A method and system for detecting oil spill thickness at sea based on an underwater autonomous vehicle

Abstract

The application relates to the technical field of offshore oil spill detection, and discloses a kind of offshore oil spill thickness detection method and system based on underwater autonomous vehicle, system includes the control unit in underwater vehicle, the control unit is respectively with ultrasonic signal transceiver unit, ultrasonic signal processing and storage unit, positioning and navigation unit, path planning unit, autonomous obstacle avoidance unit and underwater acoustic communication unit electric connection;Autonomous obstacle avoidance unit carries out active detection;Underwater acoustic communication unit sends trajectory above sea surface oil spill thickness measurement result to command center;And receive instruction information;Path planning unit plans optimal motion path;Navigation positioning unit is used for underwater position positioning;Control unit is used for motion control and depth control;Ultrasonic signal transceiver unit carries out ultrasonic signal emission and reception.The application carries out real-time continuous measurement to the thickness of oil spill layer in a wide range, multiple dispersed areas through underwater autonomous vehicle, efficiently plans detection route, improves detection efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore oil spill detection, and in particular to a method and system for detecting offshore oil spill thickness based on an underwater autonomous vehicle. Background Art

[0002] With the increasing exploitation of deep-sea oil and gas resources and the growing reliance on offshore crude oil transportation in my country, the risk of marine oil spills is increasing year by year. In recent years, my country has experienced an average of approximately 500 major and minor marine oil spills annually, including the ConocoPhillips oil rig leak in the Bohai Sea and the Dalian oil pipeline explosion. The task of preventing and controlling marine oil pollution is urgent. Regardless of the method used to deal with marine oil spills, timely and accurate information on the oil spill thickness is crucial for effective and efficient management. Therefore, efficient and precise measurement of oil spill thickness is a key research topic in this field.

[0003] Currently, extensive theoretical and experimental research has been conducted both domestically and internationally on oil spill thickness detection technologies, primarily using ultraviolet and infrared hyperspectral analysis, microwave radiometers, satellite and airborne synthetic aperture radars, buoys, and antenna resistance. However, these technical experiments have mostly been conducted under relatively ideal conditions and all have limitations. For example, ultraviolet and infrared hyperspectral analysis is only effective for measuring the thickness of thin oil films (<1 mm) and is susceptible to interference from solar flares and marine life. Buoy technology is only suitable for fixed-point measurements. Microwave radiometers are easily affected by factors such as waves and solar radiation, significantly reducing measurement accuracy. Therefore, existing technologies are unable to meet the needs of marine oil pollution monitoring. Real-time, online, and continuous on-site marine oil pollution monitoring is a pressing technical challenge facing my country and the world. Therefore, developing a practical, real-time, efficient, and large-scale oil spill thickness detection method and corresponding detection system is a significant need. Summary of the Invention

[0004] In order to overcome or alleviate one or more of the above technical problems, the present invention aims to provide a method and system for detecting the thickness of offshore oil spills based on an underwater autonomous vehicle, which has the capability of real-time online, efficient and large-scale automatic measurement of the thickness of the oil spill layer.

[0005] The present invention provides the following technical solutions:

[0006] In one aspect, the present invention provides a marine oil spill thickness detection system based on an underwater autonomous vehicle, comprising: a control unit disposed in the underwater vehicle, the control unit being electrically connected to an ultrasonic signal transceiver unit, an ultrasonic signal processing and storage unit, a positioning and navigation unit, a path planning unit, an autonomous obstacle avoidance unit, and an underwater acoustic communication unit;

[0007] The autonomous obstacle avoidance unit is configured to actively detect the area ahead of the underwater vehicle, output the detection results in the form of a two-dimensional image, and use a deep learning network to autonomously and intelligently identify obstacles in the two-dimensional image, and send the identification results to the control unit;

[0008] The underwater acoustic communication unit is used to send the underwater vehicle's remaining power information, movement trajectory information, and the measurement results of the oil spill thickness on the sea surface above the trajectory to the command center for display at fixed intervals; and to receive real-time instructions from the command center regarding the area to be detected in the next stage;

[0009] The path planning unit is used to plan the next optimal movement path of the underwater vehicle based on the position information in the instruction information of the next stage of the detection area received by the underwater acoustic communication unit and the current position information of the underwater vehicle recorded by the navigation and positioning unit, and send it to the control unit;

[0010] The navigation and positioning unit is used to locate the underwater position of the underwater vehicle, record the motion trajectory information of the underwater vehicle in real time, and send the motion trajectory information to the command center for display through the underwater acoustic communication unit;

[0011] The control unit is used to perform motion control based on the position information sent by the navigation and positioning unit, the motion path sent by the path planning unit, and the obstacle information sent by the autonomous obstacle avoidance unit; and to control the depth-fixed motion of the underwater vehicle; and to control the ultrasonic signal transceiver unit to transmit and receive ultrasonic signals;

[0012] The ultrasonic signal transceiver unit is used to transmit and receive ultrasonic signals according to the instructions of the control unit, and send the collected digital signals to the ultrasonic signal processing and storage unit in real time;

[0013] The ultrasonic signal processing and storage unit is used to analyze the digital signal sent by the ultrasonic signal transceiver unit using an ultrasonic signal processing algorithm, calculate the oil spill thickness, record the digital signal sent by the ultrasonic signal transceiver unit, and record the oil spill thickness information and corresponding time information, and send the information to the control unit at the same time.

[0014] According to some embodiments, the ultrasonic signal transceiver unit is provided with an ultrasonic probe, which is a water-immersible broadband ultrasonic probe, adopts a multiple ultrasonic probe deployment mode, and has an operating center frequency of 0.5MHz to 7.5MHz.

[0015] According to some embodiments, the ultrasound signal transceiver unit and the ultrasound probe adopt a co-located transceiver working mode.

[0016] According to some embodiments, the ultrasound signal transceiver unit and the ultrasound probe adopt a serial sequential transmission mode or a parallel synchronous transmission mode.

[0017] According to some embodiments, during the oil spill thickness measurement process, the underwater vehicle is positioned at a depth of 1.5 m to 3 m below the water surface.

[0018] According to some embodiments, the underwater acoustic communication unit adopts full-duplex underwater acoustic communication.

[0019] On the other hand, the present invention also provides a detection method of the marine oil spill thickness detection system based on the underwater autonomous vehicle as described above, which comprises the following steps:

[0020] S1: The command center plans the movement trajectory of the underwater vehicle based on the information of the oil spill area that has been explored. The command center loads the trajectory information into the control unit of the underwater vehicle, and the underwater vehicle starts the navigation mode after launching;

[0021] S2: The control unit controls the underwater vehicle to move to the oil spill area based on the position information provided by the navigation and positioning unit and the loaded motion trajectory information. At the same time, the autonomous obstacle avoidance unit provides the control unit with information about obstacles ahead of the underwater vehicle to ensure the safety of the underwater vehicle during navigation.

[0022] S3: After the underwater vehicle reaches the starting point of the oil spill area, the control unit starts the ultrasonic signal transceiver unit and the ultrasonic signal processing and storage unit. The ultrasonic signal processing and storage unit calculates the oil spill thickness information and the location information of the detection point in real time, and stores the above thickness and location information and the ultrasonic time domain echo signal;

[0023] S4: The underwater vehicle moves back and forth in a zigzag or S-shaped trajectory within the oil spill area, and transmits the detected oil spill thickness information, corresponding location information, and battery remaining information to the command center at regular intervals. The command center sends control instructions to the control unit via the underwater acoustic communication unit, including navigation speed, ultrasonic pulse transmission frequency, and whether to proceed to a new oil spill area for detection;

[0024] S5: After the underwater vehicle completes loading the motion trajectory in step S1, if the control unit receives an instruction that it does not need to proceed to a new oil spill area for detection, it proceeds to step S6; if the control unit receives an instruction that it needs to proceed to a new oil spill area for detection, it proceeds to step S7:

[0025] S6: The underwater vehicle returns to its starting position autonomously;

[0026] S7: The path planning unit plans the optimal motion trajectory according to the current position of the underwater vehicle and the target area position information, and sends it to the control unit to move the underwater vehicle to the new oil spill area, and returns to step S3.

[0027] According to some embodiments, step S3 comprises the following steps:

[0028] S31: The control unit controls the ultrasonic signal transceiver unit to start measurement, and simultaneously measures the thickness of the oil spill on the sea surface above the motion trajectory in real time;

[0029] S32: The ultrasonic probe transmits the ultrasonic signal stimulated by the ultrasonic signal transceiver unit toward the sea surface, and receives the ultrasonic signal reflected from the oil layer and water reflection surface and the oil layer and air reflection surface. At the same time, the ultrasonic signal transceiver unit records the current time information and sends the digitized ultrasonic reflection signal and the corresponding time information to the ultrasonic signal processing and storage unit;

[0030] S33: The ultrasonic signal processing and storage unit analyzes the ultrasonic reflection signal using an ultrasonic signal processing algorithm, extracts the round-trip propagation time of the ultrasonic wave between the oil layer and the water reflection surface and between the oil layer and the air reflection surface, and obtains the thickness of the oil layer based on the propagation time; records the digital signal sent by the ultrasonic signal transceiver unit, the oil spill thickness information, and the corresponding time information, and simultaneously sends the thickness and time information to the control unit;

[0031] S34: At fixed intervals, the control unit sends the oil layer thickness and corresponding time information measured by the ultrasonic signal processing and storage unit, the position and corresponding time information measured by the positioning and navigation unit, and the battery remaining information to the underwater acoustic communication unit, and then sends it to the command center through the wireless communication method of the underwater acoustic communication unit.

[0032] According to some embodiments, the ultrasound signal processing algorithm in step S33 adopts a first-order correlation method, comprising the following steps:

[0033] S331: using two time windows to extract the reflection signals of the oil layer and the water reflection surface and the oil layer and the air reflection surface respectively;

[0034] S332: Perform a correlation operation on the two channel signals. The peak point corresponding to the correlation function is the time delay between the two reflected signals, that is, the round-trip propagation time τ;

[0035] S333: According to the round-trip propagation time τ, the thickness of the oil layer is obtained, that is:

[0036] THK=c×τ2

[0037] Where c is the propagation speed of ultrasound in the oil spill layer.

[0038] According to some embodiments, in step S3, for the oil spill thickness measurement result at each measurement point, a method of averaging multiple measurements is used to eliminate abnormal measurement values.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The method and system for detecting the thickness of an offshore oil spill based on an autonomous underwater vehicle provided by the present invention utilizes an underwater vehicle that can be remotely and automatically controlled to perform real-time, high-precision, efficient, and large-scale continuous measurement of the thickness of the oil spill layer in multiple dispersed areas. The control unit controls various functional modules, such as wirelessly receiving instructions from a command center through an underwater acoustic communication unit and feeding back the real-time position of the underwater vehicle to the command center through a navigation and positioning unit. Furthermore, the path planning unit can efficiently plan detection routes, thereby improving detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A flow chart of a method for detecting the thickness of an offshore oil spill based on an underwater autonomous vehicle is provided in an embodiment of the present invention.

[0042] Figure 2 This is a structural block diagram of a marine oil spill thickness detection system based on an underwater autonomous vehicle provided in an embodiment of the present invention.

[0043] Figure 3 A schematic diagram of the motion trajectory of an underwater autonomous vehicle in an oil spill area provided by an embodiment of the present invention.

[0044] Figure 4 Schematic diagram of ultrasonic reflection signals collected by the ultrasonic signal transceiver unit provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0045] The present invention is described in detail below with reference to the embodiments and accompanying drawings. However, it should be understood that the embodiments and accompanying drawings are merely exemplary descriptions of the present invention and do not constitute any limitation on the scope of protection of the present invention. All reasonable variations and combinations within the scope of the inventive concept of the present invention fall within the scope of protection of the present invention.

[0046] The present invention will be further described below with reference to the accompanying drawings.

[0047] Example 1

[0048] like Figure 1 This embodiment provides a method for detecting the thickness of an offshore oil spill based on an underwater autonomous vehicle. The specific process of the detection method is as follows:

[0049] S1: The movement trajectory of the autonomous underwater vehicle is planned based on the information of the oil spill area that has been explored by the command center. The command center loads the trajectory information into the control unit of the underwater vehicle, and the underwater vehicle starts the navigation mode after launching;

[0050] S2: The control unit controls the underwater vehicle to move to the oil spill area based on the position information provided by the navigation and positioning unit and the loaded motion trajectory information. At the same time, the autonomous obstacle avoidance unit provides the control unit with information about obstacles ahead of the underwater vehicle to ensure the safety of the underwater vehicle during navigation.

[0051] S3: After the underwater vehicle reaches the starting point of the oil spill area, the control unit starts the ultrasonic signal transceiver unit and the ultrasonic signal processing and storage unit. The ultrasonic signal processing and storage unit calculates the oil spill thickness information and the position information of the detection point in real time, and stores the above thickness and position information and the ultrasonic time domain echo signal; the ultrasonic time domain echo signal is in the form of Figure 4 For the oil spill thickness measurement results at each measurement point, the method of averaging multiple measurements is used to eliminate abnormal measurement values, which are caused by factors such as waves and vehicle roll.

[0052] S4: The motion trajectory of the underwater vehicle in the oil spill area is a Z-shaped or S-shaped reciprocating motion. The specific motion trajectory is as follows: Figure 3 As shown, the detected oil spill thickness information, corresponding location information, and battery remaining information are sent to the command center at regular intervals (the command center can adjust the time interval through the underwater acoustic communication unit); the command center sends control instructions to the control unit of the underwater vehicle through the underwater acoustic communication unit, including navigation speed, ultrasonic pulse emission frequency, and whether to proceed to a new oil spill area for detection;

[0053] S5: After the underwater vehicle completes loading the motion trajectory in step S1, if the control unit receives an instruction that it does not need to proceed to a new oil spill area for detection, it proceeds to step S6; if the control unit receives an instruction that it needs to proceed to a new oil spill area for detection, it proceeds to step S7:

[0054] S6: The underwater vehicle autonomously returns to its starting position and can be salvaged;

[0055] S7: The path planning unit plans the optimal motion trajectory according to the current position of the underwater vehicle and the target area position information, and sends it to the control unit to move the underwater vehicle to the new oil spill area, and returns to step S3.

[0056] More specifically, step S3 includes the following steps:

[0057] S31: The control unit controls the ultrasonic signal transceiver unit to start measurement, and simultaneously measures the thickness of the oil spill on the sea surface above the motion trajectory in real time;

[0058] S32: The ultrasonic probe transmits the ultrasonic signal stimulated by the ultrasonic signal transceiver unit toward the sea surface, and receives the ultrasonic signal reflected from the oil layer and water reflection surface and the oil layer and air reflection surface. At the same time, the ultrasonic signal transceiver unit records the current time information and sends the digitized ultrasonic reflection signal and the corresponding time information to the ultrasonic signal processing and storage unit;

[0059] S33: The ultrasonic signal processing and storage unit analyzes the ultrasonic reflection signal using an ultrasonic signal processing algorithm, extracts the round-trip propagation time of the ultrasonic wave between the oil layer and the water reflection surface and between the oil layer and the air reflection surface, and obtains the thickness of the oil layer based on the propagation time; records the digital signal sent by the ultrasonic signal transceiver unit, the oil spill thickness information, and the corresponding time information, and simultaneously sends the thickness and time information to the control unit;

[0060] S34: At regular intervals, the control unit transmits the oil layer thickness and corresponding time information measured by the ultrasonic signal processing and storage unit, the position and corresponding time information measured by the positioning and navigation unit, and the battery remaining information to the underwater acoustic communication unit, and then transmits the information to the command center via wireless communication of the underwater acoustic communication unit;

[0061] The ultrasonic signal processing algorithm in step S33 adopts a first-order correlation method, specifically:

[0062] The ultrasonic signal processing algorithm adopts the first-order correlation method, which specifically includes the following steps:

[0063] S331: using two time windows to extract the reflection signals of the oil layer and the water reflection surface and the oil layer and the air reflection surface respectively;

[0064] S332: Perform a correlation operation on the two channel signals. The peak point corresponding to the correlation function is the time delay between the two reflected signals, that is, the round-trip propagation time τ;

[0065] S333: According to the round-trip propagation time τ, the thickness of the oil layer is obtained, that is:

[0066] THK=c×τ2

[0067] Where c is the propagation speed of ultrasound in the oil spill layer.

[0068] If the command center issues a new measurement area, step S2 includes the following steps:

[0069] S21: The command center sends the location information of the new measurement area to the underwater acoustic communication unit through underwater acoustic wireless communication. The path planning unit plans the motion path according to the area location information reported by the underwater acoustic communication unit and sends it to the control unit;

[0070] S22: The control unit controls the motion of the underwater vehicle according to the position information sent by the navigation and positioning unit, the motion path sent by the path planning unit, and the obstacle information sent by the autonomous obstacle avoidance unit.

[0071] When all measurement areas have been measured, the command center will draw an oil layer thickness distribution map of the entire oil spill coverage area based on the underwater vehicle motion trajectory information and oil spill thickness information received.

[0072] Example 2

[0073] like Figure 2 This embodiment provides a marine oil spill thickness detection system based on an underwater autonomous vehicle. The detection system includes an underwater vehicle, a navigation and positioning unit, a control unit, a path planning unit, an ultrasonic signal transceiver unit, an ultrasonic signal processing and storage unit, an underwater acoustic communication unit, and an autonomous obstacle avoidance unit. The control unit is electrically connected to the navigation and positioning unit, the path planning unit, the ultrasonic signal transceiver unit, the ultrasonic signal processing and storage unit, the underwater acoustic communication unit, and the autonomous obstacle avoidance unit, respectively. The ultrasonic signal processing and storage unit is electrically connected to the ultrasonic signal transceiver unit, and the ultrasonic signal transceiver unit is electrically connected to several ultrasonic probes. The navigation and positioning unit is electrically connected to the path planning unit and the underwater acoustic communication unit, respectively, and the path planning unit is electrically connected to the autonomous obstacle avoidance unit.

[0074] All units are integrated in the underwater vehicle, which can conduct large-scale and autonomous measurements of oil spills at sea; and exchange commands and information with the command center through underwater acoustic wireless communication.

[0075] Specifically:

[0076] The autonomous obstacle avoidance unit uses a two-dimensional forward-looking sonar to actively detect obstacles within 100 meters ahead of the underwater vehicle. The detection results are output as two-dimensional images. A deep learning network is used to autonomously and intelligently identify obstacles in the two-dimensional images and send the identification results to the control unit.

[0077] The underwater acoustic communication unit uses a full-duplex underwater acoustic communication device to send the underwater vehicle's remaining power information, movement trajectory information, and oil spill thickness measurement results above the trajectory to the command center for display at fixed intervals; and receive real-time instructions from the command center regarding the area to be detected in the next phase;

[0078] The path planning unit plans the next optimal movement path of the underwater vehicle based on the position information of the area to be detected in the next stage received by the underwater acoustic communication unit and the current position information of the underwater vehicle recorded by the positioning and navigation unit, and sends it to the control unit;

[0079] The navigation positioning unit is a combination of a Doppler velocity meter and an ultra-short baseline acoustic positioning device, which is used for high-precision underwater positioning of the underwater vehicle and real-time recording of the motion trajectory information of the underwater vehicle, and the motion trajectory information is sent to the command center through the underwater acoustic communication unit for display.

[0080] The control unit is used for motion control according to the position information sent by the navigation positioning unit, the motion path sent by the path planning unit, and the obstacle information sent by the autonomous obstacle avoidance unit, and realizes depth control of the underwater vehicle; and the ultrasonic signal transmitting and receiving unit is controlled to transmit and receive ultrasonic signals.

[0081] The ultrasonic signal transmitting and receiving unit realizes ultrasonic signal transmission and reception according to the control unit instructions; wherein the signal transmission includes ultrasonic signal generation, amplification and excitation functions; the signal reception mainly includes filtering, amplification and acquisition functions; and the collected digital signals are sent to the ultrasonic signal processing and storage unit in real time.

[0082] The ultrasonic signal processing and storage unit uses an ultrasonic signal processing algorithm to analyze the digital signals sent by the ultrasonic signal transmitting and receiving unit, calculates the oil spill thickness, records the digital signals sent by the ultrasonic signal transmitting and receiving unit, records the oil spill thickness information and corresponding time information, and sends the information to the control unit.

[0083] The ultrasonic probe is a water-immersed ultrasonic probe, and a plurality of ultrasonic probes are arranged in a mode, and the working center frequency is 0.5MHz-7.5MHz.

[0084] One channel of the ultrasonic signal transmitting and receiving unit is connected with one ultrasonic probe through a cable, and the ultrasonic signal transmitting and receiving unit and the ultrasonic probe both adopt a transceiving co-located working mode.

[0085] The ultrasonic signal transmitting and receiving unit and the ultrasonic probe both can adopt a serial transmission mode or a parallel synchronous transmission mode.

[0086] During the oil spill thickness measurement process, the underwater vehicle is kept at a depth of 1.5m-3m below the water surface.

[0087] For the oil spill thickness measurement result of each measurement point, a multiple measurement and averaging method is used to eliminate abnormal measurement values caused by sea waves and vehicle rolling and the like.

[0088] The above embodiments are only preferred embodiments of the present application, and the protection scope of the present application is not limited to the above embodiments. Any technical solution falling within the concept of the present application shall fall within the protection scope of the present application. It should be noted that improvements and refinements made by ordinary skilled persons in the art without departing from the principles of the present application shall also be considered as falling within the protection scope of the present application.

Claims

1. A marine oil spill thickness detection system based on an underwater autonomous vehicle, characterized in that: include: A control unit is provided in the underwater vehicle, wherein the control unit is electrically connected to the ultrasonic signal transceiver unit, the ultrasonic signal processing and storage unit, the positioning and navigation unit, the path planning unit, the autonomous obstacle avoidance unit, and the underwater acoustic communication unit; The autonomous obstacle avoidance unit is configured to actively detect the area ahead of the underwater vehicle, output the detection results in the form of a two-dimensional image, and use a deep learning network to autonomously and intelligently identify obstacles in the two-dimensional image, and send the identification results to the control unit; The underwater acoustic communication unit is used to send the remaining power information, movement trajectory information and the measurement results of the oil spill thickness on the sea surface above the trajectory of the underwater vehicle to the command center for display at fixed intervals; And receive real-time instructions from the command center about the areas that need to be detected in the next stage; The path planning unit is used to plan the next optimal movement path of the underwater vehicle based on the position information in the instruction information of the next stage of the detection area received by the underwater acoustic communication unit and the current position information of the underwater vehicle recorded by the navigation and positioning unit, and send it to the control unit; The navigation and positioning unit is used to locate the underwater position of the underwater vehicle, record the motion trajectory information of the underwater vehicle in real time, and send the motion trajectory information to the command center for display through the underwater acoustic communication unit; The control unit is used to perform motion control based on the position information sent by the navigation and positioning unit, the motion path sent by the path planning unit, and the obstacle information sent by the autonomous obstacle avoidance unit; and to control the depth-fixed motion of the underwater vehicle; and to control the ultrasonic signal transceiver unit to transmit and receive ultrasonic signals; The ultrasonic signal transceiver unit is used to transmit and receive ultrasonic signals according to the instructions of the control unit, and send the collected digital signals to the ultrasonic signal processing and storage unit in real time; The ultrasonic signal processing and storage unit is used to analyze the digital signal sent by the ultrasonic signal transceiver unit using an ultrasonic signal processing algorithm, calculate the oil spill thickness, record the digital signal sent by the ultrasonic signal transceiver unit, record the oil spill thickness information and the corresponding time information, and send the information to the control unit at the same time.

2. The marine oil spill thickness detection system based on underwater autonomous vehicles according to claim 1 is characterized in that: The ultrasonic signal transceiver unit is provided with an ultrasonic probe, which is a water-immersed broadband ultrasonic probe. A multiple ultrasonic probe deployment mode is adopted, and the operating center frequency thereof is 0.5 MHz to 7.5 MHz.

3. The marine oil spill thickness detection system based on underwater autonomous vehicle according to claim 2 is characterized in that: The ultrasonic signal transceiver unit and the ultrasonic probe adopt a co-located transceiver working mode.

4. The marine oil spill thickness detection system based on underwater autonomous vehicle according to claim 2 is characterized in that: The ultrasonic signal transceiver unit and the ultrasonic probe adopt a serial sequential transmission mode or a parallel synchronous transmission mode.

5. The marine oil spill thickness detection system based on underwater autonomous vehicle according to claim 1 is characterized in that: During the oil spill thickness measurement process, the underwater vehicle is set at a depth of 1.5m to 3m below the water surface.

6. The marine oil spill thickness detection system based on underwater autonomous vehicle according to claim 1 is characterized in that: The underwater acoustic communication unit adopts full-duplex underwater acoustic communication.

7. A method for detecting the thickness of an offshore oil spill based on an underwater autonomous vehicle according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1: The command center plans the movement trajectory of the underwater vehicle based on the information of the oil spill area that has been explored. The command center loads the trajectory information into the control unit of the underwater vehicle, and the underwater vehicle starts the navigation mode after launching; S2: The control unit controls the underwater vehicle to move to the oil spill area based on the position information provided by the navigation and positioning unit and the loaded motion trajectory information. At the same time, the autonomous obstacle avoidance unit provides the control unit with information about obstacles ahead of the underwater vehicle to ensure the safety of the underwater vehicle during navigation. S3: After the underwater vehicle reaches the starting point of the oil spill area, the control unit starts the ultrasonic signal transceiver unit and the ultrasonic signal processing and storage unit. The ultrasonic signal processing and storage unit calculates the oil spill thickness information and the location information of the detection point in real time, and stores the above thickness and location information and the ultrasonic time domain echo signal; S4: The underwater vehicle moves back and forth in a zigzag or S-shaped trajectory within the oil spill area, and transmits the detected oil spill thickness information, corresponding location information, and battery remaining information to the command center at regular intervals. The command center sends control instructions to the control unit via the underwater acoustic communication unit, including navigation speed, ultrasonic pulse transmission frequency, and whether to proceed to a new oil spill area for detection; S5: After the underwater vehicle completes loading the motion trajectory in step S1, if the control unit receives an instruction that it does not need to proceed to a new oil spill area for detection, it proceeds to step S6; if the control unit receives an instruction that it needs to proceed to a new oil spill area for detection, it proceeds to step S7: S6: The underwater vehicle returns to its starting position autonomously; S7: The path planning unit plans the optimal motion trajectory according to the current position of the underwater vehicle and the target area position information, and sends it to the control unit to move the underwater vehicle to the new oil spill area, and returns to step S3.

8. The detection method according to claim 7, characterized in that: Step S3 includes the following steps: S31: The control unit controls the ultrasonic signal transceiver unit to start measurement, and simultaneously measures the thickness of the oil spill on the sea surface above the motion trajectory in real time; S32: The ultrasonic probe transmits the ultrasonic signal stimulated by the ultrasonic signal transceiver unit toward the sea surface, and receives the ultrasonic signal reflected from the oil layer and water reflection surface and the oil layer and air reflection surface. At the same time, the ultrasonic signal transceiver unit records the current time information and sends the digitized ultrasonic reflection signal and the corresponding time information to the ultrasonic signal processing and storage unit; S33: The ultrasonic signal processing and storage unit analyzes the ultrasonic reflection signal using an ultrasonic signal processing algorithm, extracts the round-trip propagation time of the ultrasonic wave between the oil layer and the water reflection surface and between the oil layer and the air reflection surface, and obtains the thickness of the oil layer based on the propagation time; records the digital signal sent by the ultrasonic signal transceiver unit, the oil spill thickness information, and the corresponding time information, and simultaneously sends the thickness and time information to the control unit; S34: At fixed intervals, the control unit sends the oil layer thickness and corresponding time information measured by the ultrasonic signal processing and storage unit, the position and corresponding time information measured by the positioning and navigation unit, and the battery remaining information to the underwater acoustic communication unit, and then sends it to the command center through the wireless communication method of the underwater acoustic communication unit.

9. The detection method according to claim 8, characterized in that: The ultrasonic signal processing algorithm in step S33 adopts a first-order correlation method, which includes the following steps: S331: using two time windows to extract the reflection signals of the oil layer and the water reflection surface and the oil layer and the air reflection surface respectively; S332: Perform a correlation operation on the two channel signals. The peak point corresponding to the correlation function is the time delay between the two reflected signals, that is, the round-trip propagation time τ; S333: According to the round-trip propagation time τ, the thickness of the oil layer is obtained, that is: THK=c×τ / 2 Where c is the propagation speed of ultrasound in the oil spill layer.

10. The detection method according to claim 7, characterized in that: In step S3, for the oil spill thickness measurement result at each measurement point, an average method of multiple measurements is adopted to eliminate abnormal measurement values.

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