An underwater positioning method and system

Abstract

The application provides an underwater positioning method and system, wherein the underwater positioning system comprises a light signal processing device, a submarine optical cable and a target to be positioned. One end of the submarine optical cable is connected to the light signal processing device, and the light signal processing device controls a light source to emit a light signal which propagates in the submarine optical cable laid in advance. A vibration source is arranged in the target to be positioned, and the vibration source generates an acoustic wave signal which acts on the submarine optical cable along the line. The underwater positioning method and system provided by the application do not need to use multiple vibration sources, but can complete the positioning process through a single vibration source. The absolute position of the target to be positioned can be obtained without the target to be positioned floating to obtain a GPS positioning signal, and the mother ship does not need to follow the action, thereby saving ship time in ocean exploration and significantly reducing cost.

Description

Technical Field

[0001] This invention belongs to the field of underwater positioning, specifically relating to an underwater positioning method and system, and particularly to an accurate, rapid, and low-cost underwater positioning method and system. Background Technology

[0002] Autonomous Underwater Vehicles (AUVs), as an emerging type of marine equipment, possess underwater mobility, stealth capabilities, and swarm operation abilities, can perform a variety of underwater tasks, including seabed exploration, underwater facility maintenance, and underwater parameter data acquisition. Precise positioning of AUVs is of paramount importance for efficient and accurate underwater operations.

[0003] Existing AUV underwater navigation and positioning technologies primarily rely on onboard sensors, utilizing a pure inertial navigation system (INS) and integrating auxiliary equipment such as Doppler velocimeters and attitude reference systems. Due to inherent limitations of inertial navigation systems, positioning errors accumulate over time, gradually eroding accuracy. Furthermore, unlike land-based systems, navigation in water is significantly affected by currents; the continuous fluctuations of ocean currents further accelerate the accumulation of errors in the inertial navigation system, sometimes exceeding a thousand times the system's nominal error.

[0004] To address this issue, researchers have proposed methods for correcting the position using external information. One approach utilizes GPS to calibrate the absolute position of the AUV. However, because electromagnetic waves cannot penetrate water, GPS-like positioning methods are only effective near the ocean surface for AUVs operating at sea. This reduces the AUV's stealth capabilities and interrupts ongoing missions. Another solution involves using acoustic positioning sensors, pre-deploying surface buoys or underwater markers to achieve absolute positioning. However, this method requires numerous vessels to place beacon references, resulting in high operational costs and significant time consumption.

[0005] Currently, the mainstream positioning method is a combined approach using external calibration and the AUV's own sensors. Patent CN111595348 A discloses a master-slave cooperative positioning method for an AUV integrated navigation system. This method involves the master AUV broadcasting its own position information, and the slave AUVs obtaining their relative distance over time based on sound speed and time delay. The master AUV then uses speed and distance measurement information to perform cooperative positioning on any slave AUV, correcting the distance between them and reducing positioning errors. In the AUV-based master-slave cooperative positioning method disclosed in patent CN111595348 A, multiple AUVs can share information during each positioning cycle, using sound speed and time delay to obtain their relative distance over time, ensuring that the positioning accuracy of each AUV reaches the same order of magnitude, thus restoring positioning capability to a certain extent. However, in most current AUV operating scenarios, only one AUV is usually needed to complete underwater operations. The method described in this patent requires an additional customized AUV for positioning, resulting in extremely high additional costs. At the same time, this cooperative positioning method cannot completely correct absolute errors. In order to control error divergence, the method still requires the main AUV to surface periodically to obtain GPS positioning information, which will interrupt the execution of underwater tasks.

[0006] Patent CN 110057365 A discloses a deep-diving AUV positioning method. This method involves an AUV equipped with an underwater communication node, inertial navigation system, and temperature, salinity, and depth (TDM) sensors. A distance model between the AUV and the mother ship is constructed by combining the coordinate system position and time information transmitted between the surface mother ship and the underwater AUV with the inertial navigation information and TDM sensor information recorded by the AUV. The positioning error is then corrected online by integrating the mother ship's own positioning information. However, its application in marine surveys is limited due to the high cost of the mother ship.

[0007] In summary, existing underwater positioning methods are costly and require surfacing for correction to maintain relative accuracy, thus necessitating improvements to existing technologies. Summary of the Invention

[0008] The purpose of this invention is to provide an underwater positioning method and system, in which a light source emits an optical signal to a submarine optical cable, a vibration source emits an acoustic signal that acts on the optical signal of the submarine optical cable, and the positioning of the target to be located is achieved by combining the submarine optical cable construction route map.

[0009] To achieve the above objectives, the present invention provides an underwater positioning method comprising the following steps:

[0010] Step 1: The optical signal processing device sends an optical signal to the submarine optical cable through a light source. The optical signal enters the receiving unit and is converted into an electrical signal to obtain a reference detection signal q.

[0011] Step 2: The target to be located emits an acoustic signal S through a vibration source located inside the target. The acoustic signal S acts on the optical signal in the submarine optical cable to obtain a detection signal t1.

[0012] Step 3: Subtract the reference detection signal q from the detection signal t1 in step 2 to obtain the acoustic wave detection signal S1 of the vibration source acting on the submarine optical cable, and select the point A1 with the maximum signal amplitude of the acoustic wave detection signal S1.

[0013] Step 4: Obtain the submarine optical cable construction route map, and locate the target to be located based on the acoustic detection signal S1, the point with the maximum signal amplitude A1, and the submarine optical cable construction route map.

[0014] Furthermore, before step 4, it is determined whether the intensity of the acoustic detection signal S1 reaches a preset threshold. If yes, proceed to step 4; otherwise, the target to be located continues to move and step 2 is repeated.

[0015] Furthermore, the light source and the receiving unit are respectively connected to the same end of the submarine optical cable. The light source sends an optical signal to the submarine optical cable, and the receiving unit receives the backscattered signal of the optical signal.

[0016] Furthermore, the optical signal processing device is an optical time-domain reflectometry device.

[0017] Furthermore, the optical time-domain reflectometry device is a φ-OTDR reflectometer; or

[0018] The optical time-domain reflectometry device is a c-OTDR reflector.

[0019] Furthermore, in step 4, the intensity of the acoustic wave detection signal S1 in step 3 is substituted into the preset relationship between the acoustic wave detection signal intensity S1 and the distance between the target to be located and the submarine optical cable to obtain the distance between the target to be located and the submarine optical cable.

[0020] Furthermore, the distance between the target to be located and the optical time domain reflector is obtained based on the time difference between the speed of light v of the optical signal in the submarine optical cable and the zero point where the signal amplitude is at its maximum at point A1.

[0021] Furthermore, the target to be located is an underwater autonomous vehicle.

[0022] Furthermore, steps 1 and 2 also include signal preprocessing, which is one or more of the following methods: moving average, wavelet denoising, curve transform denoising, compressed sensing denoising, empirical mode decomposition denoising, or neural network method.

[0023] An underwater positioning system includes a vibration source, a submarine optical cable, and an optical signal processing device, wherein the optical signal processing device includes a light source, a receiving unit, and a control unit;

[0024] The light source is used to generate light signals;

[0025] The submarine optical cable is used to transmit optical signals;

[0026] The vibration source is placed in the target to be located and is used to emit sound waves that act on the optical signal.

[0027] The receiving unit is used to receive the optical signal, convert it into an electrical signal, and then transmit it to the control unit;

[0028] The control unit is used to control the light source and the receiving unit, and also includes a calculation module, which is used to execute the underwater positioning method according to any one of claims 1-9.

[0029] Furthermore, the optical signal processing device is an optical time-domain reflectometry device.

[0030] Furthermore, the optical time-domain reflectometry device is a φ-OTDR reflectometer; or

[0031] The optical time-domain reflectometry device is a c-OTDR reflector.

[0032] Furthermore, the vibration source is an engine or a broadcast sound source.

[0033] The present invention has at least the following beneficial effects: The present invention provides an underwater positioning method and system, which does not require the use of multiple vibration sources, but can complete the positioning process with a single vibration source, does not require the target to be positioned to float to obtain GPS positioning signals, and can obtain the absolute position of the target to be positioned, and does not require the mother ship to follow the movement, thus saving ship time in ocean exploration and significantly reducing cost.

[0034] The target to be located in this invention is an underwater autonomous vehicle, which is an emerging marine equipment with underwater mobility, underwater stealth and swarm operation capabilities. It can complete a number of underwater tasks such as seabed exploration, underwater facility maintenance and underwater parameter data acquisition. Combined with the underwater positioning method of this invention, underwater operations can be completed efficiently and accurately. Attached Figure Description

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0036] Figure 1 This is a flowchart of an underwater positioning method according to an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of an underwater positioning system according to an embodiment of the present invention.

[0038] In the diagram: 1-φ-OTDR reflector, 2-submarine optical cable, 3-AUV, S1-acoustic wave detection signal, A1-maximum amplitude point. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0040] The specific implementation of the present invention will be described in detail below with reference to specific embodiments. Although the following embodiments use AUV as an example, it is obvious that the present invention can also be used as an independent position tracking and navigation method and system. Therefore, the target to be located in the embodiments is not intended to limit the present invention.

[0041] To address the shortcomings of existing technologies, namely high cost of underwater positioning and the need for surfacing for correction to maintain accuracy, this invention proposes an underwater positioning method and system. This invention uses a light source to emit an optical signal to a submarine optical cable 2. A vibration source in the target object emits a vibration that generates an acoustic signal, which acts on the optical signal in the submarine optical cable 2. The location of the target object is then determined by a calculation module and a submarine optical cable construction route map. The specific steps are as follows:

[0042] like Figure 1 The diagram illustrates the steps of an underwater positioning method according to an embodiment of the present invention, including:

[0043] Step 1: The optical signal processing device sends an optical signal to the submarine optical cable 2 through the light source. The optical signal enters the receiving unit and is converted into an electrical signal to obtain the reference detection signal q.

[0044] Step 2: The target to be located emits an acoustic signal S through a vibration source located inside the target. The acoustic signal S acts on the optical signal of the submarine optical cable 2 to obtain the detection signal t1.

[0045] Step 3: Subtract the reference detection signal q from the detection signal t1 in step 2 to obtain the acoustic wave detection signal S1 along the submarine optical cable 2 caused by the vibration source, and select the point A1 with the maximum signal amplitude of the acoustic wave detection signal S1.

[0046] Step 4: Obtain the submarine optical cable construction route map. Based on the acoustic detection signal S1, the point with the maximum signal amplitude A1, and the submarine optical cable construction route map, the location of the target to be located is obtained.

[0047] Furthermore, before step S4 above, it is determined whether the intensity of the acoustic detection signal S1 has reached a preset threshold. If yes, proceed to the next step; otherwise, the target to be located continues to move and step 2 is repeated. In practical applications, if higher positioning accuracy is required, the threshold needs to be increased to meet the requirements.

[0048] The optical signal processing device of this invention is an optical time-domain reflectometry device. By injecting an optical signal into the submarine optical cable 2 and analyzing the multiple optical signals reflected back in chronological order of detection, it helps to achieve accurate and rapid underwater positioning. In this invention, the optical time-domain reflectometry device is a φ-OTDR reflector 1.

[0049] The target to be located in this invention is an AUV3, an emerging marine device with underwater mobility, underwater stealth, and swarm operation capabilities. It can perform multiple underwater tasks such as seabed exploration, underwater facility maintenance, and underwater parameter data acquisition. Combined with the underwater positioning method of this invention, underwater operations can be completed efficiently and accurately.

[0050] The light source and the receiving unit are respectively connected to the same end of the submarine optical cable 2. The light source sends an optical signal to the submarine optical cable 2, and the receiving unit receives the backscattered signal of the optical signal.

[0051] In step 1, the φ-OTDR reflector 1 emits a light signal through a light source, which propagates through the pre-laid submarine optical cable 2. Since Rayleigh scattered light is returned from all locations along the submarine optical cable 2, a continuous Rayleigh scattered light intensity signal arranged chronologically according to the detection time can be detected in the φ-OTDR reflector 1. The signal amplitude at each time point corresponds to the Rayleigh scattered light intensity at a specific location. The φ-OTDR reflector 1 reconstructs the external information distributed along the optical cable, and then uses signal preprocessing methods to eliminate background noise from the seabed environment during the detection process to obtain the reference detection signal q. These signal preprocessing methods include, but are not limited to, moving average method, wavelet denoising method, curvelet transform denoising method, compressed sensing denoising method, empirical mode decomposition denoising method, and neural network method.

[0052] In step 2, AUV3 emits an acoustic signal S with a certain amplitude and frequency through a vibration source; it is detected by φ-OTDR technology. The external disturbance information distributed along the submarine optical cable 2 and the acoustic signal S generated by AUV3 are obtained in the φ-OTDR reflector 1. After eliminating the environmental background noise and other external disturbance information by the same signal preprocessing method as in step 1, the detection signal t1 is obtained.

[0053] In step 3, the point A1 with the maximum signal amplitude corresponds to the point on the submarine optical cable 2 that is the closest to AUV3.

[0054] In step 4, the intensity of the acoustic wave detection signal S1 from step 3 is substituted into the preset relationship between the acoustic wave detection signal intensity S1 and the distance between the target to be located and the submarine optical cable to obtain the distance between the target to be located and the submarine optical cable. The distance from the point A1 with the maximum amplitude of the vibration signal to the φ-OTDR reflector 1 can be calculated by the calculation module in the processing unit of the φ-OTDR reflector 1. The distance is calculated as follows: the time difference between point A1 and the zero point connected to the φ-OTDR reflector 1 is multiplied by the speed of light v in the submarine optical cable 2 and then divided by 2.

[0055] In addition, the φ-OTDR reflector 1 of the present invention can be replaced by a C-OTDR reflector. This replacement is only a change in the method of measuring the vibration signal of the submarine optical cable, and the measurement process remains unchanged.

[0056] See the instruction manual appendix Figure 2 This is a schematic diagram of an underwater positioning system according to an embodiment of the present invention, including a φ-OTDR reflector 1 based on Rayleigh scattering, a submarine optical cable 2, and an AUV 3. The φ-OTDR reflector 1 includes a light source, a receiving unit, and a control unit. The light source generates an optical signal, the submarine optical cable 2 transmits the optical signal, and the AUV 3 is equipped with a vibration source to emit an acoustic signal S which acts on the optical signal of the submarine optical cable 2. The control unit controls the light source and the receiving unit, and also includes a calculation module. The calculation module processes electrical signals, and inputting the electrical signals into the calculation module yields the location of the target to be located.

[0057] In this invention, when implementing AUV3 positioning, one end of the submarine optical cable 2 is connected to a φ-OTDR reflector 1 as an optical time-domain reflectometry device. The control unit of the φ-OTDR reflector 1 controls the light source to emit an optical signal, which propagates in the pre-laid submarine optical cable 2. The receiving unit receives the backscattered signal of the optical signal and converts it into an electrical signal. The submarine optical cable 2 can be an existing submarine optical cable or a cable that is automatically laid in the AUV3 mission area. The AUV3 generates an acoustic signal S through a vibration source, which acts along the submarine optical cable 2. The position of the vibration source in the AUV3 can be adjusted according to the needs of the AUV3. The vibration source can generate vibration or sound waves, including but not limited to engines with unique vibrations, broadcast sound sources, etc.

[0058] Therefore, the present invention provides an underwater positioning method and system that does not require the use of multiple vibration sources, but can complete the positioning process with a single vibration source. It does not require the target to surface to obtain GPS positioning signals, but can obtain the absolute position of the target. It also does not require a mother ship to follow the target, thus saving ship time in ocean exploration and significantly reducing costs.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An underwater positioning method, characterized in that, Includes the following steps: Step 1: The optical signal processing device sends an optical signal to the submarine optical cable through a light source. The optical signal enters the receiving unit and is converted into an electrical signal to obtain the reference detection signal q. Step 2: The target to be located emits an acoustic signal S through a vibration source located inside the target. The acoustic signal S acts on the optical signal in the submarine optical cable to obtain a detection signal t1. Step 3: Subtract the reference detection signal q from the detection signal t1 in step 2 to obtain the acoustic wave detection signal S1 of the vibration source acting on the submarine optical cable, and select the point A1 with the maximum signal amplitude of the acoustic wave detection signal S1. Step 4: Obtain the submarine optical cable construction route map, and locate the target to be located based on the acoustic detection signal S1, the point with the maximum signal amplitude A1, and the submarine optical cable construction route map; The distance between the target to be located and the optical signal processing device is obtained based on the time difference between the speed of light v of the optical signal in the submarine optical cable and the zero point where the signal amplitude is at its maximum at point A1. Substituting the intensity of the acoustic wave detection signal S1 in step 3 into the preset relationship between the intensity of the acoustic wave detection signal S1 and the distance between the target to be located and the submarine optical cable, the distance between the target to be located and the submarine optical cable is obtained.

2. The underwater positioning method according to claim 1, characterized in that, Before step 4, determine whether the intensity of the acoustic detection signal S1 has reached a preset threshold. If yes, proceed to step 4; otherwise, allow the target to be located to continue moving and repeat step 2.

3. The underwater positioning method according to claim 1, characterized in that, The light source and the receiving unit are respectively connected to the same end of the submarine optical cable. The light source sends an optical signal to the submarine optical cable, and the receiving unit receives the backscattered signal of the optical signal.

4. The underwater positioning method according to claim 1, characterized in that, The optical signal processing device is an optical time-domain reflectometry device.

5. The underwater positioning method according to claim 4, characterized in that, The optical time-domain reflectometry device is a φ-OTDR reflector; or The optical time-domain reflectometry device is a c-OTDR reflector.

6. The underwater positioning method according to any one of claims 1-5, characterized in that, The target to be located is an underwater autonomous vehicle.

7. The underwater positioning method according to claim 1, characterized in that, Step 1 and Step 2 further include signal preprocessing, which is one or more of the following methods: moving average method, wavelet denoising method, curve transform denoising method, compressed sensing denoising method, empirical mode decomposition denoising method, or neural network method.

8. An underwater positioning system, characterized in that, It includes a vibration source, a submarine optical cable, and an optical signal processing device, wherein the optical signal processing device includes a light source, a receiving unit, and a control unit; The light source is used to generate light signals; The submarine optical cable is used to transmit optical signals; The vibration source is placed in the target to be located and is used to emit sound waves that act on the optical signal. The receiving unit is used to receive the optical signal, convert it into an electrical signal, and then transmit it to the control unit; The control unit is used to control the light source and the receiving unit, and also includes a calculation module, which is used to execute the underwater positioning method according to any one of claims 1-7.

9. The underwater positioning system according to claim 8, characterized in that, The optical signal processing device is an optical time-domain reflectometry device.

10. The underwater positioning system according to claim 9, characterized in that, The optical time-domain reflectometry device is a φ-OTDR reflector; or The optical time-domain reflectometry device is a c-OTDR reflector.

11. The underwater positioning system according to claim 8, characterized in that, The vibration source is an engine or a radio sound source.

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