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, in particular to a high-precision measurement method for radial velocity of a shallow sea underwater acoustic target based on ray sound field reconstruction, which comprises the following steps of: establishing a three-path propagation model comprising direct arrival, water surface reflection and seabed reflection, and constructing a joint representation equation comprising channel impulse response and target motion parameters by the path propagation model; according to the method, a space-time joint representation model of multipath sound rays is constructed, and the limitation of a traditional single-path model is broken through by quantifying the coupling relation between propagation time delay and Doppler frequency shift of different paths; the development provides a new technical means for underwater target tracking and positioning, underwater acoustic communication Doppler compensation and marine environment dynamic monitoring, and especially has an important application prospect in the fields of underwater unmanned cluster collaboration and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of communication technology, in particular to a shallow water acoustic target radial velocity high-precision measurement method based on ray sound field reconstruction. BACKGROUND

[0002] Underwater target radial velocity measurement is one of the core technologies in the field of ocean exploration. The traditional method is mainly based on the principle of Doppler effect, but it faces severe challenges in the shallow water multipath propagation environment. The existing technology has the following systematic defects:

[0003] 1. Physical limitations of single-path model: the current mainstream method is based on the free-field assumption, only considering direct sound propagation. However, in shallow water environment, sound propagation presents significant multipath characteristics: water surface reflection path: time-varying phase disturbance caused by sea surface wave (RMS phase error up to 30°) seabed reflection path: reflection coefficient uncertainty caused by sediment layer acoustic impedance mismatch (typical error ±0.15).

[0004] 2. Error transmission caused by time-varying channel: algorithms based on traditional static channel assumption face dynamic environment adaptability problems: time delay jitter: sound path time delay fluctuation caused by wave motion; Doppler spread: Doppler spectrum broadening caused by carrier platform motion; parameter coupling: sound speed profile changes affect both time delay and Doppler calculation

[0005] Therefore, the existing technology has not effectively solved the three core contradictions in the shallow water multipath environment: 1. Representation mismatch between complex propagation physics and simplified channel model; 2. Solving bottleneck between multipath coupling effect and insufficient signal processing dimension; 3. Adaptability gap between dynamic environment changes and static parameter assumption. This directly leads to the performance indicators (precision, robustness, environmental adaptability) of current underwater velocity measurement equipment in shallow water area difficult to meet the actual engineering needs. SUMMARY

[0006] The purpose of the present application is to provide a shallow water acoustic target radial velocity high-precision measurement method based on ray sound field reconstruction, which includes establishing a three-path propagation model containing direct, water surface reflection and seabed reflection, the path propagation model constructs a joint representation equation containing channel impulse response and target motion parameters; constructing a multi-constrained Doppler shift equation set for velocity solving, the Doppler shift equation set is based on different sound path combination forms, and the joint estimation of Doppler factor and signal arrival time is realized to realize the fusion of velocity perception and signal synchronization function.

[0007] In typical shallow water environment channel modeling, this study simplifies sound propagation as a one-time reflection process, ignoring high-order reflection effects, and adopts straight-line propagation and mirror reflection assumption. When constructing the observation system, define: the motion vector parameter of the receiving end RX (passive sonar) is velocity V R, the angle θ between the moving direction and the vertical reference line r ; the motion vector parameter of the transmitting end TX (underwater target) is velocity V T , the angle θ between the moving direction and the vertical reference line t The relative motion direction criterion of the two platforms is particularly specified: when (V R cosβ2+V T cosα2)>0, it is a relative motion state, otherwise, it is a back motion state.

[0008] Preferably, the path propagation model comprises:

[0009] Direct path: the sound wave propagates along the straight line between RX and TX, and follows the full-sphere wave attenuation law; for the direct sound line, the sound wave directly propagates from the transmitting point to the target point. The propagation path length and the propagation time can be calculated by the sound speed profile and the target position coordinates. The Doppler 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;

[0010] Surface reflection path: the sound wave is reflected by the sea-air interface, and follows the pressure release boundary condition, and the reflection coefficient is approximately -1; the propagation path of the surface reflection sound line includes the incident segment from the sound source to the water surface and the reflection segment from the water surface to the target. The propagation path length and the propagation time can be calculated by the surface reflection geometric relationship. The Doppler shift of the surface reflection sound line is also related to the angle between the radial velocity of the target and the propagation direction of the sound line;

[0011] Bottom reflection path: the sound wave is reflected by the sediment layer, and the reflection coefficient is determined by the acoustic impedance characteristics of the sea bottom. The propagation path of the bottom reflection sound line includes the incident segment from the sound source to the water bottom and the reflection segment from the water bottom to the target. The propagation path length and the propagation time can be calculated by the bottom reflection geometric relationship. The Doppler shift of the bottom reflection sound line is also related to the angle between the radial velocity of the target and the propagation direction of the sound line.

[0012] The propagation distances {D1, D2, D3} of the direct sound path, the surface reflection sound path and the bottom reflection sound path are respectively

[0013]

[0014] Therefore, the time delays of the respective paths are respectively In view of the absorption effect in the underwater acoustic channel, the absorption loss amplitude attenuation coefficient of the underwater acoustic signal is where R represents the sound path propagation distance, and a is the seawater absorption loss. The extended loss amplitude attenuation coefficient at a distance of L from the TX is The bottom reflection coefficient r b , and the surface reflection coefficient r s . Therefore, the direct sound path factor is water surface reflection factor water bottom reflection factor The negative sign indicates that the phase generates a reversal,

[0015] Preferably, the joint representation equation deduces the time-frequency domain separation criterion of each path signal for the multipath interference effect in the shallow sea waveguide environment.

[0016] Preferably, the Doppler shift equation set includes the sea surface reflection path and the sea bottom reflection path.

[0017] Compared with the prior art, the beneficial effects of the present application are:

[0018] 1. Precision breakthrough under the multi-path sound ray model: Break through the limitation of the traditional direct sound ray model, and innovatively construct a three-dimensional sound propagation theoretical framework including direct sound ray, water surface reflection sound ray and water bottom reflection sound ray. Simulation results show that the precision is improved by 2-3 times through multi-path joint solution compared with single direct sound ray model, especially under complex hydrological conditions (such as thermocline, bottom reflection coefficient fluctuation).

[0019] 2. Dynamic environment adaptive matching mechanism: A dynamic optimization selection algorithm of sound propagation path is proposed, which can autonomously match the optimal sound ray combination model by real-time analyzing the signal carrier frequency characteristics (5-30kHz), bandwidth range (1-10kHz) and relative motion state (0-15 knots) of the transmitting and receiving device. This mechanism can adapt to the time-varying characteristics of different marine environmental parameters (sound speed profile, bottom type), and its robustness to dynamic scenes is verified in simulation and pool test.

[0020] 3. Frequency domain complementary characteristics enhance system robustness: The complementary characteristics of multi-path model and direct sound ray model in different frequency bands are revealed: in the low frequency band (0-2kHz), the multi-path model enhances the signal stability through phase interference; in the high frequency band (5-20kHz), the direct sound ray model relies on the advantage of wideband signal time delay resolution. Through the frequency adaptive switching mechanism, the system can maintain the continuity of speed estimation under complex channel conditions. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The figure is a schematic diagram of the signal propagation path in the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application.

[0023] Reference Figure 1 The application discloses a shallow water acoustic target radial velocity high-precision measurement method for a ray sound field reconstruction.

[0024] Step 1: A PC end generates an up-sweep HFM signal and a down-sweep HFM signal as a communication and sensing integrated signal of a preamble and transmits the signals in a form of an acoustic wave in an underwater acoustic channel through a transmitting transducer, so that a matching peak interval between the up-sweep HFM signal and the down-sweep HFM signal at the transmitting end is T TX .

[0025] Step 2: A receiving transducer intercepts the acoustic wave signal, and the excellent autocorrelation characteristics of the hyperbolic frequency modulation signal have important values in signal synchronization: the autocorrelation function presents an approximate pulse-shaped feature, and the time interval between the matching peaks is compressed or expanded by analyzing the time domain scale difference between the time domain correlation peaks of the receiving end and the transmitting end, so that the velocity estimation of the moving target is realized. At this time, the matching peak interval between the corresponding up-sweep HFM signal and down-sweep HFM signal is changed to

[0026]

[0027] The change amount of the matching peak between the up-sweep HFM signal and the down-sweep HFM signal caused by the Doppler effect is T Δ = T RX -T TX .

[0028] Step 3: It is assumed in the present application that When the acoustic path through the water surface reflection is considered, the process is divided into two steps: in the first step, the velocity of the receiving end is projected on the acoustic path through the water surface reflection, The projection on the water surface reflection acoustic path is , and the angle between the water surface reflection acoustic path and the vertical direction is recorded as , The projection on the acoustic path through the water surface reflection is , and the angle between the acoustic path through the water surface reflection and the vertical direction is recorded as , and the included angle between the two is There are (5) This section introduces a mirror virtual source of the transmitting end, so that the water surface reflection point is the intersection point of the MVS and the receiving end straight line and the water surface. The time delay-Doppler joint characteristic quantity between the MVS introduced by the model and the receiving end will produce an observable parameter offset , and the following steps are used to estimate the radial velocity estimation component of the transmitting end (6) (7) Second step The projection on the water surface reflection path close to the transmitter is , and the included angle between them is denoted as , according to the model geometric relationship shown in Figure 1 , we can get (8) The change between the matching peak value of the projection imaginary point and the transmitter is , and the radial velocity estimation component of the transmitter in step two is written as (9) (10) Where , Essentially, they are all the results of the projection of each velocity component under the action of each reflection angle. Considering the velocity estimation results of the direct path and the water surface reflection path .

[0037] V direct+surface = χV direct + γ(V surface1 + V surface2 ). (11)

[0038] Where

[0039] Step 4: When considering the water bottom reflection path, the projection of V R in the water bottom reflection path direction is V R,X3 , and the angle between the water bottom reflection path and the vertical direction is denoted as β 3,2 , then we have

[0040] V R,X3 = V R cos(β3-β2), (12)V R,X3 The projection on the water bottom reflection path close to the transmitter is V R,X3,X , and the included angle is denoted as γ 3,X , and the angle between the water bottom reflection path close to the transmitter and the vertical direction in the clockwise direction is denoted as α3, we can get

[0041] V R,X3,X = V R,X3 cos(α3+β3-π), (13)

[0042] Consideration of water bottom reflected and direct path range dependent velocity estimation results

[0043] V direct+bottom = κV direct + η(V bottom1 + V bottom2 ). (14)

[0044] wherein

[0045] The above description is further detailed in conjunction with the specific embodiments of the present application, and the specific embodiments of the present application cannot be deemed to be limited to these descriptions. For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made, and all of these should be deemed to fall within the protection scope defined by the claims submitted in the present application.

Claims

1. A method for high-precision measurement of radial velocity of a shallow-water acoustic target by ray sound field reconstruction, characterized in that: The method comprises the following steps: A three-path propagation model including direct, water surface reflection and seabed reflection is established, and the path propagation model establishes a joint representation equation including channel impulse response and target motion parameters; A multi-constraint Doppler shift equation group is constructed for velocity solution, and the multi-constraint Doppler shift equation group is based on different sound path combination forms, joint estimation of a Doppler factor and signal arrival time, so that the fusion of velocity sensing and signal synchronization functions is realized.

2. The method of claim 1, wherein the method is a high-precision measurement method of radial velocity of a shallow-water acoustic target by ray sound field reconstruction. The path propagation model comprises: A direct path: sound waves propagate along a straight line between RX and TX, and the sound waves follow the law of full water surface wave attenuation; A water surface reflection path: sound waves are reflected by the sea-air interface, follow the pressure release boundary condition, and the reflection coefficient is approximately -1, and the propagation path length and propagation time can be calculated through the water surface reflection geometric relationship; A 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 bottom, and the propagation path length and propagation time can be calculated through the water bottom reflection geometric relationship.

3. The method of claim 1, wherein the method is a high-precision measurement method of radial velocity of a shallow-water acoustic target by ray sound field reconstruction. The propagation distances {D1, D2, D3} of the direct sound path, the water surface reflection sound path and the water bottom reflection sound path are respectively Therefore the path delays are τ D1 =D1 / c, τ D2 =D2 / c, τ D3 =D3 / c, for the absorption effect in the underwater acoustic channel, the underwater acoustic signal absorption loss amplitude attenuation coefficient where R represents the acoustic path propagation distance, a is the seawater absorption loss, and a is the spread loss amplitude attenuation coefficient at a distance of L from TX The water bottom reflection coefficient r b , the water surface reflection coefficient r s , then the direct acoustic path factor The water surface reflection factor The water bottom reflection factor The negative sign indicates that the phase is reversed, 4. The method of claim 1, wherein the method is a high-precision measurement method of radial velocity of a shallow-water acoustic target by ray sound field reconstruction. The joint representation equation derives a time-frequency domain separation criterion for multi-path interference effects in a shallow sea waveguide environment.

5. The method of claim 1, wherein the method is a high-precision measurement method of radial velocity of a shallow-water acoustic target by ray sound field reconstruction. The multi-constraint Doppler shift equation group includes a sea surface reflection path and a seabed reflection path.

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