High-precision measurement method for radial speed of shallow sea underwater acoustic target based on ray sound field reconstruction

Abstract

The invention relates to the technical field of communication, and discloses a high-precision measurement method for radial velocity of a shallow sea underwater acoustic target based on ray sound field reconstruction. According to the method, a multipath channel joint resolving system is innovatively constructed for the problem that the target speed measurement precision is limited due to a shallow sea complex propagation environment. According to the system, a compound ray model of shallow sea multipath sound propagation is established, and a joint representation equation containing channel impulse response and target motion parameters is constructed by analyzing a time delay-Doppler coupling mechanism of three typical paths of direct waves, water surface reflected waves and water bottom reflected waves. Especially for the multipath interference effect in the shallow sea waveguide environment, the time-frequency domain separation criterion of each path signal is deduced, and a theoretical basis is laid for feature information extraction. The method provides a new technical means for underwater target tracking and positioning, underwater acoustic communication Doppler compensation and marine environment dynamic monitoring, and particularly has an important application prospect in the fields of underwater unmanned cluster collaboration and the like.

Description

Technical Field

[0001] The present invention relates to the field of communication technology, and in particular to a high-precision radial velocity measurement method for shallow sea water acoustic targets by reconstructing ray acoustic fields. Background Art

[0002] Radial velocity measurement of underwater targets is one of the core technologies in the field of ocean detection. Traditional methods are mainly based on the principle of Doppler effect, but face severe challenges in the shallow sea multipath propagation environment. Existing technologies have the following systematic defects: 1. Physical limitations of the single-path model: The current mainstream method is based on the free-field assumption and only considers direct sound propagation. However, sound wave propagation in shallow water environments presents significant multipath characteristics: the surface reflection path is affected by sea waves and produces time-varying phase disturbances (RMS phase error can reach 30°); the seabed reflection path leads to uncertainty in reflection coefficients (typical error ±0.15) due to the acoustic impedance mismatch of the sediment layer.

[0003] 2. Error transmission caused by time-varying channels: Algorithms under the traditional static channel assumption face the problem of adaptability to dynamic environments: delay jitter (wave motion causes fluctuations in sound path delay, with a root mean square error of up to 0.1Tc), Doppler spread (the movement of the carrier platform causes the Doppler spectrum to broaden, with a typical broadening factor of 1.2-1.8), and parameter coupling (changes in the sound velocity profile affect both delay and Doppler calculations).

[0004] Therefore, the existing technology has not effectively solved the three core contradictions in the shallow sea multipath environment: ① the characterization mismatch between complex propagation physics and simplified channel models; ② the bottleneck between multipath coupling effects and insufficient signal processing dimensions; ③ the adaptability gap between dynamic environmental changes and static parameter assumptions. This directly leads to the performance indicators (accuracy, robustness, and environmental adaptability) of current underwater speed measurement equipment in shallow sea areas being difficult to meet actual engineering needs.

[0005] Therefore, it is necessary to provide a high-precision measurement method for the radial velocity of shallow water acoustic targets by reconstructing the ray acoustic field to solve the above technical problems. Summary of the invention

[0006] In order to solve the technical problem of limited target velocity measurement accuracy caused by complex propagation environment in shallow waters, the present invention provides a high-precision radial velocity measurement method for shallow water acoustic targets by reconstructing ray acoustic fields, which is suitable for scenarios such as underwater vehicle navigation and marine environment monitoring that require accurate velocity measurement of underwater targets.

[0007] The method for high-precision measurement of radial velocity of shallow sea water acoustic target by ray acoustic field reconstruction provided by the present invention includes the following schemes: The present invention proposes a target radial velocity measurement method based on ray acoustic field reconstruction, and its technical solution includes: (1) Establish a three-path propagation model including direct, water surface reflection, and seabed reflection In the channel modeling of a typical shallow water environment, this study simplifies the sound propagation into a single reflection process, ignores the high-order reflection effect, and adopts the straight-line propagation and mirror reflection assumptions. When constructing the observation system, the following definition is made: The motion vector parameter of the receiver RX (passive sonar) is the velocity , the counterclockwise angle between the movement direction and the vertical reference line ; The motion vector parameter of the transmitter TX (underwater target) is the speed , the clockwise angle between the movement direction and the vertical reference line . Special provisions for the relative motion direction of the two platforms: When the two are opposite, they are moving towards each other; when the two are opposite, they are moving away from each other.

[0008] Based on the above kinematic characteristics and propagation constraints, this study established a three-path propagation model including direct wave (DP), surface primary reflection wave (SRP), and bottom primary reflection wave (BRP). The physical characteristics of each path can be expressed as: Direct path: The sound wave propagates in a straight line between RX and TX, satisfying the spherical wave attenuation law; for a direct sound line, the sound wave propagates directly from the emission point to the target point. The propagation path length and propagation time can be calculated by the sound velocity profile and the target position coordinates. The Doppler frequency shift caused by the target motion is related to the angle between the radial velocity of the target and the propagation direction of the sound line.

[0009] Water surface reflection path: Sound waves are reflected from the sea-air interface, following the pressure release boundary condition, and the reflection coefficient is approximately -1; the propagation path of the sound line reflected from the water surface includes the incident segment from the sound source to the water surface and the reflection segment from the water surface to the target. Its propagation path length and propagation time can be calculated through the geometric relationship of water surface reflection. The Doppler frequency shift of the sound line reflected from the water surface is also related to the angle between the radial velocity of the target and the propagation direction of the sound line.

[0010] Seabed reflection path: Sound waves are reflected by the sediment layer, and the reflection coefficient is determined by the acoustic impedance characteristics of the seabed. The propagation path of the underwater reflected sound line includes the incident section from the sound source to the bottom of the water and the reflection section from the bottom of the water to the target. Its propagation path length and propagation time can be calculated through the geometric relationship of the bottom reflection. The Doppler frequency shift of the underwater reflected sound line is also related to the angle between the radial velocity of the target and the propagation direction of the sound line.

[0011] The model calculates the propagation delay of each path through ray tracing method. and phase shift , (1) in is the geometric propagation distance of the ith path, c is the weighted value of the sound velocity profile, Characterizes the Doppler time shift caused by motion, The model includes the phase mutation introduced by boundary reflection. The model takes into account the multipath interference effect unique to shallow water environment and reveals the time-varying characteristics of the channel impulse response through path delay difference analysis.

[0012] (2) Constructing a multi-constrained Doppler frequency shift equation group for velocity calculation The core idea of ​​constructing a multi-constrained Doppler frequency shift equation group for velocity calculation is to use the Doppler frequency shift information of multiple sound line propagation paths, combined with the frequency shift law caused by target motion, to establish an equation group containing multiple constraints, and adopt an iterative optimization method to continuously adjust the estimated value of the target radial velocity to make it meet the Doppler frequency shift constraints of all sound lines. At the same time, combined with environmental parameters such as the sound velocity profile and water depth in the shallow sea environment, the accuracy and robustness of the solution are further improved, thereby achieving high-precision solution of the target radial velocity.

[0013] Assume the frequency of the transmitted signal is The Doppler frequency shift observation value of the received signal on the i-th path is ,satisfy: (2) in is the unit vector of the propagation direction of the i-th path, is the target velocity vector (polar coordinate decomposition), is the velocity vector of the sonar platform.

[0014] Assuming that the Doppler frequency shifts of the three paths have been measured through signal processing, the equation group is established: (3) Among them, the sea surface reflection path , seabed reflection path , is the modulus of the seabed reflection coefficient.

[0015] The optimal estimate of the target radial velocity is achieved by solving the following minimization problem: (4) in N Indicates the number of multipaths, represents the Doppler shift observed on the i-th path, is the equivalent angle of incidence, is the environmental disturbance compensation term, is the L1 regularization weight factor.

[0016] The technical innovation of this method is mainly reflected in three dimensions: ① A spatiotemporal joint characterization model of multipath sound rays was constructed, which broke through the limitations of the traditional single-path model by quantifying the coupling relationship between the propagation delay and Doppler frequency shift of different paths; ② Developed a multipath separation algorithm based on the fractional Fourier transform of HFM signals, and realized multipath signal identification under complex channel conditions by taking advantage of its sharp autocorrelation peak and high Doppler tolerance. ③ A propagation delay compensation method based on ray tracing is proposed, and the influence of multipath effect on velocity solution is eliminated through an iterative optimization algorithm.

[0017] This progress provides new technical means for underwater target tracking and positioning, Doppler compensation in underwater acoustic communications, and dynamic monitoring of the marine environment, and has important application prospects, especially in the fields of underwater unmanned cluster collaboration.

[0018] Compared with the related art, the high-precision radial velocity measurement method of shallow sea water acoustic target by ray acoustic field reconstruction provided by the present invention has the following beneficial effects: 1. Innovative design of integrated communication and perception signal waveform: A underwater acoustic communication and perception integrated waveform based on hyperbolic frequency modulation (HFM) signal is proposed to achieve deep integration of underwater target radial velocity estimation and communication functions. By optimizing the signal carrier frequency characteristics and bandwidth range, the problem of mutual interference between communication and perception functions in traditional methods is solved, and the system spectrum utilization efficiency is significantly improved. Simulation results show that the waveform can simultaneously extract target motion information while maintaining communication rate and reliability.

[0019] 2. Accuracy breakthrough under the multipath sound ray model: Breaking through the limitations of the traditional direct sound ray model, an innovative three-dimensional sound propagation theoretical framework including direct sound rays, surface reflected sound rays, and bottom reflected sound rays is constructed. Simulation results show that the accuracy of the multipath joint solution is 2-3 times higher than that of the single direct sound ray model, especially under complex hydrological conditions (such as thermocline and bottom reflection coefficient fluctuations).

[0020] 3. Dynamic environment adaptive matching mechanism: A dynamic optimization selection algorithm for sound propagation paths is proposed. By analyzing the signal carrier frequency characteristics (5-30 kHz), bandwidth range (1-10 kHz) and the relative motion state of the transceiver (0-15 knots) in real time, the optimal sound line combination model is matched autonomously. This mechanism can adapt to the time-varying characteristics of different marine environmental parameters (sound velocity profile, bottom type), and its robustness to dynamic scenes has been verified in simulation and tank tests.

[0021] 4. Frequency domain complementary characteristics enhance system robustness: reveal the complementary characteristics of the multipath model and the direct sound ray model in different frequency bands: in the low frequency band (0-2 kHz), the multipath model enhances signal stability through phase interference; in the high frequency band (5-20kHz), the direct sound ray model relies on the delay resolution advantage of broadband signals. Through the frequency band adaptive switching mechanism, the system can maintain the continuity of velocity estimation under complex channel conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the signal propagation path in a high-precision measurement method of radial velocity of shallow water acoustic targets by ray acoustic field reconstruction provided by the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0024] The method for high-precision radial velocity measurement of shallow sea water acoustic targets by ray acoustic field reconstruction proposed by the present invention comprises the following steps: Step 1: The PC generates an up-and-down sweep HFM signal as a preamble integrated communication sensing signal and transmits it in the underwater acoustic channel in the form of sound waves through the transmitting transducer. The matching peak interval between the up-and-down sweep HFM signal and the down-and-up sweep HFM signal at the transmitting end is .

[0025] Step 2: The receiving transducer intercepts the acoustic wave signal and uses the excellent autocorrelation characteristics of the hyperbolic frequency modulation signal to make it of great value in signal synchronization: its autocorrelation function presents an approximate pulse-like feature, and by analyzing the time domain scale difference between the time domain correlation peaks of the receiving end and the transmitting end (manifested as compression or expansion of the time interval between the matching peaks), the speed estimation of the moving target is achieved. At this time, the matching peak interval between the corresponding up-scanning HFM signal and the down-scanning HFM signal becomes: (5) The change in the matching peak between the up-scan HFM signal and the down-scan HFM signal caused by the Doppler effect is .

[0026] Step 3: This article assumes , from which the estimated Doppler compression or expansion factor is (6) The final estimated radial velocity of the moving target can be expressed as (7).

[0027] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A high-precision measurement method for radial velocity of shallow water acoustic targets by ray acoustic field reconstruction, characterized in that: The following steps are involved: A three-path propagation model including direct wave, water surface reflected wave and seabed reflected wave is established. The model calculates the propagation delay and phase shift of each path by ray tracing method and takes into account the multipath interference effect unique to shallow water environment. A multi-constrained Doppler frequency shift equation group is constructed to solve the velocity. The equation group uses the Doppler frequency shift information of multiple sound ray propagation paths, combines the frequency shift law caused by target motion, and adopts an iterative optimization method to solve the target radial velocity.

2. The high-precision measurement method for radial velocity of shallow water acoustic targets by ray acoustic field reconstruction according to claim 1 is characterized in that: In the path propagation model: Direct path: The sound wave propagates along a straight line between the receiving end and the transmitting end, satisfying the spherical wave attenuation law; Water surface reflection path: The sound wave is reflected by the sea-air interface, and the reflection coefficient is approximately -1. Its propagation path includes the incident segment from the sound source to the water surface and the reflection segment from the water surface to the target; Seabed reflection path: The sound wave is reflected by the sediment layer, and the reflection coefficient is determined by the acoustic impedance characteristics of the seabed. Its propagation path includes the incident section from the sound source to the water bottom and the reflection section from the water bottom to the target.

3. The high-precision measurement method for radial velocity of shallow water acoustic targets by ray acoustic field reconstruction according to claim 1 is characterized in that: The propagation delay and phase shift , ， in is the geometric propagation distance of the ith path, c is the weighted value of the sound velocity profile, Characterizes the Doppler time shift caused by motion, Includes phase jumps introduced by boundary reflections.

4. The high-precision measurement method for radial velocity of shallow water acoustic targets by ray acoustic field reconstruction according to claim 1 is characterized in that: The Doppler frequency shift observation of the received signal on the i-th path is ,satisfy: in, is the transmitting signal frequency, is the unit vector of the propagation direction of the i-th path, is the target velocity vector, is the velocity vector of the sonar platform.

5. The high-precision measurement method for radial velocity of shallow water acoustic targets by ray acoustic field reconstruction according to claim 1 is characterized in that: The Doppler frequency shift equations for the three paths are: (3) Among them, the sea surface reflection path , seabed reflection path , is the modulus of the seabed reflection coefficient.

6. The high-precision radial velocity measurement method of shallow water acoustic target by ray acoustic field reconstruction according to claim 1 is characterized in that: The optimal estimation of the target radial velocity is achieved by solving the following minimization problem: Where N represents the number of multipaths, represents the Doppler shift observed on the i-th path, is the equivalent angle of incidence, is the environmental disturbance compensation term, is the L1 regularization weight factor.

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