Underwater target ultra-short baseline positioning method and system considering sound ray bending

Abstract

The present application relates to underwater target positioning technical field, especially in kind consider sound line bending's underwater target ultra-short baseline positioning method and system, first obtain arbitrary adjacent position two hydrophone received sound signal's time difference of arrival; then all independent time difference of arrival observation value is made into observation vector; next according to least square principle, the optimal estimate of direction of arrival is calculated;Again according to the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system, the initial incidence angle of the beam is calculated;Based on the initial incidence angle of the beam, the sound signal propagation time delay obtained by the ultra-short baseline system and the draft of the ultra-short baseline system, the horizontal displacement and depth of the underwater target are calculated by using the constant gradient sound line tracking method;Finally, the coordinate vector of the underwater target in the local horizontal coordinate system is calculated by using the direction of arrival and the horizontal displacement and depth of the underwater target.The present application considers the influence of sound line bending on ultra-short baseline ranging and direction finding, and improves the positioning accuracy of underwater target.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater target positioning, and in particular to an ultra-short baseline positioning method and system for underwater targets taking into account sound line bending. Background Art

[0002] Ultra-short baseline positioning accuracy is a critical factor affecting the mission execution capability of underwater equipment. Existing research on how to improve ultra-short baseline positioning accuracy primarily focuses on improving the quality of USBL raw observations through signal processing, such as using methods such as generalized cross-correlation, adaptive minimum mean square error, recursive least squares, and Fourier transforms to estimate time delay, time delay difference, or phase difference. Improving the quality of raw observations will inevitably improve USBL positioning accuracy. However, the bending of sound lines caused by the spatiotemporal variations in underwater sound speed results in USBL measurements using direction of arrival (DOA) rather than the line of sight (LOS) of the underwater target, a key contributor to USBL positioning errors. There are two main existing ultra-short baseline positioning methods. The conventional ultra-short baseline positioning method directly uses azimuth and distance to calculate the position of underwater targets, regards sound waves as propagating in a straight line, and does not consider the impact of sound line bending on ultra-short baseline positioning; the deep-sea ultra-short baseline iterative positioning method based on constant sound velocity sound line tracking uses the depth information of underwater targets to accurately calculate the horizontal distance of the target under the condition that the initial incident angle of the beam is unknown. This method does not use the azimuth information of ultra-short baseline observations and requires the assistance of depth sensors, which increases the complexity and signal interaction load of the ultra-short baseline positioning system. Summary of the Invention

[0003] The present invention aims to solve the problem that sound waves are currently regarded as propagating in a straight line without considering the influence of sound line bending on ultra-short baseline positioning. A method and system for ultra-short baseline positioning of underwater targets taking into account sound line bending is proposed. This method takes into account the influence of sound line bending on ultra-short baseline ranging and direction finding, thereby improving the positioning accuracy of underwater targets.

[0004] In order to achieve the above purpose, the technical solutions adopted are:

[0005] A method for ultra-short baseline positioning of underwater targets taking into account sound line bending comprises the following steps:

[0006] Firstly, the far-field model is used to approximate the acoustic wave sent by the underwater target as a plane wave, and the arrival time difference of the acoustic signal received by two hydrophones at any adjacent position is obtained.

[0007] Then all independent arrival time difference observations are combined into an observation vector;

[0008] Then, based on the least squares principle, the optimal estimate of the direction of arrival is calculated;

[0009] Then, the initial incident angle of the beam is calculated based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system;

[0010] Based on the initial incident angle of the beam, the propagation delay of the acoustic signal acquired by the ultra-short baseline system, and the draft of the ultra-short baseline system, the horizontal displacement and depth of the underwater target are calculated using the constant gradient acoustic ray tracking method.

[0011] Finally, the coordinate vector of the underwater target in the local horizontal coordinate system is calculated using the wave arrival direction and the horizontal displacement and depth of the underwater target.

[0012] According to the ultra-short baseline positioning method for underwater targets taking into account the curvature of the sound line, the far-field model is further used to approximate the sound waves sent by the underwater target as plane waves, and the arrival time difference of the sound signals received by two hydrophones at any adjacent positions is obtained. The calculation formula is as follows:

[0013]

[0014] Where, δ i,j is the arrival time difference of the acoustic signals received by hydrophones i and j, p represents the position vector of the hydrophone in the USBL carrier coordinate system, and the subscript represents the hydrophone number; the unit vector d represents the direction of arrival of the acoustic signal when it arrives at the ultra-short baseline receiving array, and c represents the sound speed at the ultra-short baseline transceiver.

[0015] According to the underwater target ultra-short baseline positioning method taking into account the bending of the sound line of the present invention, further, all independent arrival time difference observation values ​​are combined into an observation vector as follows:

[0016] Δ=[δ 1,2 δ 2,3 …δ N-1,N ] T .

[0017] According to the underwater target ultra-short baseline positioning method taking into account the sound line bending of the present invention, further, according to the least squares principle, the optimal estimate of the direction of arrival is calculated. for:

[0018]

[0019] Where A is the coefficient matrix, which is expressed as follows:

[0020]

[0021] According to the underwater target ultra-short baseline positioning method taking into account the bending of the sound line of the present invention, the initial beam incidence angle is further calculated based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system. The calculation formula is as follows:

[0022]

[0023] wherein n z =

[001] T is a unit normal vector of the horizontal plane in the local horizontal coordinate system, represents a rotation matrix from the ultra-short baseline carrier coordinate system to the local horizontal coordinate system, which is obtained by the attitude sensor of the ultra-short baseline system.

[0024] According to the underwater target ultra-short baseline positioning method considering sound ray bending of the application, further, the horizontal displacement and the depth of the underwater target are used to calculate the coordinate vector of the underwater target in the local horizontal coordinate system, and the calculation formula is as follows:

[0025]

[0026] wherein, is a coordinate vector of the underwater target in the local horizontal coordinate system, and s represents a two-dimensional column vector composed of the first two elements of is a two-dimensional column vector composed of the first two elements of e and z e are the horizontal displacement and the depth calculated by the sound ray tracing method.

[0027] Further, the application also provides an underwater target ultra-short baseline positioning system considering sound ray bending, comprising:

[0028] a time difference of arrival calculation module, which is used to approximate the underwater target sending sound waves as plane waves by using a far field model, and obtain the time difference of arrival of sound signals received by two hydrophones at any adjacent positions;

[0029] an observation vector forming module, which is used to form an observation vector by using all independent time difference of arrival observations;

[0030] a direction of arrival optimal estimate calculation module, which is used to calculate the optimal estimate of the direction of arrival according to the least square principle;

[0031] a beam initial incidence angle calculation module, which is used to calculate the beam initial incidence angle according to the direction of arrival and the rotation matrix obtained by the attitude sensor of the ultra-short baseline system;

[0032] a horizontal displacement and depth obtaining module, which is used to calculate the horizontal displacement and the depth of the underwater target by using the constant gradient sound ray tracing method based on the beam initial incidence angle, the sound signal propagation time delay obtained by the ultra-short baseline system and the draft depth of the ultra-short baseline system;

[0033] an underwater target position calculation module, which is used to calculate the coordinate vector of the underwater target in the local horizontal coordinate system by using the direction of arrival and the horizontal displacement and the depth of the underwater target.

[0034] The beneficial effects achieved by adopting the above technical solution are:

[0035] Compared to conventional underwater target ultra-short baseline positioning methods, the present invention takes into account the impact of sound line bending on ultra-short baseline ranging and direction finding, resulting in more accurate positioning. Compared to deep-sea ultra-short baseline iterative positioning methods based on constant-speed sound line tracking, this method does not require additional depth sensors, ensuring the portability and flexibility of the system. The present invention utilizes the inherent transmitting transducer, receiving array, and IMU of the ultra-short baseline system to achieve high-precision positioning without the influence of sound line bending, thereby improving the accuracy of ultra-short baseline positioning without increasing the complexity of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings of the embodiments of the present invention. The drawings are only used to illustrate some embodiments of the present invention, but not to limit all embodiments of the present invention thereto.

[0037] Figure 1 1 is a flow chart of an underwater target ultra-short baseline positioning method taking into account sound line bending according to an embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the initial incident angle of the beam according to an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The following will be combined with the accompanying drawings of specific embodiments of the present invention to clearly and completely describe the exemplary embodiments of the present invention. Unless otherwise defined, technical or scientific terms used in the present invention should be given the common meanings understood by people with ordinary skills in the relevant field.

[0040] The distance observation value of the ultra-short baseline is affected by the bending of the sound line, and the actual representation is not the spatial distance; the azimuth observation value of the ultra-short baseline (USBL) is also affected by the bending of the sound line, and actually represents the direction of arrival rather than the direction of line of sight, which is a major factor limiting its positioning accuracy. To address the problem of inconsistency between the direction of arrival and the direction of line of sight, existing methods generally regard the target depth as error-free or extremely accurate. However, this premise does not conform to the actual situation that the measurement error of the pressure depth gauge increases linearly with increasing depth, resulting in unsatisfactory actual results of existing methods. Moreover, depth information requires the underwater target to be equipped with a depth sensor and transmit the depth value to the ultra-short baseline transceiver, which increases the complexity of the system.

[0041] In order to theoretically eliminate the influence of sound ray bending on the ultra-short baseline positioning, the underwater target ultra-short baseline positioning method considering sound ray bending disclosed by the embodiment converts the azimuth observation value in the ultra-short baseline carrier coordinate system (b system) to the local horizontal coordinate system (l system) by using the attitude information to calculate the beam initial incidence angle, and then combines the round trip delay (RTD) observation value and calculates the underwater target position according to the constant gradient sound ray tracking method. As shown in Figure 1 , the method specifically includes the following steps:

[0042] Step S101, the underwater target transmitted sound wave is approximated as a plane wave by using a far-field model, and a time difference of arrival calculation formula of sound signals received by any adjacent position two hydrophones is obtained as follows:

[0043]

[0044] In the formula, δ i,j is the time difference of arrival (TDOA) of sound signals received by hydrophones i and j, also known as time delay difference (TDD); p represents the position vector of the hydrophone in the USBL carrier coordinate system, and the subscript represents the hydrophone number; the unit vector d represents the direction of arrival (direction vector) of the sound signal when it reaches the ultra-short baseline receiving array; and c represents the sound speed at the ultra-short baseline transceiver.

[0045] Step S102, the observation vector is composed of all independent TDOA / TDD observation values as follows:

[0046] Δ=[δ 1,2 δ 2,3 … δ N-1,N ] T .

[0047] Step S103, according to the least square principle, the optimal estimate of the direction of arrival (direction vector) is calculated as follows:

[0048]

[0049] In the formula, A is a coefficient matrix composed of position vectors, and its expression is as follows:

[0050]

[0051] Step S104, as shown in Figure 2 , the beam initial incidence angle is calculated according to the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system, and the calculation formula is as follows:

[0052] ​

[0053] Where n z =[0 0 1] T is the unit normal vector of the horizontal plane in the local horizontal coordinate system, Represents the rotation matrix from the ultra-short baseline carrier coordinate system to the local horizontal coordinate system, obtained by the attitude sensor of the ultra-short baseline system.

[0054] Step S105 : Calculate the horizontal displacement and depth of the underwater target using a constant gradient ray tracking method based on the initial incident angle of the beam, the acoustic signal propagation delay acquired by the ultra-short baseline system, and the draft of the ultra-short baseline system.

[0055] Step S106: Calculate the coordinate vector of the underwater target in the local horizontal coordinate system using the direction of arrival (direction vector) and the horizontal displacement and depth of the underwater target. The calculation formula is as follows:

[0056]

[0057] Where, is the coordinate vector of the underwater target in the local horizontal coordinate system, s represents the coordinate vector of the underwater target in the local horizontal coordinate system. The first two elements of the two-dimensional column vector, Δp e and z e are the horizontal displacement and depth calculated by the ray tracing method.

[0058] Corresponding to the above method, this embodiment further proposes an underwater target ultra-short baseline positioning system that takes into account sound ray bending, including:

[0059] The arrival time difference calculation module is used to approximate the sound waves sent by the underwater target as plane waves using the far-field model, and obtain the arrival time difference of the sound signals received by two hydrophones at any adjacent positions.

[0060] The observation vector composition module is used to compose an observation vector from all independent arrival time difference observation values.

[0061] The optimal estimation module of the direction of arrival is used to calculate the optimal estimation of the direction of arrival based on the least squares principle.

[0062] The beam initial incidence angle calculation module is used to calculate the beam initial incidence angle based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system.

[0063] The horizontal displacement and depth acquisition module is used to calculate the horizontal displacement and depth of underwater targets using the constant gradient ray tracking method based on the initial incident angle of the beam, the acoustic signal propagation delay obtained by the ultra-short baseline system, and the draft depth of the ultra-short baseline system.

[0064] The underwater target position calculation module is configured to calculate a coordinate vector of the underwater target in a local horizontal coordinate system by using the direction of arrival and horizontal displacement and depth of the underwater target.

[0065] The application considers the influence of sound ray bending on ultra-short baseline ranging and direction finding, and makes the underwater target positioning more accurate.

[0066] Unless specifically stated otherwise, the relative steps, numerical expressions, and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present application.

[0067] The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other. For the system disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0068] The units and method steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been described in the above description in general terms. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation does not exceed the scope of the present application.

[0069] Those skilled in the art can understand that all or part of the steps in the above method can be instructed by a program to complete the relevant hardware, and the program can be stored in a computer readable storage medium, such as a read-only memory, a magnetic disk or an optical disk. Alternatively, all or part of the steps of the above embodiments can also be implemented using one or more integrated circuits, and accordingly, each module / unit in the above embodiments can be implemented in the form of hardware or in the form of a software function module. The present application is not limited to any specific form of combination of hardware and software.

[0070] Finally, it should be noted that the above-described embodiments are merely specific embodiments of the present application, which are used to illustrate the technical solutions of the present application, but not to limit the same. The protection scope of the present application is not limited thereto. Although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that any person skilled in the art can still modify or easily think of changes to the technical solutions recorded in the foregoing embodiments, or make equivalent replacements to some of the technical features, within the technical scope disclosed by the present application. The modifications, changes or replacements do not cause the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for ultra-short baseline positioning of underwater targets taking into account sound line bending, characterized in that: The following steps are involved: Firstly, the far-field model is used to approximate the acoustic wave sent by the underwater target as a plane wave, and the arrival time difference of the acoustic signal received by two hydrophones at any adjacent position is obtained. Then all independent arrival time difference observations are combined into an observation vector; Then, based on the least squares principle, the optimal estimate of the direction of arrival is calculated; Then, the initial incident angle of the beam is calculated based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system; Based on the initial incident angle of the beam, the propagation delay of the acoustic signal acquired by the ultra-short baseline system, and the draft of the ultra-short baseline system, the horizontal displacement and depth of the underwater target are calculated using the constant gradient acoustic ray tracking method. Finally, the coordinate vector of the underwater target in the local horizontal coordinate system is calculated using the wave arrival direction and the horizontal displacement and depth of the underwater target.

2. The underwater target ultra-short baseline positioning method taking into account sound line bending according to claim 1 is characterized in that: The far-field model is used to approximate the sound waves sent by underwater targets as plane waves, and the arrival time difference of the sound signals received by two hydrophones at any adjacent positions is obtained. The calculation formula is as follows: Where, δ i,j is the arrival time difference of the acoustic signal received by hydrophones i and j, p represents the position vector of the hydrophone in the USBL carrier coordinate system, and the subscript represents the hydrophone number; the unit vector d represents the direction of arrival of the acoustic signal when it arrives at the ultra-short baseline receiving array, c represents the speed of sound at the ultra-short baseline transceiver, and ε i represents the error term.

3. The underwater target ultra-short baseline positioning method taking into account sound line bending according to claim 2 is characterized in that: All independent arrival time difference observations are combined into an observation vector: Δ=[δ 1,2 d 2,3 Lδ N-1,N ] T 。 4. The underwater target ultra-short baseline positioning method taking into account sound line bending according to claim 3 is characterized in that: Calculate the optimal estimate of the direction of arrival based on the least squares principle for: Where A is the coefficient matrix, which is expressed as follows:

5. The underwater target ultra-short baseline positioning method taking into account sound line bending according to claim 4 is characterized in that: The initial beam incidence angle is calculated based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system. The calculation formula is as follows: Where n z =[001] T is the unit normal vector of the horizontal plane in the local horizontal coordinate system, Represents the rotation matrix from the ultra-short baseline carrier coordinate system to the local horizontal coordinate system, obtained by the attitude sensor of the ultra-short baseline system.

6. The underwater target ultra-short baseline positioning method taking into account sound line bending according to claim 5 is characterized in that: The coordinate vector of the underwater target in the local horizontal coordinate system is calculated using the wave direction and the horizontal displacement and depth of the underwater target. The calculation formula is as follows: Where, is the coordinate vector of the underwater target in the local horizontal coordinate system, s represents the coordinate vector of the underwater target in the local horizontal coordinate system. The first two elements of the two-dimensional column vector, Δp e and z e are the horizontal displacement and depth calculated by the ray tracing method.

7. An underwater target ultra-short baseline positioning system taking into account sound line bending, characterized in that: include: The arrival time difference calculation module is used to approximate the sound waves sent by underwater targets as plane waves using a far-field model, and obtain the arrival time difference of the sound signals received by two hydrophones at any adjacent position; An observation vector construction module is used to combine all independent arrival time difference observations into an observation vector; The optimal estimation calculation module of the direction of arrival is used to calculate the optimal estimation of the direction of arrival based on the least squares principle; The beam initial incidence angle calculation module is used to calculate the beam initial incidence angle based on the direction of arrival and the rotation matrix obtained by the attitude sensor on the ultra-short baseline system; The horizontal displacement and depth acquisition module is used to calculate the horizontal displacement and depth of underwater targets using a constant gradient ray tracking method based on the initial incident angle of the beam, the propagation delay of the acoustic signal acquired by the ultra-short baseline system, and the draft depth of the ultra-short baseline system; The underwater target position calculation module is used to calculate the coordinate vector of the underwater target in the local horizontal coordinate system using the wave arrival direction and the horizontal displacement and depth of the underwater target.

8. A computer device comprising a memory, a processor, and a computer program stored in the memory, wherein: The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 6 are implemented.

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