level.

Alternatively, the processor 26 directly sends deployment instructions to the deployable support system 40, for example by a wired connection. The processor 26 sends, for example, these instructions when the battery of the power supply reaches a critical level.

This then makes it easy to retrieve the monitoring unit, for example to recharge or change the battery.

On this occasion, it is also possible to download all the data recorded in the memory of the monitoring unit.

Any other maintenance intervention may also be carried out.

The surveillance unit is then likely to be deployed again, either to the same location or to another location.

A monitoring unit according to the invention thus makes it possible to carry out several campaigns, for example to monitor the evolution of the geophysical structure, without requiring the recovery of the monitoring units at the end of each campaign and their redeployment at the start of the following campaign. This is thus much simpler to implement, less costly in terms of time and resources. In addition, between campaigns, the monitoring units remain on site, so that there is no uncertainty about the location of their redeployment.

Claims (11)

A monitoring unit (10) of an underwater subsoil, the monitoring unit (10) being adapted to be placed on a seabed (110), the monitoring unit (10) comprising at least one sensor (18, 20), preferably at least one geophone (18) or at least one hydrophone (20), characterized in that the monitoring unit (10) comprises a memory (22) and a communication module (24) adapted to communicate wirelessly with a surface unit. A monitoring unit according to claim 1, wherein the communication module (24) is adapted to communicate via water with the surface unit. Monitoring unit according to claim 1 or 2, wherein the communication module (24) comprises an acoustic modem (30). Monitoring unit according to any one of claims 1 to 3, comprising a processor (26) configured to manage the acquisition of measurements by the at least one sensor (18, 20), the recording of the acquired measurements in the memory (22) and the communication by the communication module (24). Monitoring unit according to claim 4, wherein the processor (26) is configured to trigger the recording of the acquired measurements when the acquired measurements exceed a threshold (As). Monitoring unit according to claim 5, wherein the processor (26) is configured to cause the recording of the measurements acquired during a time interval comprising the instant of exceeding the threshold (As), a first duration (d1) before exceeding the threshold (As) and a second duration (d2) after exceeding the threshold (As). A monitoring unit according to any one of claims 4 to 6, wherein the processor (26) is configured to receive from the communication module (24) instructions received by the communication module (24), the processor (26) being configured to execute the instructions. A monitoring unit according to any one of claims 1 to 7, comprising at least one buoy (38), the buoy (38) being connected to a main body of the monitoring unit (10) by a deployable holding system (40), the deployable holding system (40) being adapted to be deployed after the monitoring unit (10) receives an acoustic deployment signal. A method of monitoring an underwater subsoil of a body of water, comprising the following steps:
- deployment of at least one monitoring unit (10) according to any one of claims 1 to 8, the at least one monitoring unit (10) being deposited on a seabed (110) at a respective target location,
- emission of acoustic waves (120) into the body of water by an acoustic source (122), and
- reception of a wave reflected by the at least one monitoring unit (10). A monitoring method according to claim 9, wherein deploying the at least one monitoring unit (10) comprises placing the corresponding monitoring unit (10) above the respective target location by a lifting apparatus (48), and dropping the monitoring unit (10). Monitoring method according to claim 9 or 10, comprising a step of recovering the at least one monitoring unit (10), the at least one monitoring unit (10) comprising at least one buoy (38), the buoy (38) being connected to a main body of the monitoring unit (10) by a deployable holding system (40), the deployable holding system (40) being adapted to be deployed after the monitoring unit receives an acoustic deployment signal, the recovery step comprising the emission of an acoustic deployment signal, the deployment of the deployable holding system (40) and the recovery of the monitoring unit (10) by pulling the buoy (38) or the deployable means system (40).