Underwater low-frequency remote acoustic navigation method and system

Abstract

The invention relates to the technical field of navigation, and particularly discloses an underwater low-frequency remote acoustic navigation method and system.The method comprises the steps that S1, a basic positioning unit arranged on a seabed acoustic beacon is determined according to an inertial navigation precision calibration threshold of an underwater vehicle; s2, according to the basic positioning unit, the deployment sea area and the maximum duration of inertial navigation precision of the underwater vehicle, determining the layout formation of the seabed acoustic beacons; s3, laying the seabed acoustic beacons according to the laying formation; and S4, providing full-diving long-endurance navigation positioning service for the underwater vehicle by using the laid seabed acoustic beacons. According to the invention, low-frequency remote acoustics wide-area coverage application is realized, and full-submergence long-endurance high-precision navigation positioning service is provided for an underwater vehicle.

Description

Technical Field

[0001] This invention relates to the field of navigation technology, and in particular to an underwater low-frequency long-range acoustic navigation method and system. Background Art

[0002] Underwater vehicles have been rapidly adopted in fields such as underwater topographic mapping, marine geological exploration, seawater monitoring, and marine environmental monitoring due to their significant advantages, including flexibility, high overall efficiency, suitability for hazardous environments, and low life-cycle costs. Underwater navigation and positioning technology is one of the key technologies for underwater vehicles to accomplish their missions, and it is a fundamental guarantee for the effective execution of long-range navigation, mission operations, and safe recovery.

[0003] Due to the inherent characteristics of the marine environment and water medium, commonly used surface navigation methods such as radio and optical navigation cannot be used underwater. Underwater vehicles need to constantly surface to receive satellite navigation information to maintain navigation accuracy, which affects operational efficiency. Sound waves, as the only information carrier that can stably propagate over long distances in the marine medium, provide wide-area positioning services for underwater vehicles and other carriers. However, its effective range is only a few hundred kilometers, and the construction of full-area coverage will face problems of high engineering implementation difficulty and low cost-effectiveness. Summary of the Invention

[0004] This invention aims to solve the aforementioned problems. To this end, this invention provides an underwater low-frequency long-range acoustic navigation method and system, achieving wide-area coverage application of low-frequency long-range acoustic navigation and providing high-precision navigation and positioning services for underwater vehicles throughout their entire submersible journey. This invention designs the layout interval (side length) of basic positioning units based on the inertial navigation calibration threshold of the underwater vehicle, adopting an application mode of "M longitudinal lines, N transverse lines, refueling in service areas." The layout spacing between longitudinal lines and between transverse lines is designed based on the maximum duration of inertial navigation accuracy maintenance for the underwater vehicle, avoiding the problems of high implementation difficulty and low cost-effectiveness in achieving full-ocean coverage of low-frequency long-range acoustic navigation. The low-frequency long-range acoustic navigation deployment scheme adopts a square network division method, while also considering the impact of blind zones and seabed topography on the sound propagation obstruction of low-frequency long-range acoustic navigation. Low-frequency long-range acoustic navigation applications combine inertial navigation autonomous navigation equipment to perform timely underwater calibration when the accuracy of the inertial navigation system adapted to the underwater vehicle exceeds the tolerance, providing the underwater vehicle with high-precision navigation and positioning services for long-endurance, full-submersion use.

[0005] This invention provides an underwater low-frequency long-range acoustic navigation method, the technical solution of which includes the following steps: S1: Determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle; S2: Determine the deployment pattern of seabed acoustic beacons based on the maximum duration of inertial navigation accuracy maintained by the basic positioning unit, the deployment area, and the underwater vehicle; S3: Deploy underwater acoustic beacons according to the deployment pattern; S4: Utilize deployed underwater acoustic beacons to provide underwater vehicles with full-submersion, long-endurance navigation and positioning services.

[0006] Furthermore, in step S1, the deployment interval of the seabed acoustic beacons is determined based on the inertial navigation accuracy calibration threshold.

[0007] Furthermore, in step S1, the basic positioning unit is a square, and the seabed acoustic beacons are deployed at the endpoints of the square, with the deployment interval being the side length of the square.

[0008] Furthermore, in step S2, the deployment pattern adopts the form of M longitudinal lines and N transverse lines. The basic positioning units are set on the longitudinal and transverse lines. The deployment spacing between longitudinal lines and between transverse lines is calculated based on the maximum duration of the underwater vehicle's inertial navigation accuracy. The number and deployment positions of the longitudinal and transverse lines are determined based on the deployment sea area, the basic positioning units, and the deployment spacing.

[0009] Furthermore, in step S2, the maximum duration for maintaining inertial navigation accuracy is determined based on the inertial navigation equipment configured on the underwater vehicle; the deployment spacing is calculated based on the maximum duration for maintaining inertial navigation accuracy and the speed of the underwater vehicle.

[0010] Furthermore, in step S2, the spacing between the placement units is adjusted to an integer multiple of the side length of the basic positioning unit.

[0011] Furthermore, the deployment spacing is 3000km, and the side length of the basic positioning unit is 500km.

[0012] Furthermore, in step S3, candidate deployment positions of seabed acoustic beacons are obtained from the deployment array. If the actual seabed trench opening angle at the candidate deployment position is greater than or equal to the critical trench opening angle, the seabed acoustic beacon is deployed at the candidate deployment position. If the actual seabed trench opening angle is less than the critical trench opening angle, the deployment position of the seabed acoustic beacon is moved in a direction outside the basic positioning unit.

[0013] Furthermore, in step S4, the underwater vehicle enters the basic positioning unit and uses a factor map combination method to directly correct the inertial navigation underwater, without the underwater vehicle needing to surface.

[0014] This invention also provides an underwater low-frequency long-range acoustic navigation system, the technical solution of which is as follows: including a basic positioning unit calculation module, a deployment array calculation module, and an underwater acoustic beacon. The basic positioning unit calculation module is used to determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle. The deployment array calculation module is used to determine the deployment array of seabed acoustic beacons based on the basic positioning unit, the deployment sea area, and the maximum duration of the inertial navigation accuracy of the underwater vehicle. The underwater acoustic beacons are deployed according to the array pattern to provide underwater vehicles with full-submersion, long-endurance navigation and positioning services.

[0015] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: 1. This invention adopts an array configuration of M longitudinal lines and N transverse lines, with adjacent basic positioning units sharing seabed acoustic beacons. The number and position of longitudinal and transverse lines are determined by combining the deployment area boundary and blind zone. Compared with unoptimized deployment across the entire sea area, this invention significantly reduces the number of acoustic beacons used, thereby reducing the workload and cost of equipment procurement and seabed deployment.

[0016] 2. This invention maintains the maximum duration of inertial navigation accuracy, calculates the basic range (e.g., 3108km) based on the underwater vehicle's speed, and reserves redundancy. It then combines the side length of the basic positioning unit to determine the deployment spacing (e.g., 3000km), providing support for the rational design of the M-line and N-line deployment formation.

[0017] 3. This invention determines a square basic positioning unit based on the underwater vehicle's inertial navigation accuracy calibration threshold and the parameters of the underwater acoustic ranging sensor. The seabed acoustic beacons at the four endpoints of the basic positioning unit can meet the inertial navigation calibration requirements, avoiding calibration failures caused by improper beacon placement parameters, and ensuring that the positioning results are highly matched with the underwater vehicle's inertial navigation accuracy requirements.

[0018] 4. This invention combines multiple basic positioning units to form an M-line and N-line array coverage network, providing underwater vehicles with long-duration, high-precision navigation in all sea areas under full submersion with the minimum number of beacons. It does not require external positioning methods or frequent surfacing for correction, and perfectly meets the actual operational needs of underwater vehicles for long-duration, wide-range submersion.

[0019] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a flowchart of the method provided by the present invention.

[0022] Figure 2 This is a graph showing the relationship between the deployment interval and the positioning accuracy of the underwater vehicle provided by this invention.

[0023] Figure 3 This is a schematic diagram of the divergence of the inertial navigation accuracy maintenance error of the underwater vehicle provided by the present invention.

[0024] Figure 4 This is a schematic diagram showing the deployment of underwater acoustic beacons across the entire sea area.

[0025] Figure 5 This is a schematic diagram of the underwater acoustic beacon provided by the present invention, arranged in a pattern of M longitudinal lines and N transverse lines.

[0026] Figure 6 This is a schematic diagram of inertial navigation correction provided by the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. The following embodiments are used to illustrate this invention but should not be used to limit the scope of this invention.

[0028] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0029] The following is combined Figures 1 to 6 The present invention will be further described in detail below, including an underwater low-frequency long-range acoustic navigation method and system: In this embodiment, as Figure 1 As shown, an underwater low-frequency long-range acoustic navigation method is provided, comprising the following steps: S1: Determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle.

[0030] The basic positioning unit is a square, with seabed acoustic beacons deployed at the endpoints of the square. The deployment interval of the seabed acoustic beacons, i.e., the side length of the square, is determined according to the inertial navigation accuracy calibration threshold.

[0031] Based on the parameter analysis of underwater acoustic ranging sensors, a qualitative relationship is established between their deployment intervals and the positioning accuracy of underwater vehicles. Figure 2 The inertial navigation accuracy calibration threshold is set to 500m. Figure 2 This shows that the maximum deployment interval for meeting navigation accuracy calibration thresholds is 500 km. Setting the deployment interval of seabed acoustic beacons to 500 km can meet the inertial navigation calibration requirements.

[0032] Considering the one-way propagation time delay between the seabed acoustic beacon and the underwater vehicle, at least four seabed acoustic beacons are needed to locate the underwater platform. Let the coordinates of the seabed acoustic beacons be... The underwater vehicle's position coordinates are , The speed of sound underwater. The one-way propagation delay between the m-th seabed acoustic beacon and the underwater vehicle is... Let m be the distance between the m-th underwater acoustic beacon and the underwater vehicle. Based on the geometric positional relationships, we have the following system of equations: Solving the equations yields the three-dimensional position coordinates of the underwater vehicle.

[0033] The above system of equations can be written as: When the matrix When the matrix is ​​invertible, the optimal solution can be obtained using the least squares method: ,in. Here is the coefficient matrix of the system of equations. Let be the unknown vector to be solved. Let be the constant term matrix of the system of equations. This is the matrix transpose.

[0034] After receiving feedback signals from each seabed beacon, the underwater vehicle (target) obtains the signal propagation time, and then calculates the pseudorange between the underwater vehicle and each seabed beacon. , The approximate position of an underwater vehicle can be roughly provided by autonomous navigation equipment such as inertial navigation systems, serving as the initial estimated position for the receiver. The coordinates of the initial estimated position are written as... Furthermore, the solution vector for the location includes not only the spatial vector but also the underwater acoustic ranging error; therefore, the actual initial estimate is... , This is the initial estimate of the underwater acoustic ranging error. The first position is used to estimate the phase displacement from one iteration to the next. This value will be used as the convergence criterion for the iterative algorithm, thus calculating the true position of the underwater vehicle. The difference between the true position and the estimated position is represented by a vector... express, The estimation bias of the horizontal axis. The ordinate represents the estimation bias. This represents the estimation bias of the depth coordinates. This represents the estimated deviation of the ranging error.

[0035] Therefore, low-frequency long-range acoustic navigation for underwater vehicle positioning typically requires four seabed acoustic beacons to form a basic positioning unit. Furthermore, multiple basic positioning units can be combined to achieve full-ocean coverage, providing underwater vehicles with high-precision navigation and positioning services for extended submersible journeys. In this embodiment, the basic positioning unit is a square with sides of 500 km, with seabed acoustic beacons positioned at each of the four endpoints.

[0036] S2: Determine the deployment pattern of seabed acoustic beacons based on the maximum duration of the inertial navigation accuracy of the basic positioning unit, the deployment area, and the underwater vehicle.

[0037] The deployment pattern adopts an M-line longitudinal and N-line transverse configuration. The basic positioning units are set on the longitudinal and transverse lines. The spacing between longitudinal lines and transverse lines is calculated based on the maximum duration for which the inertial navigation accuracy of the underwater vehicle is maintained. The number and placement of the longitudinal and transverse lines are determined based on the deployment area, the basic positioning units, and the spacing. The basic positioning units are connected end-to-end along the longitudinal and transverse lines, meaning adjacent basic positioning units share a seabed acoustic beacon.

[0038] S2.1: Calculate the deployment spacing. Determine the maximum duration for which inertial navigation accuracy is maintained based on the inertial navigation equipment configured on the underwater vehicle; calculate the deployment spacing based on the maximum duration for which inertial navigation accuracy is maintained and the speed of the underwater vehicle.

[0039] Underwater vehicles are typically equipped with inertial autonomous navigation, but their errors accumulate and diverge over time, such as... Figure 3 As shown in the figure, the divergence process of inertial navigation latitude and longitude position error is illustrated in the following equation.

[0040] in, For latitude error, For longitude error, The top is drifting eastward. For northward gyroscope drift, The top is drifting upwards. This refers to the eastward attitude error. This refers to the northward attitude error. For the attitude error of the sky, This is the initial latitude error. This is the Earth's rotational angular velocity. For time, Latitude.

[0041] This embodiment uses a laser gyroscope inertial navigation positioning accuracy better than 2 nautical miles / 14 days as the design threshold. This means that after activation or external correction, the inertial autonomous navigation can autonomously maintain navigation and positioning accuracy for 14 days without requiring other external positioning methods. Furthermore, the deployment spacing of the low-frequency long-range acoustic navigation system is designed with the underwater vehicle's 14-day journey as a reference. The underwater vehicle's speed is typically 5 knots; therefore, using a speed of 5 knots, the underwater vehicle's 14-day journey is 3108 km. Considering factors such as ocean current interference and equipment errors, and reserving a certain redundancy, combined with the 500 km side length of the basic positioning unit, the deployment spacing in this embodiment is set to 3000 km.

[0042] In determining the deployment spacing, the side length of the basic positioning unit can be appropriately reduced, making the deployment spacing an integer multiple of the side length of the basic positioning unit. For example, the deployment spacing can be set to 2700 km, and the side length of the basic positioning unit can be set to 450 km.

[0043] S2.2: Determine the number and location of vertical and horizontal lines.

[0044] The specific process is as follows: the 3000km ocean area between the M longitudinal line and the N horizontal line is set as the deployment blind zone; then the boundary of the deployment sea area and the side length of the basic positioning unit are input into the square network partitioning method, and the deployment blind zone between the M longitudinal line and the N horizontal line is set at the same time; the actual deployment positions of the longitudinal line and the horizontal line are calculated.

[0045] Taking the deployment across the entire Pacific Ocean as an example, the implementation process of this step is explained: like Figure 4 As shown, with a deployment spacing of 500 km for the underwater acoustic beacons, the entire Pacific Ocean coverage was achieved. Figure 4 The red dots represent underwater acoustic beacons. Hundreds of underwater acoustic beacons are needed, which will present problems of high engineering difficulty and low cost-effectiveness.

[0046] This embodiment inputs the Pacific Ocean boundary coordinates (extracted from the NOAA marine database), basic positioning units (square, 500km on each side), and blind zone range (maximum side length 3000km) into ArcGIS's Grid grid generation tool to generate a grid layout map (layout pattern). For example... Figure 5 As shown, this embodiment has a format of 2 vertical lines and 3 horizontal lines. (Comparison) Figure 4 and Figure 5 The number of underwater acoustic beacons used has been significantly reduced, greatly decreasing the workload and cost of the project.

[0047] S3: Deploy underwater acoustic beacons according to the deployment pattern.

[0048] Candidate deployment locations for each seabed acoustic beacon are obtained from the deployment array. A global / regional seabed topography database is consulted, and in conjunction with equipment such as a shipborne multibeam echo sounder, the actual trench opening angle at the candidate deployment locations is determined. The influence of seabed topography on the propagation of low-frequency long-range acoustic navigation is then considered. If the actual trench opening angle is greater than or equal to the critical trench opening angle, the seabed acoustic beacon is deployed at the candidate deployment location. If the actual trench opening angle is less than the critical trench opening angle, the deployment location of the seabed acoustic beacon is adjusted, moving it outwards from the basic positioning unit, preferably towards the blind zone, to the nearest location free from topographic obstruction, and then deploying the seabed acoustic beacon there. Figure 5 As shown, two underwater acoustic beacons have been moved to blind spots due to terrain obstruction. The green dots indicate their new deployment locations.

[0049] S4: Utilize deployed underwater acoustic beacons to provide underwater vehicles with high-precision navigation and positioning services for long-duration, full-submersion operation.

[0050] The underwater vehicle utilizes its inertial autonomous navigation system to enter the basic positioning unit when accuracy exceeds tolerance, performing inertial navigation correction ("refueling in the service area"). It directly corrects inertial navigation underwater using a factor map combination method, eliminating the need for the underwater vehicle to surface to receive satellite navigation information. Seafloor acoustic beacons provide the underwater vehicle with high-precision navigation and positioning services for long-endurance, full-submersion operation.

[0051] like Figure 6 As shown, the inertial navigation correction process based on the low-frequency long-range acoustic navigation factor graph combination algorithm is as follows: the navigation variable nodes are position, velocity, and heading, and the error variable nodes include attitude error, velocity error, position error, gyroscope random drift, and addition table random drift. The navigation variable nodes at different times are updated by the variable factor nodes of the inertial measurement unit (IMU) with the highest update frequency. The connection between error variable nodes at different times is formed by error factor nodes based on the system error propagation law. Connect, measurement factor nodes This includes low-frequency long-range acoustic navigation measurement factors derived from seabed acoustic beacons. Using nonlinear solutions and optimization methods such as Gauss-Newton, the navigation variables of the underwater vehicle's calibration platform at all times are jointly optimized to achieve high-precision navigation information output from the calibration platform.

[0052] definition The navigation variables of the time-based metrology calibration platform are The error variable of the system with built-in IMU is The navigation state variables include the position, velocity, and attitude quaternions of the calibration platform; the error variables include gyroscope random drift and dial indicator random drift; and the built-in IMU measurements are... Underwater low-frequency long-range acoustic navigation measurement is Defined from the initial moment. Up to time k (current time) The set of variable nodes is , Variable nodes are a set of navigation state variables and navigation sensor system error variables; defined from the initial time... up to the current moment Measurement information set , ,in, yes Measurement information at any given time.

[0053] This embodiment also provides an underwater low-frequency long-range acoustic navigation system, which adopts the following technical solution: including a basic positioning unit calculation module, a deployment array calculation module, and an underwater acoustic beacon. The basic positioning unit calculation module is used to determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle. The deployment array calculation module is used to determine the deployment array of seabed acoustic beacons based on the basic positioning unit, the deployment sea area, and the maximum duration of the inertial navigation accuracy of the underwater vehicle. The underwater acoustic beacons are deployed according to the array pattern to provide underwater vehicles with full-submersion, long-endurance navigation and positioning services.

[0054] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for underwater low-frequency long-range acoustic navigation, characterized in that, The following steps are involved: S1: Determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle; S2: Determine the deployment pattern of seabed acoustic beacons based on the maximum duration of inertial navigation accuracy maintained by the basic positioning unit, the deployment area, and the underwater vehicle; S3: Deploy underwater acoustic beacons according to the deployment pattern; S4: Utilize deployed underwater acoustic beacons to provide underwater vehicles with full-submersion, long-endurance navigation and positioning services.

2. The underwater low-frequency long-range acoustic navigation method as described in claim 1, characterized in that, In step S1, the deployment interval of the seabed acoustic beacons is determined according to the inertial navigation accuracy calibration threshold.

3. The underwater low-frequency long-range acoustic navigation method as described in claim 2, characterized in that, In step S1, the basic positioning unit is a square, and the underwater acoustic beacons are deployed at the endpoints of the square, with the deployment interval being the side length of the square.

4. The underwater low-frequency long-range acoustic navigation method as described in claim 1, characterized in that, In step S2, the deployment pattern adopts the form of M longitudinal lines and N transverse lines. The basic positioning units are set on the longitudinal and transverse lines. The deployment spacing between longitudinal lines and between transverse lines is calculated based on the maximum duration of the underwater vehicle's inertial navigation accuracy. The number and deployment positions of the longitudinal and transverse lines are determined based on the deployment sea area, the basic positioning units, and the deployment spacing.

5. The underwater low-frequency long-range acoustic navigation method as described in claim 4, characterized in that, In step S2, the maximum duration for maintaining inertial navigation accuracy is determined based on the inertial navigation equipment configured on the underwater vehicle; the deployment spacing is calculated based on the maximum duration for maintaining inertial navigation accuracy and the speed of the underwater vehicle.

6. The underwater low-frequency long-range acoustic navigation method as described in claim 4 or 5, characterized in that, In step S2, the layout spacing is adjusted to an integer multiple of the side length of the basic positioning unit.

7. The underwater low-frequency long-range acoustic navigation method as described in claim 6, characterized in that, The deployment spacing is 3000km, and the side length of the basic positioning unit is 500km.

8. The underwater low-frequency long-range acoustic navigation method as described in claim 1, characterized in that, In step S3, candidate deployment locations for seabed acoustic beacons are obtained from the deployment array. If the actual trench opening angle at the candidate deployment location is greater than or equal to the critical trench opening angle, then the seabed acoustic beacon is deployed at the candidate deployment location. If the actual trench opening angle is less than the critical trench opening angle, the location of the seabed acoustic beacon will be moved outside the basic positioning unit.

9. The underwater low-frequency long-range acoustic navigation method as described in claim 1, characterized in that, In step S4, the underwater vehicle enters the basic positioning unit and uses a factor graph combination method to directly correct the inertial navigation underwater, without the underwater vehicle needing to surface.

10. An underwater low-frequency long-range acoustic navigation system, characterized in that, The underwater low-frequency long-range acoustic navigation method, as described in any one of claims 1 to 9, comprises: a basic positioning unit calculation module, a deployment array calculation module, and an underwater acoustic beacon. The basic positioning unit calculation module is used to determine the basic positioning unit for the deployment of seabed acoustic beacons based on the inertial navigation accuracy calibration threshold of the underwater vehicle. The deployment array calculation module is used to determine the deployment array of seabed acoustic beacons based on the basic positioning unit, the deployment sea area, and the maximum duration of the inertial navigation accuracy of the underwater vehicle. The underwater acoustic beacons are deployed according to the array pattern to provide underwater vehicles with full-submersion, long-endurance navigation and positioning services.

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