Autonomous mobile platform-based seabed magnetotelluric detection method and device

Abstract

The application discloses a seabed magnetotelluric detection method and device based on an autonomous mobile platform. The autonomous mobile platform is provided with a magnetotelluric detection load, and comprises the following steps: at a preset station, a laying mechanism installed on the autonomous mobile platform is controlled to act, and an electric field sensor group and a magnetic field sensor group are laid; original time sequence data sent by a data acquisition module is received; the original time sequence data is preprocessed to obtain impedance results, and the data quantity of the impedance is far less than that of the original time sequence data; the impedance is transmitted to a communication submersible, and the communication submersible is controlled to float to the water surface, and the impedance is sent to a water surface receiving end. The scheme has high operation efficiency, high precision, strong environmental adaptability and high data real-time performance.

Description

Technical Field

[0001] This invention relates to the field of marine geophysical exploration technology, and in particular to a method and apparatus for seabed magnetotelluric exploration based on an autonomous mobile platform. Background Technology

[0002] Seafloor magnetotelluric (MTT) detection is an important and effective means of exploring the deep structure of the ocean floor, offering advantages such as large detection depth, high sensitivity in identifying high-conductivity anomalies, high operational efficiency, and low operating costs. Current operations primarily utilize seafloor electromagnetic receivers to conduct in-situ magnetotelluric signal observations. These receivers are equipped with electromagnetic sensors, a data acquisition chamber, and a hydroacoustic release device for self-contained data acquisition. The current method involves deploying multiple receivers (typically around 30 units) on a work vessel at a time, deploying them one by one after reaching the designated location, allowing them to operate on the seabed for a period (usually two weeks), and then retrieving them sequentially for data preprocessing.

[0003] The current operating mode has the following limitations:

[0004] ① Low signal-to-noise ratio in electric field measurements. Due to limitations in deck working space and receiver cabin mechanical structure, the receiver electrode spacing is short (generally 8 to 10 m), which limits the signal-to-noise ratio of electric field signal observation and leads to a decrease in detection capability.

[0005] ② Magnetic field measurements are susceptible to electromagnetic interference. The high-sensitivity magnetic sensor is located close to the data acquisition chamber, posing an electromagnetic compatibility risk and causing a decrease in the magnetic track signal-to-noise ratio.

[0006] ③Low operational efficiency and high cost. Carrying about 30 receivers at a time, deploying and retrieving them one by one, occupies a large deck area, consumes a lot of ship time, is highly dependent on the mother ship, is easily affected by weather and sea conditions, and poses a risk to the safe retrieval of the instruments.

[0007] ④ Limited survey area. Traditional surface vessels have difficulty getting close enough to deploy equipment in disputed waters.

[0008] Therefore, it is urgent to overcome the obstacles of existing technical solutions and seek a high-precision, high-efficiency, autonomous and intelligent detection method and device. Summary of the Invention

[0009] The purpose of this invention is to provide a method and device for seabed magnetotelluric detection based on an autonomous mobile platform.

[0010] To achieve the above objectives, in a first aspect, the present invention provides a method for seabed magnetotelluric detection based on an autonomous mobile platform, wherein the autonomous mobile platform is equipped with a magnetotelluric detection payload, and includes the following steps:

[0011] S1: At the preset station, control the deployment mechanism installed on the autonomous mobile platform to deploy the electric field sensor group and magnetic field sensor group in the magnetotelluric detection payload outside the autonomous mobile platform body respectively.

[0012] S2: After the electric field sensor group and magnetic field sensor group are deployed, the raw time series data sent by the data acquisition module is received. The raw time series data is obtained by the data acquisition module from sampling and quantizing the seabed magnetotelluric signal. The seabed magnetotelluric signal is acquired by the deployed electric field sensor group and magnetic field sensor group.

[0013] S3: Preprocess the original time series data to obtain impedance results. The amount of impedance data is much smaller than the amount of original time series data.

[0014] S4: Transmit the impedance to the communication buoy mounted on the autonomous mobile platform, and control the communication buoy to rise to the surface of the water, and send the impedance to the surface receiver.

[0015] In one embodiment of the present invention, before step S1, the method further includes:

[0016] S01: Obtain the preset task list, which includes the coordinates of multiple preset stations;

[0017] S02: Based on the coordinates of the current preset station to be measured, control the autonomous mobile platform to navigate to the preset station.

[0018] In one embodiment of the present invention, after step S4, the method further includes:

[0019] S5: Control the deployment mechanism to retrieve the electric field sensor group and the magnetic field sensor group, and control the autonomous mobile platform to navigate to the next preset station according to the preset task list. Repeat steps S1 to S4 until all preset station tasks in the preset task list are completed.

[0020] In one embodiment of the present invention, the electrode spacing formed after the electric field sensor group is deployed is greater than 10m.

[0021] The magnetic field sensor array was laid out in the seabed sediments according to the expected direction.

[0022] In one embodiment of the present invention, the electric field sensor group includes a plurality of electric field sensors, which are arranged in mutually perpendicular directions to form two sets of orthogonal electric field measurement lines.

[0023] The mutually perpendicular directions are controlled within a preset angle range by a laser positioning device.

[0024] In one embodiment of the present invention, two sets of redundant electric field sensors are arranged in each direction.

[0025] In one embodiment of the present invention, before the data acquisition module is started, the method further includes: controlling the power module, navigation module and underwater acoustic communication module of the autonomous mobile platform to shut down or enter a low-power standby state.

[0026] The electric field sensor group and magnetic field sensor group were calibrated in situ after being deployed and placed.

[0027] In a second aspect, the present invention provides an apparatus for use in the seabed magnetotelluric detection method based on an autonomous mobile platform as described in the first aspect, the apparatus comprising:

[0028] The magnetotelluric detection payload includes: an electric field sensor group, a magnetic field sensor group, a data acquisition module, and a data preprocessing module.

[0029] Electric field sensor array and magnetic field sensor array are used to collect magnetotelluric signals from the seabed;

[0030] The data acquisition module is electrically connected to the electric field sensor group and the magnetic field sensor group. It is configured to perform equal-interval sampling and quantization of the seabed magnetotelluric signal after the electric field sensor group and the magnetic field sensor group are deployed and in place, so as to obtain the raw time series data.

[0031] The data preprocessing module is connected to the data acquisition module and is configured to preprocess the raw time series data to obtain impedance results. The amount of impedance data is much smaller than the amount of raw time series data.

[0032] The autonomous mobile platform is equipped with a magnetotelluric detection payload. The autonomous mobile platform includes: the platform body, the deployment mechanism, the communication mooring, and the control system. The deployment mechanism, the communication mooring, and the control system are all located on the platform body.

[0033] The deployment mechanism is mechanically connected to the electric field sensor group and the magnetic field sensor group, and is configured to deploy the electric field sensor group and the magnetic field sensor group outside the autonomous mobile platform body after arriving at the preset station.

[0034] The communication buoy is connected to the data preprocessing module, configured as a receiving impedance, and can be released to float to the surface to send the impedance to the surface receiver.

[0035] The control system is connected to the autonomous mobile platform, the deployment mechanism, the data acquisition module, the data preprocessing module, and the communication buoy control, and is configured to execute the method steps as described in the first aspect.

[0036] In one embodiment of the present invention, the deployment mechanism includes a laser positioning device, which is installed on the platform body and is used to measure the deployment direction during the deployment of the electric field sensor group and the magnetic field sensor group to ensure that the included angle of each direction is within a preset angle range.

[0037] In one embodiment of the present invention, the autonomous mobile platform further includes an underwater acoustic communication module, a navigation and positioning module, an energy and power module, and a motor mechanism;

[0038] The underwater acoustic communication module is used to communicate with the shipborne USBL positioning array on the surface to achieve underwater positioning and tracking of the autonomous mobile platform.

[0039] The navigation and positioning module includes an inertial navigation unit and / or a Doppler velocimeter, used to provide real-time position and heading information in underwater environments without satellite signals;

[0040] The power module includes a battery pack to power the autonomous mobile platform and the magnetotelluric detection payload;

[0041] The motor mechanism includes a propeller or tracked walking mechanism, used to drive the autonomous mobile platform to navigate in water or walk on the seabed.

[0042] Compared with existing technologies, the seabed magnetotelluric detection method based on an autonomous mobile platform according to the present invention achieves autonomous detection of seabed magnetotelluric signals and near real-time data transmission through a complete process of sensor deployment, data acquisition, preprocessing and transmission, thus eliminating the traditional method's full dependence on the mother ship. Attached Figure Description

[0043] Figure 1 This is a flowchart illustrating a seabed magnetotelluric detection method based on an autonomous mobile platform according to an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram of the structure of a seabed magnetotelluric detection device based on an autonomous mobile platform according to an embodiment of the present invention.

[0045] Figure 3 This is a schematic diagram of the tracked recovery structure in this invention;

[0046] Figure 4 This is a schematic diagram of the underwater operation of the present invention (sensor deployment stage);

[0047] Figure 5 This is a schematic diagram of the underwater operation of the present invention (the buoy communication release phase).

[0048] Figure 6 This is a schematic diagram of the underwater operation of the present invention (device deployment stage). Detailed Implementation

[0049] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0050] Unless otherwise expressly stated, throughout the specification and claims, the term "comprising" or its variations such as "including" or "comprises" shall be understood to include the stated elements or components without excluding other elements or other components.

[0051] Current seabed magnetotelluric surveys are generally conducted using seabed electromagnetic receivers, which are limited by factors such as electric field measurement electrode spacing, battery capacity, sea conditions, and weather, resulting in low signal-to-noise ratio and low operational efficiency.

[0052] This application combines a magnetotelluric (MT) detection payload with an autonomous mobile platform, and configures a deployment mechanism, an online data preprocessing module, and a communication mooring buoy to achieve autonomous surveying and long-term MT detection under seabed conditions. It has the capability to autonomously complete data acquisition from multiple measurement points with a single deployment, and to transmit the data preprocessing results back in near real-time impedance, significantly improving the measurement accuracy and operational efficiency of seabed MT operations, thus revolutionizing traditional MT operation methods. The device mainly consists of an autonomous mobile platform and a MT detection payload. The autonomous mobile platform includes a surface-based shipborne control terminal, a shipborne UBSL positioning array, and the underwater platform body. The underwater portion of the autonomous mobile platform also includes a navigation and positioning module, a power module, an underwater acoustic communication module, a deployment mechanism, and a communication mooring buoy. The MT detection payload includes an electric field sensor group, a magnetic field sensor group, a data acquisition module, a data preprocessing module, and cables. The offshore operation process is as follows: ① Before launching the device, the MT detection payload is installed on the autonomous mobile platform, and a self-check and pre-set operation task list are imported. ② After setup, the platform uses its own power to travel to the preset station, deploys the large-pole-gap electric field sensor, and buries the magnetic field sensor, beginning the magnetotelluric signal measurement at the first station. ③ After continuous observation at the first station for a certain period (generally two weeks), the electric field and magnetic field sensors are retrieved. The magnetotelluric detection payload completes data preprocessing and transmits the impedance file to the autonomous mobile platform. The platform releases the communication buoy to the water surface and transmits the impedance file to the shore station. ④ The platform autonomously navigates to the next station and repeats step ③ until all preset stations are completed. ⑤ After all tasks in the preset task list are completed, the autonomous mobile platform waits in place for instructions from the work vessel for retrieval and salvage.

[0053] like Figure 1 The diagram shown is a flowchart illustrating a preferred embodiment of a seabed magnetotelluric detection method based on an autonomous mobile platform according to the present invention. Figure 2 The device shown is applied to the above-mentioned seabed magnetotelluric detection method based on an autonomous mobile platform.

[0054] Reference Figure 2 The seabed magnetotelluric detection device based on an autonomous mobile platform includes:

[0055] The magnetotelluric detection payload includes: an electric field sensor group, a magnetic field sensor group, a data acquisition module, and a data preprocessing module.

[0056] Electric field sensor array and magnetic field sensor array are used to collect magnetotelluric signals from the seabed.

[0057] Specifically, the electric field sensor group includes several electric field sensors. For example, the electric field sensors can employ Ag / AgCl non-polarizing electrodes to measure the seabed electric field components (Ex, Ey). The magnetic field sensor group includes several magnetic field sensors, including triaxial inductive magnetic sensors and triaxial fluxgate sensors, to measure the seabed magnetic field components (Hx, Hy, Hz).

[0058] The data acquisition module is electrically connected to the electric field sensor group and the magnetic field sensor group. It is configured to perform equal-interval sampling and quantization of the seabed magnetotelluric signals after the electric field sensor group and the magnetic field sensor group are deployed and in place, so as to obtain the raw time series data.

[0059] Specifically, the data acquisition module includes signal conditioning circuits (filtering and amplification), an analog-to-digital converter (ADC), an automatic gain control unit, and a range compensation unit to filter, sample at equal intervals, and quantize the seabed magnetotelluric signals to obtain raw time series data.

[0060] The data preprocessing module communicates with the data acquisition module and is configured to preprocess the raw time series data to obtain impedance results. The amount of impedance data is much smaller than the amount of raw time series data. Here, impedance results refer to the preprocessed data; "much smaller" means that the amount of preprocessed data is less than 0.01% of the original data.

[0061] Specifically, the data preprocessing module preprocesses the raw time-series data. This involves: reading the calibration file and correcting the voltage values ​​in the raw time-series data to their true physical values ​​based on the sensitivity coefficients and phase responses in the calibration file; performing detrending, mean removal, and digital filtering on the corrected time-series data to eliminate DC drift and low-frequency trend terms, and filtering out out-of-band noise; and then obtaining the Carnia apparent resistivity through time-frequency conversion and impedance estimation. This preprocessing reduces the several gigabytes of raw time-series data to a smaller file size, approximately kilobytes. The calibration file, generated by channel calibration of the electric and magnetic field sensor groups before leaving the factory or before operation, records the sensitivity coefficients and phase responses of each sensor at different frequencies. The calibration file is pre-stored in the data preprocessing module or carried on the autonomous mobile platform along with the magnetotelluric detection payload.

[0062] Understandably, both the data acquisition module and the data preprocessing module are integrated into the data acquisition chamber. The data acquisition chamber is a sealed protective shell structure to seal the precision circuit boards of the data acquisition module and the data preprocessing module inside the shell, isolating them from seawater and high pressure, and ensuring the normal operation of the electronic components.

[0063] It's understandable that the data acquisition module can be connected to the electric field sensor group and the magnetic field sensor group via a watertight cable. This watertight cable is a specially designed deep-sea cable with multiple layers of waterproof insulation, steel wire armor (tensile strength), and a corrosion-resistant outer sheath. It ensures that seawater will not seep into the data acquisition module under the high pressure of the seabed, while also withstanding the enormous tensile forces during platform towing and deployment.

[0064] The autonomous mobile platform is equipped with a magnetotelluric detection payload. The autonomous mobile platform includes: the platform body, the deployment mechanism, the communication mooring, and the control system. The deployment mechanism, the communication mooring, and the control system are all located on the platform body.

[0065] The deployment mechanism is mechanically connected to the electric field sensor group and the magnetic field sensor group, and is configured to deploy the electric field sensor group and the magnetic field sensor group outside the autonomous mobile platform body after arriving at the preset station.

[0066] The communication buoy is connected to the data preprocessing module, configured as a receiving impedance, and can be released to float to the surface to send the impedance to the surface receiver.

[0067] Specifically, the communication buoy comprises a float, a satellite communication terminal, a release mechanism, and a watertight data interface. The float provides buoyancy, allowing the buoy to rise autonomously to the surface after release and remain afloat. The satellite communication terminal is the wireless communication hardware for data transmission; after the buoy surfaces, it transmits impedance data to the shore station via a satellite link. The release mechanism secures the buoy to the platform while mounted and releases it upon receiving a command, allowing the buoy to surface. The watertight data interface handles underwater data exchange, providing a physical layer data link between the data preprocessing module and the buoy when mounted on the platform, transmitting impedance files from the data preprocessing module to the buoy. The watertight data interface employs a wet-plug structure, possesses deep-sea pressure-resistant sealing capabilities, and can transmit impedance files between the data preprocessing module and the buoy at a rate of no less than 115200 bps. Upon reaching the surface, the buoy and the shore station transmit data via satellite communication.

[0068] The control system is connected to the autonomous mobile platform, the deployment mechanism, the data acquisition module, the data preprocessing module, and the communication mooring control, and is configured to execute the steps of the seabed magnetotelluric detection method based on the autonomous mobile platform.

[0069] In this embodiment, by deeply integrating the magnetotelluric detection payload with the autonomous mobile platform, a complete autonomous seabed magnetotelluric detection equipment is formed, realizing full automation from sensor deployment to data transmission.

[0070] In one embodiment, the deployment mechanism includes a laser positioning device and an AUV. The laser positioning device is mounted on the platform body and is used to measure the deployment direction during the deployment of the electric field sensor group and the magnetic field sensor group to ensure that the included angle of each direction is within a preset angle range.

[0071] Specifically, the laser positioning device is installed on the outside of the platform body. It emits a laser beam during the deployment of the electric and magnetic field sensors, and determines the deployment direction by measuring the pointing angle of the laser beam. The measurement accuracy of the laser positioning device can reach within ±0.5°, ensuring that the included angle between the four deployment directions is 90°±2°.

[0072] The AUV (Autonomous Vehicle) is used to transport the electric field sensor array from the platform to a predetermined distance and precisely deploy it on the seabed, as well as to push the magnetic field sensor array from the platform and bury it at a location outside the platform. These processes are accomplished by a small AUV. For example, a single AUV can deploy four electric field sensors sequentially, and then return to the platform after deployment. The electric field sensors can be retrieved using a tracked mechanism.

[0073] like Figure 3 As shown, each tracked recovery structure is driven by a rotating shaft through the output of a motor. A track reel is fitted outside the rotating shaft, and a cable is embedded inside the track. Rotating the track reel allows the cable to extend or retract. An electric field sensor is installed at the head of the cable, which is also the head of the track. It should be noted that the track has only one degree of freedom: extension and retraction.

[0074] The specific working principle is as follows: When deploying the electric field sensors, under the guidance of the laser, the AUV drives the electric field sensors and tracks to move to the designated position. After the AUV has deployed the four electric field sensors in sequence, it returns to the platform body. During recovery, the motor drives the rotating shaft to rotate and rewind the tracks back to the track reel.

[0075] The predetermined distance can be set according to actual needs, such as 100 meters, much greater than 10 meters. Specifically, four electric field sensors are placed at a distance of more than 100 meters from the platform body, with every two electric field sensors on the same straight line, and the two straight lines formed are perpendicular to each other, that is, the included angle between the four deployment directions is 90°.

[0076] The magnetic field sensor is located within the platform body. Using the robotic arm of an AUV, the sensor is removed from the body and embedded in a location outside the platform according to the intended orientation. The AUV uses lasers to determine and adjust the sensor's orientation, and an electronic compass to determine and level the sensor's tilt angle. This ensures the sensor's X-axis is parallel to magnetic north, and it is embedded within the seabed sediment, achieving strong coupling between the sensor and the sediment. The sensor is flexibly connected to the platform body via ropes and cables to prevent interference caused by platform vibrations. The intended orientation can be set according to actual needs.

[0077] The magnetic field sensor array is buried in the sediment, which can effectively reduce the mechanical interference caused by the flowing seawater and help improve the signal-to-noise ratio. On the other hand, it can keep the magnetic field sensor array away from the platform body, which helps to suppress the electromagnetic interference of the platform body to the magnetic field sensor.

[0078] The system uses laser to measure the direction, rotates the X component of the magnetic field sensor to the magnetic north direction, so that the X component is maximized and the Y component is minimized, and uses a pre-installed electronic compass to level the magnetic field sensor.

[0079] During recovery, the magnetic sensor is first removed from the seabed sediment and retrieved to the mobile platform body using an AUV, and then the electric field sensor is removed and the electric field sensor cable is retrieved to the platform body using a tracked winch.

[0080] The distance between the buried magnetic field sensor and the platform body can be set according to actual needs, such as 10 meters.

[0081] In this embodiment, a laser positioning device is used to achieve high-precision underwater direction measurement and positioning, overcoming the problem of difficulty in accurately controlling the underwater deployment direction in traditional schemes, ensuring the accuracy of the included angle of orthogonal survey lines, and meeting the theoretical requirements of the magnetotelluric sounding method for the direction of survey lines.

[0082] In one embodiment, the autonomous mobile platform further includes an underwater acoustic communication module, a navigation and positioning module, an energy and power module, and a motor mechanism;

[0083] The underwater acoustic communication module is used to communicate with the shipborne USBL positioning array on the surface to achieve underwater positioning and tracking of the autonomous mobile platform.

[0084] The navigation and positioning module includes an inertial navigation unit and / or a Doppler velocimeter, used to provide real-time position and heading information in underwater environments without satellite signals;

[0085] The power module includes a battery pack to power the autonomous mobile platform and the magnetotelluric detection payload;

[0086] The motor mechanism includes a propeller or tracked walking mechanism, used to drive the autonomous mobile platform to navigate in water or walk on the seabed.

[0087] Specifically, the autonomous mobile platform also includes a surface component, comprising a shipborne control terminal and a shipborne UBSL (Ultra-Short Baseline) positioning array. The platform body, deployment mechanism, communication mooring, control system, underwater acoustic communication module, navigation and positioning module, power module, and maneuvering mechanism are all underwater components.

[0088] The underwater acoustic communication module is used to communicate with the surface-mounted USBL positioning array to achieve underwater positioning and tracking of the autonomous mobile platform. By transmitting and receiving underwater acoustic signals, the module works in conjunction with the mother ship's USBL positioning array, enabling the mother ship to obtain the underwater platform's location information in real time. Simultaneously, the mother ship can send commands to the platform via the underwater acoustic communication module, and the platform's underwater components can also transmit their status (such as location, battery level, and health status) back to the mother ship.

[0089] The navigation and positioning module includes an inertial navigation unit (INS) and / or a Doppler velocimeter (DVL) to provide real-time position and heading information in underwater environments without satellite signals. The INS measures the platform's acceleration and angular velocity, and through integration, obtains the platform's position, velocity, and attitude information. The Doppler velocimeter measures the platform's velocity relative to the seabed by transmitting sound waves and measuring the Doppler frequency shift. The combined use of INS and DVL enables high-precision autonomous underwater navigation.

[0090] The power module includes a battery pack to power the autonomous mobile platform and the magnetotelluric detection payload. The battery pack preferably uses high-energy-density lithium batteries, with the capacity configured according to the operational requirements (e.g., 20kWh or more) to support the energy consumption needs of all operational stages, including platform navigation, sensor deployment and retrieval, data acquisition (12 months), and communication mooring.

[0091] The mobility mechanism includes either a propeller-driven propulsion system or a tracked walking mechanism, used to propel the autonomous mobile platform to navigate in water or on the seabed. Propeller propulsion is suitable for floating movement and is highly efficient when migrating between stations; tracked walking mechanisms are suitable for bottom-based detection and can maintain platform stability when deploying sensors. The two mobility methods can be selected and configured according to actual operational requirements.

[0092] The shipborne control terminal serves as the human-machine interface and surface command center for the entire operating system, typically installed in the experimental cabin or bridge of the mother ship. Before the underwater portion of the autonomous mobile platform is launched, operators can use it to edit and import pre-set task sheets, writing parameters such as the coordinates of each station and data acquisition time into the platform's control system. It can also receive status data transmitted from the platform via an underwater acoustic communication link, displaying the platform's heading, attitude, depth, battery level, and the operational status of each module in real time, either digitally or graphically. Furthermore, in the event of anomalies on the underwater platform (such as deviation from the course or low battery), operators can use it to send emergency commands (such as underwater acoustic commands) to force the platform to surface immediately or modify the task, ensuring equipment safety.

[0093] Shipborne USBL positioning arrays are high-precision underwater acoustic positioning devices commonly used in marine engineering. They are installed on the hull of the mother ship. They provide absolute position references for autonomous mobile platforms, enabling them to perform absolute position calibration and correct inertial navigation drift when the platform reaches a preset location.

[0094] The shipborne control terminal and the shipborne USBL positioning array work together in the following manner:

[0095] After the autonomous mobile platform is launched, the mother ship's operators monitor the platform's status in real time via the shipboard control terminal. When the platform needs to move between stations, the shipboard USBL positioning array transmits an acoustic interrogation signal at a frequency of 1Hz, and the underwater acoustic communication module on the autonomous mobile platform responds to the interrogation signal. Based on the two-way propagation delay of the acoustic signal and the phase difference received by each transducer, the shipboard USBL positioning array calculates the platform's bearing, distance, and depth relative to the mother ship in real time, and displays this information through the shipboard control terminal.

[0096] When the autonomous mobile platform approaches the preset station (e.g., the distance is less than 50m), the USBL positioning data displayed by the shipboard control terminal serves as the absolute reference. This data is then fused with the platform's own inertial navigation / Doppler velocimeter (INS / DVL) data to correct the accumulated error of the underwater autonomous navigation and ensure that the platform's final positioning accuracy is within ±2 meters.

[0097] During sensor deployment and data acquisition, the mother ship can be in a drifting or low-speed dynamic positioning state. The shipboard USBL positioning array works continuously to track the platform's position and prevent the platform from deviating from the preset operating area due to the push of the seabed current.

[0098] The beneficial effects of this embodiment are as follows: the underwater acoustic communication module enables underwater communication and positioning between the platform and the mother ship; the navigation and positioning module (INS / DVL) enables autonomous underwater navigation without relying on satellite signals; the power module provides energy security for the entire operation process; and the motor mechanism (propeller / track) provides a flexible mode of movement to adapt to different seabed terrains and operational needs.

[0099] The following describes the detection method using the aforementioned submarine magnetotelluric detection device based on an autonomous mobile platform.

[0100] Reference Figure 1 A method for seabed magnetotelluric sounding based on an autonomous mobile platform, wherein the autonomous mobile platform is equipped with a magnetotelluric sounding payload, includes the following steps:

[0101] S1: At the preset station, control the deployment mechanism installed on the autonomous mobile platform to deploy the electric field sensor group and magnetic field sensor group in the magnetotelluric detection payload outside the autonomous mobile platform body.

[0102] Specifically, after the autonomous mobile platform reaches the preset location, the control system issues a deployment command. For example... Figure 4 As shown, the deployment mechanism pushes the electric field sensor group outward from the platform body, ensuring that each electric field sensor forms a certain electrode spacing on the seabed. Simultaneously, the deployment mechanism pushes the magnetic field sensor group outward from the platform body, keeping it away from the platform body to avoid electromagnetic interference from the platform itself. The electric field sensor group includes several electric field sensors, and the magnetic field sensor group includes several magnetic field sensors.

[0103] S2: After the electric field sensor group and magnetic field sensor group are deployed, the system receives the raw time series data sent by the data acquisition module. The raw time series data is obtained by the data acquisition module through sampling and quantization of the seabed magnetotelluric signal. The seabed magnetotelluric signal is acquired by the deployed electric field sensor group and magnetic field sensor group.

[0104] Specifically, after the electric field sensor group and magnetic field sensor group are deployed, the sensors begin to sense natural magnetotelluric field signals in the seabed environment. The electric field sensor converts the electric field signal into a voltage signal, and the magnetic field sensor converts the magnetic field signal into a voltage signal. The data acquisition module samples these analog signals at equal intervals and performs amplitude quantization at a preset sampling rate (such as 1Hz, 15Hz, or 150Hz, adjustable in multiple ranges), generating digitized raw time series data. The data acquisition module sends the raw time series data to the data preprocessing module. It can be understood that during data acquisition, data is acquired according to the preset sampling rate and gain, meaning that the acquisition process performs range compensation and automatic gain control based on the signal amplitude.

[0105] S3: Preprocess the original time series data to obtain impedance results. The amount of impedance data is much smaller than that of the original time series data.

[0106] Specifically, the data preprocessing module receives the raw time series data and preprocesses it. Preprocessing includes operations such as detrending, mean removal, digital filtering, time-frequency conversion, impedance estimation, and apparent resistivity calculation. The original time series data is typically several gigabytes to tens of gigabytes in size; after preprocessing, the generated impedance file is reduced to the kilobyte level.

[0107] S4: Transmit the impedance to the communication buoy mounted on the autonomous mobile platform, and control the communication buoy to rise to the surface of the water, and send the impedance to the surface receiver.

[0108] Specifically, after preprocessing, the control system transmits the impedance file to the communication buoy via a watertight data interface. Then, as... Figure 5 As shown, the control system activates the communication buoy release mechanism, and the communication buoy rises to the surface under its own buoyancy. After surfacing, the communication buoy automatically deploys its satellite communication terminal and transmits impedance data to the shore-based data center or the mother ship via satellite link.

[0109] In this embodiment, through the complete process of sensor deployment, data acquisition, preprocessing, and data transmission, autonomous detection of seabed magnetotelluric signals and near real-time data transmission are achieved, eliminating the traditional method's full dependence on the mother ship.

[0110] In one embodiment, prior to step S1, the seabed magnetotelluric detection method based on an autonomous mobile platform further includes:

[0111] S01: Obtain the preset task list, which includes the coordinates of multiple preset stations; understandably, the preset task list may also include the preset acquisition duration of each preset station, the migration path between each preset station, and the sensor deployment orientation parameters of each preset station.

[0112] Specifically, such as Figure 6 As shown, after the equipment installation and self-test are completed on the deck of the mother ship, the operator imports the preset work task list into the control system of the autonomous mobile platform through the shipboard control terminal. The self-test includes: checking the working status of the autonomous mobile platform's power module, navigation and positioning module, and underwater acoustic communication module; checking the operation of the deployment mechanism; checking the communication and storage functions of the data acquisition module and data preprocessing module; and checking the release mechanism of the communication mooring buoy and the satellite communication link, etc.

[0113] S02: Based on the coordinates of the current preset station to be measured, control the autonomous mobile platform to navigate to the preset station.

[0114] Specifically, after the device is deployed into the water, the autonomous mobile platform activates its power module and descends to the seabed based on initial positioning information. The surface-mounted USBL positioning array and the autonomous mobile platform's underwater acoustic communication module work together to track and locate the platform underwater. Based on the real-time position information from the navigation and positioning module and the coordinates of the target station in the preset task schedule, the autonomous mobile platform autonomously navigates to the target station using its maneuvering mechanism, with the positioning error controlled within a preset range (e.g., ±2 meters).

[0115] In one embodiment, after step S4, the seabed magnetotelluric detection method based on an autonomous mobile platform further includes:

[0116] S5: Control the deployment mechanism to retrieve the electric field sensor group and the magnetic field sensor group, and control the autonomous mobile platform to navigate to the next preset station according to the preset task list. Repeat steps S1 to S4 until all preset station tasks in the preset task list are completed.

[0117] Specifically, after the impedance of the current station is successfully transmitted back through the communication buoy (or after receiving a confirmation signal from the water surface receiver), the control system drives the deployment mechanism to work in reverse, retrieving both the electric field sensor group and the magnetic field sensor group to the platform body.

[0118] After all sensors confirm retrieval and lock, the control system reads the coordinates of the next preset station from the preset task schedule, drives the autonomous mobile platform to start its power module, and autonomously navigates to the next preset station. Upon reaching the next preset station, steps S1 to S4 are automatically repeated until all preset station tasks in the preset task schedule are completed.

[0119] After completing all pre-set station tasks, the autonomous mobile platform navigates to the pre-set recovery waiting area (such as the endpoint coordinates specified in the task schedule), maintains low-speed cruising or seabed standby mode, and awaits the acoustic wake-up command from the mother ship. Upon receiving the recovery command, the autonomous mobile platform surfaces (or waits for the mother ship to deploy the recovery cable), and the mother ship completes the salvage and recovery.

[0120] In this embodiment, a leapfrog operation mode of one-time deployment and multi-station autonomous measurement is realized through sensor recovery, station relocation and cyclic operation, which greatly reduces the mother ship operation time, reduces operation costs and dependence on weather and sea conditions.

[0121] In one embodiment, the electrode spacing formed after the electric field sensor array is deployed is greater than 10m;

[0122] The magnetic field sensor array was deployed and buried in seabed sediments.

[0123] Specifically, traditional seabed magnetotelluric receivers are limited by deck operating space and receiver cabin mechanical structure, resulting in electric field sensor electrode spacing typically only 8 to 10 meters and low signal-to-noise ratio (SNR) of the electric field signal. In this embodiment, after the autonomous mobile platform reaches the preset station, the electric field sensor array is deployed outside the platform body via a deployment mechanism, increasing the electric field sensor electrode spacing to over 100 meters, preferably 100 to 400 meters (more preferably 200 meters). The increased electrode spacing leads to a larger potential difference captured by the electric field sensors, thereby significantly improving the SNR of the electric field signal.

[0124] The magnetic field sensor assembly includes a triaxial inductive magnetic sensor and a triaxial fluxgate sensor. After the deployment mechanism pushes the magnetic field sensor assembly to a certain distance (e.g., 5m to 20m) from the platform body, the magnetic field sensor assembly is buried in the seabed sediment by the burial actuator, with the burial depth preferably being 0.3m to 0.5m.

[0125] The purpose of burying a magnetic field sensor in sediment is to: (1) isolate electromagnetic noise generated by seawater movement - the movement of seawater such as waves and ocean currents cutting the geomagnetic field will generate induced electromagnetic noise. Burying the magnetic field sensor in static sediment can remove it from the noise source of flowing water; (2) avoid interference from water flow mechanical vibration - sediment has viscosity, which can effectively absorb and isolate high-frequency micro-vibration interference brought by ocean currents; (3) provide a constant temperature and humidity environment to improve the stability of the magnetic field baseline; (4) ensure the long-term stability of physical attitude and ensure that the three-axis pointing is accurate and remains unchanged for a long time.

[0126] In this embodiment, the electrode spacing of the electric field sensor is extended from the traditional 10m to more than 100m, the signal strength is increased by more than 10 times, and the electric field signal-to-noise ratio is greatly improved; the magnetic field sensor is buried in the sediment, which effectively isolates the noise of seawater movement and electromagnetic interference from the platform, and the magnetic field signal-to-noise ratio is significantly improved.

[0127] In one embodiment, the electric field sensor group includes several electric field sensors arranged in mutually perpendicular directions to form two sets of orthogonal electric field measurement lines; the mutually perpendicular directions are controlled within a preset angle range by a laser positioning device.

[0128] The electric field sensor array consists of four electric field sensors, arranged along four mutually perpendicular directions (e.g., north, south, east, and west). The electric field sensor pairs in the north and south directions form the first electric field measurement line (Ex), and the electric field sensor pairs in the east and west directions form the second electric field measurement line (Ey). The two sets of measurement lines are orthogonal to each other. The arrangement distance in each direction is the same (e.g., 100m), so that the center point is located at the geometric center of the four electric field sensors.

[0129] The deployment mechanism integrates a laser positioning device. During the deployment of the electric field sensor, the laser positioning device measures the deployment direction in real time, ensuring that the included angles of each direction are within a preset angle range (e.g., 90°±2°), and that the parallelism / perpendicularity error with the preset survey line direction is within allowable limits. The laser positioning device can achieve high-precision orientation underwater, overcoming the problem of large orientation errors caused by reliance on manual deployment in traditional methods.

[0130] In this embodiment, the two sets of orthogonally arranged electric field survey lines meet the theoretical requirements of the magnetotelluric sounding method for orthogonal measurement of electric field components (Ex, Ey); the laser positioning device achieves high-precision underwater orientation, ensuring the accuracy of the layout orientation and improving the reliability of the measurement data.

[0131] In one embodiment, two sets of redundant electric field sensors are deployed in each direction.

[0132] Two redundant electric field sensors are deployed in each of the following directions (north, south, east, and west) (i.e., two electric field sensors in each direction, for a total of eight electric field sensors). Under normal measurement conditions, the first set of electric field sensors is used to acquire signals; when an abnormal signal is detected in a certain set of electric field sensors, the data acquisition module automatically switches to the redundant electric field sensor pair in the same direction for measurement.

[0133] The redundancy switching judgment logic is as follows: the data acquisition module monitors the signal quality parameters (including signal amplitude, range drift rate, contact resistance, etc.) of each electric field sensor pair in real time. When a parameter exceeds the preset threshold, the electric field sensor group is determined to be faulty and switching is automatically performed.

[0134] In this embodiment, the deployment of redundant electric field sensors improves the reliability of observation data. When a group of electric field sensors fails due to complex seabed environment (such as sediment cover, biological attachment, cable damage, etc.), the system can automatically switch to redundant electric field sensors to continue measurement, avoiding the risk of the entire station's data being invalidated due to the failure of a single electric field sensor.

[0135] In one embodiment, before the data acquisition module is started, the system further includes: controlling the power module, navigation module, and underwater acoustic communication module of the autonomous mobile platform to shut down or enter a low-power standby state.

[0136] Specifically, after the electric field sensor group and magnetic field sensor group are deployed and before data acquisition begins, the control system shuts down the autonomous mobile platform's power module (thruster / track drive motor), navigation module (inertial navigation, Doppler velocimeter, etc.), and underwater acoustic communication module, putting it into a low-power silent state. This is because the power module, navigation module, and underwater acoustic communication module generate electromagnetic noise during operation (such as electromagnetic radiation generated by motor rotation and acoustic signals emitted by underwater acoustic communication). This noise can be conducted to the sensors through the water or platform structure, interfering with the measurement of the geomagnetic signal.

[0137] Before the data acquisition module is started, the following steps are also taken: in-situ calibration of the electric field sensor group and the magnetic field sensor group after they are deployed.

[0138] Specifically, after shutting down the interference source module, the control system performs in-situ calibration of the electric field sensor group and the magnetic field sensor group, including zero drift calibration, gain calibration, and orientation calibration. In-situ calibration refers to calibration performed in the actual field environment where the sensors are deployed on the seabed. This can eliminate zero-point and gain drift generated during the transportation, deployment, and arrangement of the sensors, ensuring the measurement accuracy of the sensors in the seabed environment.

[0139] In this embodiment, by shutting down the platform's power, navigation, and communication modules, the interference of the platform's own electromagnetic noise on the magnetotelluric signal measurement is eliminated, thus improving data quality; and by conducting in-situ calibration, the drift generated by the sensor during deployment is eliminated, thus improving measurement accuracy.

[0140] The seabed magnetotelluric detection method and device based on an autonomous mobile platform provided in this application are mainly aimed at the application field of deep seabed structure detection.

[0141] This application addresses the pain points of current detection methods and instruments, and leverages the advantages of underwater autonomous mobile platforms to propose a seabed magnetotelluric detection method and device based on an autonomous mobile platform. To address the issue of short electrode spacing and low electric field signal-to-noise ratio in current instruments, an autonomous wiring structure for the seabed autonomous mobile platform is proposed, increasing the electrode spacing from the existing 10m to at least 100m, significantly improving the electric field signal-to-noise ratio. To address the electromagnetic compatibility issues of existing magnetic sensors, a magnetic field sensor deployment mechanism for the seabed autonomous mobile platform is proposed, enabling the magnetic field sensor to be located away from the platform itself and buried in seabed sediments, thus avoiding interference from moving seawater and the electromagnetic noise of the mobile platform itself, significantly improving the magnetic field signal-to-noise ratio. The autonomous mobile platform autonomously moves the survey line, and after reaching the preset station, autonomously completes sensor deployment and initiates data acquisition. After observation, it autonomously moves to the next station without intervention from the mother ship. The magnetotelluric detection payload autonomously completes data preprocessing and transmits the data back to the shore station via a communication buoy, significantly improving data real-time performance.

[0142] Compared with the prior art, the present invention has the following advantages:

[0143] The electric field data has a high signal-to-noise ratio. With the help of the electric field sensor deployment mechanism, the electric field sensor can be precisely deployed, and the electrode spacing can be extended from the existing 10m to at least 100m, which greatly improves the signal-to-noise ratio.

[0144] The magnetic field data has a high signal-to-noise ratio. With the help of the magnetic field sensor deployment mechanism, it is buried in the sediment, softly connected to the body, and far away from the platform body, eliminating electromagnetic compatibility risks and improving the signal-to-noise ratio of magnetic field observation.

[0145] It has high operational efficiency, can complete multi-station measurements autonomously with a single deployment, and does not require the accompaniment of a work vessel, thus reducing reliance on ship time.

[0146] With strong environmental adaptability, the platform is located on the seabed and autonomously completes measurements, unaffected by severe weather and sea conditions, thus enhancing its environmental adaptability.

[0147] The data is highly real-time. After data collection at a single station is completed, data preprocessing is performed, and the underwater glider data is transmitted back to the shore station, achieving near real-time data transmission.

[0148] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for seabed magnetotelluric detection based on an autonomous mobile platform, characterized in that, The autonomous mobile platform, equipped with a magnetotelluric detection payload, includes the following steps: S1: At the preset station, control the deployment mechanism installed on the autonomous mobile platform to deploy the electric field sensor group and magnetic field sensor group in the magnetotelluric detection payload outside the autonomous mobile platform body respectively. S2: After the electric field sensor group and the magnetic field sensor group are deployed, the raw time series data sent by the data acquisition module is received. The raw time series data is obtained by the data acquisition module from sampling and quantizing the seabed magnetotelluric signal. The seabed magnetotelluric signal is acquired by the deployed electric field sensor group and the magnetic field sensor group. S3: Preprocess the original time series data to obtain impedance results, where the amount of impedance data is much smaller than the amount of original time series data. S4: Transmit the impedance to the communication buoy mounted on the autonomous mobile platform, and control the communication buoy to rise to the surface of the water, and send the impedance to the surface receiver.

2. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 1, characterized in that, Before step S1, the following are also included: S01: Obtain a preset task list, which includes the coordinates of multiple preset stations; S02: Based on the coordinates of the preset station to be measured, control the autonomous mobile platform to navigate to the preset station.

3. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 2, characterized in that, After step S4, the following also includes: S5: Control the deployment mechanism to retrieve the electric field sensor group and the magnetic field sensor group, and control the autonomous mobile platform to navigate to the next preset station according to the preset task list, repeat steps S1 to S4 until all preset station tasks in the preset task list are completed.

4. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 1, characterized in that, The electrode spacing formed after the electric field sensor group is deployed is greater than 10m. The magnetic field sensor array was laid out in the seabed sediments according to the expected direction.

5. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 1, characterized in that, The electric field sensor group includes several electric field sensors, which are arranged in mutually perpendicular directions to form two sets of orthogonal electric field measurement lines. The mutually perpendicular directions are controlled within a preset angle range by a laser positioning device.

6. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 5, characterized in that, Two sets of redundant electric field sensors are deployed in each direction.

7. The seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 1, characterized in that, Before the data acquisition module is started, the system also includes: controlling the power module, navigation module and underwater acoustic communication module of the autonomous mobile platform to shut down or enter a low-power standby state; The electric field sensor group and the magnetic field sensor group were calibrated in situ after being deployed and placed.

8. An apparatus for use in the seabed magnetotelluric detection method based on an autonomous mobile platform as described in any one of claims 1 to 7, characterized in that, The device includes: The magnetotelluric detection payload includes: an electric field sensor group, a magnetic field sensor group, a data acquisition module, and a data preprocessing module. The electric field sensor group and the magnetic field sensor group are used to collect seabed magnetotelluric signals; The data acquisition module is electrically connected to the electric field sensor group and the magnetic field sensor group, and is configured to perform equal-interval sampling and quantization of the seabed magnetotelluric signal after the electric field sensor group and the magnetic field sensor group are deployed and in place, so as to obtain the original time series data. The data preprocessing module is communicatively connected to the data acquisition module and is configured to preprocess the original time series data to obtain impedance results, wherein the amount of impedance data is much smaller than the amount of original time series data. An autonomous mobile platform is equipped with the magnetotelluric detection payload; the autonomous mobile platform includes: a platform body, a deployment mechanism, a communication mooring, and a control system, wherein the deployment mechanism, the communication mooring, and the control system are all mounted on the platform body; The deployment mechanism is mechanically connected to the electric field sensor group and the magnetic field sensor group, and is configured to deploy the electric field sensor group and the magnetic field sensor group outside the autonomous mobile platform body after reaching the preset station. The communication buoy is communicatively connected to the data preprocessing module, configured to receive the impedance, and can be released to float to the surface and send the impedance to the surface receiver. The control system is connected to the autonomous mobile platform, the deployment mechanism, the data acquisition module, the data preprocessing module, and the communication buoy control, and is configured to execute the method steps as described in any one of claims 1 to 7.

9. The apparatus for a seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 8, characterized in that, The deployment mechanism includes a laser positioning device, which is installed on the platform body and is used to measure the deployment direction during the deployment of the electric field sensor group and the magnetic field sensor group to ensure that the included angle of each direction is within a preset angle range.

10. The apparatus for a seabed magnetotelluric detection method based on an autonomous mobile platform as described in claim 8, characterized in that, The autonomous mobile platform also includes an underwater acoustic communication module, a navigation and positioning module, an energy and power module, and a motor mechanism; The underwater acoustic communication module is used to communicate with the surface-mounted USBL positioning array to achieve underwater positioning and tracking of the autonomous mobile platform. The navigation and positioning module includes an inertial navigation unit and / or a Doppler velocimeter, used to provide real-time position and heading information in an underwater environment without satellite signals; The energy power module includes a battery pack, which is used to power the autonomous mobile platform and the magnetotelluric detection payload. The motor mechanism includes a propeller or a tracked walking mechanism, used to drive the autonomous mobile platform to navigate in water or walk on the seabed.

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