A broadcast underwater navigation and positioning system and method

Abstract

The present invention discloses a broadcast underwater navigation and positioning system and method, the system includes a base station network composed of multiple underwater base stations distributed on the seabed and a user terminal to be positioned underwater, the underwater base station includes a bottom-mounted sonar and an anchored sonar, the bottom-mounted sonar and the anchored sonar are connected by a cable, and use hydroacoustic signals for ranging and communication, the anchored sonar is integrated with an inertial measurement unit 1, and the user terminal is configured with a passive sonar, and the passive sonar unidirectionally receives the hydroacoustic signal emitted by the anchored sonar for ranging and communication. The underwater navigation and positioning system and method disclosed in the present invention can expand the service range of base stations, increase the capacity of user terminals, and improve the accuracy of regional sound speed products.

Description

Technical Field

[0001] The invention belongs to the field of underwater navigation and positioning, and in particular relates to a broadcast underwater navigation and positioning system and method. Background Art

[0002] Due to the attenuation and obstruction of seawater, satellite navigation positioning (GNSS) signals cannot be used for underwater and seabed navigation and positioning. The main underwater navigation and positioning technologies include acoustics, inertial, matching (terrain, gravity, magnetism, etc.). Due to the defects of the technology itself, inertial navigation has drift and needs regular calibration. Matching navigation requires background fields and characteristic environments, large matching errors, and low availability. At present, acoustics is the main technical method for underwater navigation and positioning. However, there are problems in underwater acoustic navigation and positioning, such as small base station service range, short operating distance, small terminal user capacity, and low positioning accuracy, as follows.

[0003] (1) Small service range of base stations: In the currently established local underwater acoustic positioning system, due to the negative curvature of the sound line (close to the seabed), the distance between the seabed base stations is generally designed to be only 1-2 km, and the base station height is generally 2-3 m. In addition, in order to ensure line of sight of the sound line and to measure the distance and communicate between the base stations, the base station height must be increased by about 3 m for every 1 km increase in the base station spacing, which greatly increases the difficulty of base station construction and maintenance costs. Under this configuration, if the underwater positioning system is to serve users in a large range (for example, tens or hundreds of kilometers), it is necessary to build a large number of base stations and perform position calibration operations, which is extremely costly and inefficient.

[0004] (2) Small terminal user capacity. Currently, underwater positioning mainly adopts the response positioning mode, which requires distinguishing the inquiry signals sent by different user terminals. The number of users served at the same time is extremely limited, and the active mode easily exposes the user's location. It is not suitable for the synchronous work and concealment requirements of a large number of underwater operation targets.

[0005] (3) Low positioning accuracy. At present, the error in measuring the speed of sound in seawater is generally not less than 5 cm / s. The sound speed measurement error and its temporal and spatial variations and low observation geometry intensity of underwater acoustic navigation positioning lead to problems such as poor three-dimensional positioning accuracy of the terminal and low operating efficiency.

[0006] It can be seen that the main factors affecting the underwater positioning performance of the terminal are the maintenance of the time and space reference of the underwater base station, the observation geometry structure of the terminal, and the sound speed error and its time and space variation. In response to the above three problems, three key technologies need to be focused on, namely the expansion of the service area of ​​the underwater base station, the precise time synchronization between base stations and between base stations and user terminals in broadcast positioning, and the fine processing and correction of the sound speed error.

[0007] With the increase of long-distance, high-precision deep-sea applications (such as seabed resource exploration, near-bottom multi-beam measurement, AUV networking, etc.), it is necessary to study wide-coverage hydroacoustic measurement technology to increase end-user capacity while ensuring high accuracy. Summary of the invention

[0008] In order to solve the above technical problems, the present invention provides a broadcast underwater navigation and positioning system and method, so as to achieve the purpose of expanding the service range of base stations, increasing user terminal capacity, and improving the accuracy of regional sound speed structure.

[0009] To achieve the above object, the technical solution of the present invention is as follows:

[0010] A broadcast underwater navigation and positioning system comprises a base station network composed of a plurality of underwater base stations distributed on the seabed and a user terminal to be positioned underwater, wherein the underwater base station comprises a bottom-mounted sonar and an anchored sonar, the bottom-mounted sonar and the anchored sonar are connected by a cable and use hydroacoustic signals for ranging and communication, the anchored sonar is integrated with an inertial measurement unit 1, and the user terminal is configured with a passive sonar, which unidirectionally receives the hydroacoustic signal emitted by the anchored sonar for ranging and communication.

[0011] In the above solution, the anchored sonar is also integrated with a temperature, salinity and depth measuring instrument, a pressure gauge, a current meter and a pressure gauge, and the user terminal is also configured with an inertial measurement unit 2.

[0012] A broadcast underwater navigation and positioning method, using the above-mentioned broadcast underwater navigation and positioning system, comprises the following steps:

[0013] Step 1: Use GNSS-acoustic ranging positioning technology to obtain the position coordinates of each bottom-mounted sonar;

[0014] Step 2: The anchored sonar and the bottom-mounted sonar perform response measurement through hydroacoustic signals, and the position coordinates of the anchored sonar are calculated according to the time delay of the hydroacoustic signal measured by the anchored sonar and the observation value of the inertial measurement unit 1;

[0015] Step three: the anchored sonar generates and broadcasts the hydroacoustic ranging signal and sound speed correction data at a predetermined time interval. After the passive sonar of the user terminal receives the hydroacoustic ranging signal and sound speed correction data broadcast by the anchored sonar, it decodes and obtains the hydroacoustic time delay and sound speed correction data from the time the hydroacoustic ranging signal is transmitted to the time the hydroacoustic ranging signal is received, and determines its own position based on the hydroacoustic time delay and sound speed correction data. During the positioning process, regular time synchronization is performed between the anchored sonars of each underwater base station, as well as between the user terminal and the base station network.

[0016] In a further technical solution, in step 2, data measured by a temperature, salinity and depth measuring instrument, a pressure gauge and a current meter integrated on the moored sonar are used to assist in calculating the position coordinates of the moored sonar.

[0017] In the above scheme, the method for generating the sound speed correction data includes the following steps:

[0018] (1) Calculate the sound speed using multi-source data, decompose the sound speed into spatial function and time function, and construct the sound speed background field;

[0019] (2) Taking the constructed sound velocity background field as a priori value and the propagation delay data of the underwater acoustic ranging signal observed in real time between the anchored sonars of each underwater base station as input, the propagation delay of the underwater acoustic ranging signal caused by the sound velocity error including the horizontal gradient is obtained;

[0020] (3) The propagation delay of the underwater acoustic ranging signal caused by the sound velocity error is used to construct the sound velocity error tomographic equation group, and the regional sound velocity error inversion is performed by adding constraints;

[0021] (4) Generate sound speed correction data using the regional sound speed error obtained in the previous step and the sound speed reference customized by the base station system.

[0022] In the above scheme, the time synchronization between the moored sonars of each underwater base station is achieved through two response measurements between the two moored sonars, and the flow velocity and flow direction measured by the current meter are used for correction, so as to achieve the time synchronization between the two moored sonars. The specific method is as follows:

[0023] Anchored sonar A transmits a pulse signal, and anchored sonar B receives the pulse signal and processes it to obtain the time delay t B1 ; Then, the mooring sonar B responds with a pulse signal after the agreed delay Δd, and the mooring sonar A receives the pulse signal; Then, the mooring sonar A responds with a pulse signal again after the same agreed delay Δd, and the mooring sonar B receives the pulse signal and processes it to obtain the time delay t between the mooring sonar B sending and receiving the two pulse signals B2 ;

[0024] Assume that the current correction is Δc. If there is no current observation, Δc = 0. Then the anchored sonar B can measure the t B1 and t B2 The synchronization time deviation ΔT between the anchored sonar B and the anchored sonar A is calculated as: ΔT = 0.5*(t B2 -Δd)+Δc-t B1 ; The anchored sonar B adjusts its own clock according to the synchronization time deviation ΔT to achieve time synchronization with the anchored sonar A;

[0025] The same method can be used to obtain the synchronization time deviation between other anchored sonars and anchored sonar A, and the same method can be used to obtain the synchronization time deviation between any two adjacent anchored sonars, and the synchronization deviation can be corrected to achieve precise time synchronization between all anchored sonars.

[0026] In the above scheme, the time synchronization method between the user terminal and the base station network is as follows:

[0027] The clock error model of the user terminal is described as a quadratic polynomial model:

[0028] Δt=a 0 +a 1 (tt oc )+a 2 (tt oc ) 2 ;

[0029] Where Δt is the clock difference between the user terminal and the base station network, t oc represents the starting reference time selected by the clock error model, a 0 、a 1 、a 2 are the clock deviation, clock speed and frequency drift parameters of the user terminal clock respectively, and t is the time when the user terminal receives the sound signal;

[0030] When the user terminal receives the base station network underwater acoustic ranging signal to determine its own position, the clock error Δt obtained by parameter estimation is substituted into the above formula to obtain a 0 、a 1 、a 2 When the user terminal does not receive the underwater acoustic ranging signal from the base station network, the clock error Δt is predicted by the quadratic polynomial model to complete the time synchronization between the user terminal and the base station network.

[0031] In the above scheme, the method for constructing the sound velocity background field in step (1) is as follows: using the existing regional ocean analysis data and the temperature, salinity and depth of the numerical forecast model as background field constraints, adding the measured data of the temperature, salinity and depth measuring instrument integrated on the anchored sonar, and fusing the multi-source data to obtain the sound velocity; analyzing the optimal boundary depth of the sound velocity profile based on the spatial distribution characteristics of the sound velocity and the service area of ​​the base station network; performing layered empirical orthogonal function decomposition based on the depth, and decomposing the sound velocity into a spatial function and a time function; then using the fitted time function and space function to represent the sound velocity at any time and position, to realize the construction of a regional three-dimensional time-varying sound velocity background field.

[0032] In the above scheme, in step (2), the propagation delay of the underwater acoustic ranging signal caused by the sound speed error is expressed as:

[0033]

[0034]

[0035] M Δ (θ)=M(θ)tanθ=M(ε)cotε

[0036] Where δT is the propagation delay of the underwater acoustic ranging signal caused by the sound speed error, δT NTD , M(θ) are the total nadir delay and its projection function, G N , G E are the horizontal gradient terms in the north and east directions, M Δ (θ) is the projection function of the gradient term, θ and ε are the initial incident angle and initial grazing angle of the sound ray, respectively. is the azimuth.

[0037] In the above scheme, the formula for inversion of regional sound velocity error in step (3) is as follows:

[0038] δs=1 / (v+δv)-1 / v

[0039]

[0040] In the formula, δs is the sound speed slowness error, v is the initial sound speed, δv is the sound speed error, δT j is the propagation delay of the underwater acoustic ranging signal due to the sound velocity error of the jth acoustic signal, (x, z, t) are the plane position, depth and time of the grid respectively, dl is the integral path of the acoustic signal, Γ is the total path, i is the sub-grid number that the acoustic signal passes through, i = 1, 2, 3, ..., n.

[0041] Through the above technical solution, the broadcast underwater navigation and positioning system and method provided by the present invention have the following beneficial effects:

[0042] (1) The high-precision underwater broadcast positioning base station device of the present invention integrates bottom-mounted sonar and anchored sonar and multi-source sensors. The underwater base station adopts a combination of bottom-mounted sonar and anchored sonar. The two sonars measure the distance between each other, thereby realizing real-time online calibration of the precise position of the anchored sonar, so that the anchored sonar can be more than 100 meters away from the seabed, greatly expanding the service range of the base station, which is original.

[0043] (2) The present invention reduces the number of base stations that need to be deployed on the seabed within a certain service area, thereby reducing the time and cost required for base stations to perform position calibration using GNSS-acoustic ranging positioning technology, thereby reducing risks.

[0044] (3) The broadcast underwater positioning mode is adopted, so that the user terminal capacity is theoretically unlimited, and the user terminal positioning results can be quickly updated with low latency (e.g., update in seconds);

[0045] (4) The present invention utilizes the constructed multi-source sound velocity background field and proposes a sound velocity error tomography inversion method based on a non-uniform grid model based on the propagation delay error estimation results and slowness model of the underwater acoustic ranging signal with an additional sound velocity horizontal gradient, and generates sound velocity correction data, which can improve the accuracy of the regional sound velocity structure.

[0046] (5) The present invention can achieve real-time online position calibration accuracy of underwater base station anchored sonar to 0.1m, terminal positioning accuracy to 0.5m, regional prior sound velocity field model based on multi-source temperature, salinity and depth data to 0.5m / s, and broadcast regional sound velocity error correction product accuracy based on non-uniform grid model to 0.1m / s.

[0047] (6) The present invention can achieve the expansion of the service range and distance of underwater base stations, the precise time synchronization of broadcast positioning, and the fine processing and correction of the three-dimensional time-varying error of the speed of sound. It can effectively solve the problems of high cost, low efficiency and poor accuracy of underwater navigation and positioning, break through the technical bottlenecks that restrict the accuracy, continuity and availability of underwater navigation and positioning, and can achieve large-scale, long-distance, broadcast and high-precision underwater navigation and positioning. It can significantly improve the performance of the underwater navigation and positioning system and has important engineering and technical significance and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below.

[0049] Figure 1 A schematic diagram of a broadcast underwater navigation and positioning system disclosed in an embodiment of the present invention;

[0050] Figure 2 The present invention discloses a flowchart of online inversion of sound velocity error and generation and broadcasting of sound velocity correction data.

[0051] In the figure, 1. Underwater base station; 2. User terminal; 3. Bottom-mounted sonar; 4. Anchored sonar; 5. Cable; 6. Hydroacoustic signal; 7. Inertial measurement unit 1; 8. Pressure gauge; 9. Temperature, salinity and depth measurement instrument; 10. Current meter; 11. Passive sonar; 12. Inertial measurement unit 2. DETAILED DESCRIPTION

[0052] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0053] The main factors affecting the service range and operating distance of underwater base stations are the height of the base station sonar from the seabed and the performance of the underwater acoustic signal.

[0054] The present invention provides a broadcast underwater navigation and positioning system. Figure 1 As shown, it includes a base station network composed of multiple underwater base stations 1 distributed on the seabed and a user terminal 2 to be located underwater. The underwater base station 1 includes a bottom-mounted sonar 3 and an anchored sonar 4, and the bottom-mounted sonar 3 and the anchored sonar 4 are connected by a cable 5.

[0055] The underwater base station 1 of the present invention adopts the method of integrating the bottom-mounted sonar 3 and the anchored sonar 4, and the two sonars can measure distance and communicate with each other. Among them, the anchored sonar 4 integrates an inertial measurement unit 7 (IMU), which can be more than 100m away from the seabed, thereby greatly expanding the service area. The anchored sonar 4 can also be equipped with an integrated pressure gauge 8 for calculating the depth; the anchored sonar 4 can also be equipped with an integrated temperature, salt and depth measurement instrument 9 (CTD) for measuring temperature, salt and depth, and for constructing a sound velocity field; the anchored sonar 4 can also be equipped with an integrated single-point current meter 10 for measuring the flow velocity and direction of seawater and estimating the attitude of the anchored sonar 4. By using the hydroacoustic measurement between the bottom-mounted sonar 3 and the anchored sonar 4, the IMU observation value of the anchored sonar 4 is integrated to realize the real-time high-precision position self-calibration of the position of the anchored sonar 4. The real-time high-precision position self-calibration of the anchored sonar 4 can also integrate the measurement values ​​of sensors such as the pressure gauge 8, the temperature, salt and depth measurement instrument 9, and the current meter 10.

[0056] The user terminal 2 of the present invention is equipped with a passive sonar 11, which performs ranging and communication of the hydroacoustic signal 6 with the anchor sonar 4 of the underwater base station 1 to locate the user terminal 2. The user terminal 2 can also be equipped with an integrated inertial measurement unit 2 12 (IMU) to perform hydroacoustic and inertial combined navigation positioning of the user terminal 2.

[0057] The present invention can further improve the real-time dynamic position calibration accuracy of anchored sonar by measuring the self-test array delay between different underwater base stations 1. The broadcast underwater base station 1 of the present invention can integrate medium and low frequency sonars and can switch between broadcast synchronization and inquiry and response positioning modes.

[0058] The present invention provides a broadcast underwater navigation and positioning method, which adopts the above-mentioned broadcast underwater navigation and positioning system and comprises the following steps:

[0059] Step 1: Use GNSS-acoustic ranging positioning technology to obtain the position coordinates of each bottom-mounted sonar 3; GNSS-acoustic ranging positioning can be performed according to the deployment position of the bottom-mounted sonar 3.

[0060] Step 2: The anchored sonar 4 and the bottom-mounted sonar 3 perform response measurement through hydroacoustic signals, and calculate the position coordinates of the anchored sonar 4 according to the time delay of the hydroacoustic signal measured by the anchored sonar 4 and the observation value of the inertial measurement unit 7;

[0061] Step 3: The anchored sonar 4 generates and broadcasts the hydroacoustic ranging signal and the sound velocity correction data at a predetermined time interval, such as Figure 2As shown, after the passive sonar 11 of the user terminal 2 receives the hydroacoustic ranging signal and sound velocity correction data broadcast by the anchored sonar 4, it decodes and obtains the hydroacoustic time delay and sound velocity correction data from the time the hydroacoustic ranging signal is transmitted to the time the hydroacoustic ranging signal is received, and determines its own position according to the hydroacoustic time delay and sound velocity correction data; during the positioning process, regular time synchronization is performed between the anchored sonars 4 of each underwater base station, and between the user terminal 2 and the base station network.

[0062] The propagation time of underwater acoustic signals 6 contains not only distance information, but also the sound speed information of the signal propagation path. The ocean temperature, salinity and depth information can be used to construct the sound speed background field, and based on the relationship between the spatiotemporal variation of sound speed and the signal propagation time, the sound speed error tomographic inversion and correction method can be obtained, thereby providing refined sound speed error correction for regional underwater navigation positioning.

[0063] The generation and broadcasting of sound speed correction data includes the following steps:

[0064] (1) Calculate the sound speed using multi-source data, decompose the sound speed into spatial function and time function, and construct the sound speed background field, as follows:

[0065] Taking the existing regional ocean analysis data and the temperature, salinity and depth of the numerical forecast model as background field constraints, the measured data of the temperature, salinity and depth measuring instrument are added, and the multi-source data are fused to obtain the sound speed; according to the spatial distribution characteristics of the sound speed and the service area of ​​the base station network, the optimal boundary depth of the sound speed profile is analyzed; based on the depth, the layered empirical orthogonal function (EOF) decomposition is performed to decompose the sound speed into space function and time function; then the fitted time function and space function are used to represent the sound speed at any time and position, so as to realize the construction of the regional three-dimensional time-varying sound speed background field.

[0066] (2) Taking the constructed sound velocity background field as a priori value, taking the propagation delay data of the underwater acoustic ranging signal observed in real time by the anchored sonars 4 of each underwater base station as input, the propagation delay of the underwater acoustic ranging signal caused by the sound velocity error including the horizontal gradient is obtained;

[0067] The invention is based on the assumption of horizontal stratification of sound velocity variation, introduces the nadir total delay, and establishes the expression of vertical underwater acoustic ranging signal propagation delay error; considers the difference of sound signal propagation error in the horizontal direction, introduces the sound velocity horizontal gradient term, and establishes the gradient delay decomposition formula in the north and east directions; for the purpose of obtaining the delay error on the signal path, establishes a projection function based on parameters such as the sound line incident angle and azimuth, projects the vertical delay error and the horizontal gradient delay to the sound line direction, and constructs the projection function; takes the sound velocity background field constructed in step (1) as a priori value, takes real-time observation data (acoustic signal propagation time, base station location, etc.) as input, and estimates the sound velocity error of the additional sound velocity horizontal gradient.

[0068] The propagation delay of underwater acoustic ranging signal caused by sound speed error is expressed as:

[0069]

[0070]

[0071] M Δ (θ)=M(θ)tanθ=M(ε)cotε

[0072] Where δT is the propagation delay of the underwater acoustic ranging signal caused by the sound speed error, δT NTD , M(θ) are the total nadir delay and its projection function, G N , G E are the horizontal gradient terms in the north and east directions, M Δ (θ) is the projection function of the gradient term, θ and ε are the initial incident angle and initial grazing angle of the sound ray, respectively. is the azimuth.

[0073] (3) The propagation delay of the underwater acoustic ranging signal caused by the sound velocity error is used to construct the sound velocity error tomographic equation group, and the regional sound velocity error inversion is performed by adding constraints;

[0074] The present invention inverts the sound velocity error in the region, establishes an expression for the hydroacoustic time delay observation value and the slowness integral, integrates and discretizes the slowness based on the acoustic signal path, and constructs a sound velocity error tomographic equation group;

[0075] Analyze the acoustic signal coverage according to the state of the underwater base station 1 (static, dynamic, sea surface and underwater, etc.), and select a suitable grid model (such as a cuboid or an inverted cone, etc.) to represent the integration area;

[0076] The grid resolution is set based on the density of acoustic signals and the characteristics of sound velocity variation, a non-uniform grid model is constructed, and the integral path length of slowness is extracted to realize the coefficient matrix construction of the tomographic equation group.

[0077] Since the sound line cannot pass through all the grids, the tomographic equation group is ill-posed. The present invention adds a constraint equation to obtain a unique solution to the tomographic equation group. For example, a horizontal constraint relationship between the sound velocity error correction parameters in the same layer is established by distance weighted average or the like, the vertical change of the sound velocity is characterized by linear fitting or the like, and a vertical constraint equation is added by using a fitting polynomial. The sound velocity error is assigned an initial value and precision according to the sound velocity background field. Since the sound velocity change in the deep ocean tends to be stable, the sound velocity error value near the lower boundary of the grid can be constrained to be zero or a very small value.

[0078] The present invention combines constraint conditions and tomographic equations to solve the sound velocity error using equivalent weights; extracts the corrected sound velocity structure, and uses the measured sound velocity data as a reference to evaluate the accuracy and timeliness of the regional sound velocity.

[0079] The formula for regional sound velocity error inversion is as follows:

[0080] δs=1 / (v+δv)-1 / v

[0081]

[0082] In the formula, δs is the sound speed slowness error, v is the initial sound speed, δv is the sound speed error, δT j is the propagation delay of the underwater acoustic ranging signal due to the sound velocity error of the jth acoustic signal, (x, z, t) are the plane position, depth and time of the grid respectively, dl is the integral path of the acoustic signal, Γ is the total path, i is the sub-grid number that the acoustic signal passes through, i = 1, 2, 3, ..., n.

[0083] (4) Using the regional sound speed error obtained in the previous step and the sound speed reference customized by the base station system, generate and broadcast sound speed correction data.

[0084] The underwater base stations 1 of the present invention mutually transmit acoustic observation data, independently perform sound speed error estimation in a distributed manner, and correct and update the sound speed field. In order to improve data broadcasting efficiency and save transmission costs, the present invention adopts a sound speed correction product based on parameter reconstruction, and uses the sound speed result estimated in step (3) and the sound speed reference customized by the base station system to calculate the sound speed correction data of the regional grid (x, z, t), and establish a parameter expression of the sound speed correction number and the grid position. On this basis, each base station broadcasts the reconstructed parameter information.

[0085] The format of the sound speed correction product of the present invention mainly includes fields such as time, base station mark, location, sound speed correction reconstruction parameters and custom sound speed reference, and the data is encoded in sequence according to the grid space position and field definition order. Based on the timeliness of the sound speed data, each acoustic base station actively broadcasts the sound speed correction product to users within the regional range; after the terminal user passively receives the message broadcast by the base station, it decodes and obtains the sound speed correction product, and performs grid interpolation or extrapolation according to the user's approximate location information to obtain information such as sound speed correction. Based on the corrected sound speed, the terminal user can achieve high-precision position solution, clock error estimation, sound speed correction and other functions.

[0086] During the positioning process, the broadcast underwater positioning system needs to maintain high-precision clock synchronization between the anchor sonar 4 of the underwater base station and the user terminal 2.

[0087] Before deployment, the underwater base station 1 of the present invention generally uses an external accurate clock source (such as GNSS timing) to calibrate the clock deviation. After calibration, the clocks between multiple underwater base stations 1 can be considered to be strictly synchronized, with a deviation in the nanosecond order. However, with the accumulation of underwater time and environmental differences such as temperature and salinity, the clock deviation between different underwater base stations 1 will increase. In order to ensure the terminal positioning accuracy, it is necessary to correct the clock deviation between the underwater base stations 1 to achieve time synchronization between the underwater base stations.

[0088] The underwater base station 1 of the present invention is equipped with a high-precision chip-level atomic clock or a quartz clock, and can regularly perform joint measurement with the sea surface GNSS-acoustic timing to correct the base station clock drift and maintain an absolute time reference.

[0089] The underwater base stations 1 of the present invention perform regular joint measurement and self-correction of time synchronization deviation to maintain the underwater relative time reference. When the present invention performs time synchronization between underwater base stations 1, it can be considered that the underwater clock is stable in a short time, and the ocean current is relatively stable in a short time, and the position of the anchor sonar 4 of the underwater base station does not change in a short time.

[0090] The time synchronization between the moored sonars 4 of each underwater base station is achieved by two response measurements between the two moored sonars 4 and correction using the flow velocity and flow direction measured by the current meter 10. The specific method is as follows:

[0091] Anchored sonar A transmits a pulse signal, and anchored sonar B receives the pulse signal and processes it to obtain the time delay t B1 ; Then, the mooring sonar B responds with a pulse signal after the agreed delay Δd, and the mooring sonar A receives the pulse signal; Then, the mooring sonar A responds with a pulse signal again after the same agreed delay Δd, and the mooring sonar B receives the pulse signal. The time delay t between the sending and receiving of the two pulse signals by the mooring sonar B is calculated. B2 ;

[0092] Assume that the current correction is Δc. If there is no current observation, Δc = 0. Then the anchored sonar B can measure the t B1 and t B2 The synchronization time deviation ΔT between the anchored sonar B and the anchored sonar A is calculated as: ΔT = 0.5*(t B2 -Δd)+Δc-t B1 ; The anchored sonar B adjusts its own clock according to the synchronization time deviation ΔT to achieve time synchronization with the anchored sonar A;

[0093] The same method can be used to obtain the synchronization time deviation between other anchored sonars and anchored sonar A, and the same method can be used to obtain the synchronization time deviation between any two adjacent anchored sonars, and the synchronization deviation can be corrected to achieve precise time synchronization between all anchored sonars.

[0094] The time synchronization method between the user terminal 2 and the base station network is as follows:

[0095] The clock error model of user terminal 2 is described as a quadratic polynomial model:

[0096] Δt=a 0 +a 1 (tt oc )+a 2 (tt oc ) 2 ;

[0097] Where Δt is the clock difference between user terminal 2 and the base station network, t oc represents the starting reference time selected by the clock error model, a 0 、a 1 、a 2 are the clock deviation, clock speed and frequency drift parameters of the clock of the user terminal 2 respectively, and t is the time when the user terminal 2 receives the sound signal;

[0098] When user terminal 2 receives the base station network underwater acoustic ranging signal to determine its own position, the clock error Δt obtained by parameter estimation is substituted into the above formula to obtain a 0 、a 1 、a 2 When the user terminal 2 does not receive the underwater acoustic ranging signal from the base station network, the clock error Δt is predicted by the quadratic polynomial model to complete the time synchronization between the user terminal 2 and the base station network.

[0099] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A broadcast underwater navigation and positioning method, using a broadcast underwater navigation and positioning system, characterized in that: The navigation and positioning system includes a base station network composed of multiple underwater base stations distributed on the seabed and a user terminal to be positioned underwater, wherein the underwater base station includes a bottom-mounted sonar and an anchored sonar, the bottom-mounted sonar and the anchored sonar are connected by a cable, and use hydroacoustic signals for ranging and communication, the anchored sonar is integrated with an inertial measurement unit 1, and the user terminal is configured with a passive sonar, which unidirectionally receives the hydroacoustic signals emitted by the anchored sonar for ranging and communication; The navigation positioning method includes the following steps: Step 1: Use GNSS-acoustic ranging positioning technology to obtain the position coordinates of each bottom-mounted sonar; Step 2: The anchored sonar and the bottom-mounted sonar perform response measurement through hydroacoustic signals, and the position coordinates of the anchored sonar are calculated according to the time delay of the hydroacoustic signal measured by the anchored sonar and the observation value of the inertial measurement unit 1; Step 3: The anchored sonar generates and broadcasts the hydroacoustic ranging signal and the sound velocity correction data at a predetermined time interval. After the passive sonar of the user terminal receives the hydroacoustic ranging signal and the sound velocity correction data broadcast by the anchored sonar, it decodes and obtains the hydroacoustic delay and the sound velocity correction data from the time when the hydroacoustic ranging signal is transmitted to the time when the hydroacoustic ranging signal is received, and determines its own position according to the hydroacoustic delay and the sound velocity correction data. During the positioning process, the anchored sonars of each underwater base station and the user terminal and the base station network are synchronized regularly. The method for generating sound speed correction data includes the following steps: (1) Calculate the sound speed using multi-source data, decompose the sound speed into spatial function and time function, and construct the sound speed background field; (2) Using the constructed sound velocity background field as a priori value and the propagation delay data of the underwater acoustic ranging signal observed in real time by the anchored sonars of each underwater base station as input, the propagation delay of the underwater acoustic ranging signal caused by the sound velocity error containing the horizontal gradient is obtained; (3) Using the propagation delay of the underwater acoustic ranging signal caused by the sound velocity error, a group of sound velocity error tomographic equations is constructed, and the regional sound velocity error inversion is performed by adding constraints; (4) Generate sound speed correction data using the regional sound speed error obtained in the previous step and the sound speed reference customized by the base station system.

2. A broadcast underwater navigation and positioning method according to claim 1, characterized in that: The anchored sonar is also integrated with a temperature-salinity-depth measuring instrument, a pressure gauge and a current meter, and the user terminal is also equipped with an inertial measurement unit 2.

3. A broadcast underwater navigation and positioning method according to claim 1, characterized in that: In the step 2, the position coordinates of the moored sonar are calculated by using data measured by a temperature, salinity and depth measuring instrument, a pressure gauge and a current meter integrated on the moored sonar.

4. A broadcast underwater navigation and positioning method according to claim 1, characterized in that: The time synchronization between the moored sonars of each underwater base station is achieved through two response measurements between the two moored sonars, and the flow velocity and direction measured by the current meter are used for correction. The specific method is as follows: Anchored sonar A transmits a pulse signal, and anchored sonar B receives the pulse signal and processes it to obtain the time delay. ; Then, the moored sonar B is Then it responds with a pulse signal, and the anchor sonar A receives the pulse signal; Then, the moored sonar A is Then it responds with a pulse signal again. The anchor sonar B receives the pulse signal and processes it to obtain the time delay between the two pulse signals sent and received by the anchor sonar B. ; Assume that the ocean current correction is If there is no ocean current observation, , then the anchored sonar B is based on the measured and Calculate the synchronization time deviation between anchored sonar B and anchored sonar A for: ; Anchored sonar B according to the synchronization time deviation Adjust its own clock to synchronize with the anchored sonar A; The same method can be used to obtain the synchronization time deviation between other anchored sonars and anchored sonar A, and the same method can be used to obtain the synchronization time deviation between any two adjacent anchored sonars, and the synchronization deviation can be corrected to achieve precise time synchronization between all anchored sonars.

5. The method for underwater navigation and positioning according to claim 1, characterized in that: The time synchronization method between the user terminal and the base station network is as follows: The clock error model of the user terminal is described as a quadratic polynomial model: ； In the formula, is the clock difference between the user terminal and the base station network, represents the starting reference time selected by the clock error model, , , are the clock deviation, clock speed and frequency drift parameters of the user terminal clock respectively. The time when the user terminal receives the sound signal; When the user terminal receives the base station network's underwater acoustic ranging signal to determine its own position, the clock error obtained by parameter estimation is Substituting into the above formula, we can get , , When the user terminal does not receive the base station network hydroacoustic ranging signal, the clock error is predicted by the quadratic polynomial model , complete the time synchronization between the user terminal and the base station network.

6. A broadcast underwater navigation and positioning method according to claim 1, characterized in that: Step (1) The method for constructing the sound velocity background field is as follows: using the existing regional ocean analysis data and the temperature, salinity and depth of the numerical forecast model as background field constraints, adding the measured data of the temperature, salinity and depth measuring instrument integrated on the anchored sonar, and fusing the multi-source data to obtain the sound velocity; analyzing the optimal boundary depth of the sound velocity profile based on the spatial distribution characteristics of the sound velocity and the service area of ​​the base station network; performing layered empirical orthogonal function decomposition based on the depth, and decomposing the sound velocity into a spatial function and a time function; then using the fitted time function and space function to represent the sound velocity at any time and position, to realize the construction of a regional three-dimensional time-varying sound velocity background field.

7. A broadcast underwater navigation and positioning method according to claim 1, characterized in that: In step (2), the propagation delay of the underwater acoustic ranging signal caused by the sound speed error is expressed as: ； ； ； In the formula, is the propagation delay of underwater acoustic ranging signal caused by sound speed error, , are the total nadir delay and its projection function, , are the horizontal gradient terms in the north and east directions, is the projection function of the gradient term, , are the initial incident angle and initial grazing angle of the sound ray, respectively. is the azimuth.

8. The method for underwater navigation and positioning according to claim 1, characterized in that: The formula for inversion of regional sound velocity error in step (3) is as follows: ； ； In the formula, is the sound speed slowness error, is the initial sound speed, is the sound velocity error, For the The propagation delay of the underwater acoustic ranging signal caused by the sound velocity error of the sound signal, are the plane position, depth and time of the grid respectively, is the acoustic signal integration path, is the total path, is the sub-grid number that the sound signal goes through, .

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