Construction method of bistatic sonar self-interference signal simulation platform in time-varying marine environment

Abstract

The invention provides a method for constructing a bistatic sonar self-interference signal simulation platform in a time-varying marine environment, and solves the technical problems of high cost, long period and high safety risk due to the fact that an existing marine field test is easily influenced by weather and sea conditions. The method comprises the following steps: constructing a three-dimensional dynamic sea surface, an interface scattering model and a sea surface bubble model, respectively calculating interface scattering intensity and bubble cloud scattering intensity, constructing a unit scattering model, and performing unit division on a scatterer of the sea surface of the seabed to obtain a reverberation time sequence; constructing an ocean noise model and a target scattering characteristic model; and constructing a channel structure, correcting a time-varying channel by adopting a path management method to obtain a direct wave signal and a target echo signal, and superposing the direct wave signal, the target echo signal, the reverberation time sequence and the ocean noise model to obtain a receiving signal of a receiving station of the bistatic sonar target detection system. The method can be widely applied to the technical field of underwater acoustic engineering.

Description

Technical Field

[0001] This application belongs to the field of underwater acoustic engineering technology, and more specifically, it relates to a method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment. Background Technology

[0002] In the development of bistatic sonar target detection technology, field trials at sea are a traditional and core testing method. Conducting various tests in a real marine environment provides reliable data support for the technology's development and optimization, and is a crucial step in testing bistatic sonar detection technology.

[0003] However, traditional marine field tests are highly susceptible to weather changes and sea state fluctuations, leading to interruptions and compromising the continuity and stability of the testing process. Furthermore, marine field tests often involve high costs and lengthy testing cycles, making it difficult to meet the demands for rapid iteration and efficient system development in bistatic sonar technology. Simultaneously, the complexity and uncertainty of the marine environment can bring numerous unforeseen safety risks and economic losses, severely hindering the development of bistatic sonar detection technology. Summary of the Invention

[0004] The purpose of this application is to provide a method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment, so as to solve the technical problems of existing marine field tests being easily affected by weather and sea conditions, having high costs, long cycles, and high safety risks.

[0005] To achieve the above objectives, this application provides a method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment, comprising the following steps: A three-dimensional dynamic sea surface is constructed based on the JONSWAP spectrum and SWAP direction spectrum; An interface scattering model and a sea surface bubble model were constructed to calculate the interface scattering intensity and the bubble cloud scattering intensity, respectively. Combining the interface scattering intensity and the bubble cloud scattering intensity, a unit scattering model was constructed to divide the scatterers on the seabed and sea surface into units, thereby obtaining the reverberation time series. A marine noise model is constructed by combining turbulent pressure fluctuation noise, shipping noise, wind noise, rain noise, and thermal noise; a target scattering characteristic model is constructed based on sound scattering theory. Based on the Bellhop ray acoustic model, a channel structure is constructed, and the time-varying channel is corrected using the path management method to obtain the direct wave signal and the target echo signal. The direct wave signal, the target echo signal, the reverberation time series, and the ocean noise model are superimposed to obtain the received signal of the bistatic sonar target detection system receiving station.

[0006] Preferably, the process of correcting time-varying channels using path management methods includes: Based on the number of reflections from the sea surface and the seabed, sound rays are classified into types, output matrices are assigned to each type, and type ranges are set. The initial vocal parameters are stored in the output matrix, the time delay of the initial vocal parameters is extracted, and a time delay dictionary is constructed. Lock the corresponding type range in the output matrix according to the ray type, complete the path matching and ray parameter update according to the time delay matching threshold, allocate the free slots in the type range as new paths for unmatched ray types, perform virtualization operation on the disappeared paths, retain the time delay setting maximum loss, and correct the time-varying channel.

[0007] Preferably, the channel structure includes a direct wave channel H1, a target echo channel H2, a target scattering characteristic model, and a target echo channel H3; The transmitted signal is transmitted through the direct wave channel H1 to obtain the direct wave signal; The transmitted signal is transmitted through the target echo channel H2 to obtain the target incident wave, which is then input into the target scattering characteristic model to obtain the target scattered wave. Finally, the target scattered wave is input into the target echo channel H3 to obtain the target echo.

[0008] Preferably, the process of constructing a target scattering characteristic model includes: Determine the target's geometric characteristics, material acoustic parameters, surrounding medium acoustic parameters, and incident wave conditions; For a spherical target, the total velocity potential is expanded into a basis function in spherical coordinates based on the Helmholtz equation. The velocity potential of the incident wave is expanded to obtain the incident wave expansion coefficient. The relationship between the incident wave expansion coefficient and the scattered wave expansion coefficient is established by the Q matrix method to obtain the scattered wave expansion coefficient. The far-field scattering morphology function and target intensity are calculated based on the scattered wave expansion coefficient, and a target scattering characteristic model for a spherical target is constructed. For a finite-length cylindrical target, the total scattered field is decomposed into side scattering and end scattering. The side scattering function and end scattering function are modeled and solved to obtain the side scattering function and end scattering function respectively. The total scattering function is obtained by superimposing them, and a target scattering characteristic model of the target intensity changing with frequency and observation angle is generated.

[0009] Preferably, for side scattering, the differential unit of the finite-length cylindrical target is equivalent to the differential unit of the infinite-length cylinder of the same radius. The scattering coefficient is determined according to the Bessel function, Hankel function and boundary conditions, and then substituted into the scattering wave function to obtain the side scattering function. For end-face scattering, based on the modified Kirchhoff integral, the reflection coefficient of each unit is equivalent to the reflection coefficient of an infinite plane. The scattered wave in the shadow region of the scatterer is set to zero. The end-face scattering function is obtained by combining the density ratio and the sound speed ratio.

[0010] Preferably, the process of constructing the interface scattering model includes: Define the scattering intensity formula and the geometric characteristics and acoustic parameters of the scattered wave and the incident wave vector. Based on the geometric characteristics and acoustic parameters of the scattered wave and the incident wave vector, calculate the component differences between the scattered wave and the incident wave vector in the horizontal and vertical directions. A two-dimensional roughness spectrum with two parameters is used to characterize the interface roughness, and an incoherent scattering cross section containing the physical characteristics of the interface is constructed using the small slope approximation method. For the seabed and sea surface, the incoherent scattering cross sections adapted to the interface roughness and physical characteristics are calculated respectively. Substituting them into the scattering intensity formula, the interface scattering intensity is output, and the interface scattering model is completed.

[0011] Preferably, the formula for calculating the scattering intensity of the bubble cloud is: ; In the formula, For acoustic wavenumber, Let be the vertical wavenumber of the incident sound field. Let be the vertical wavenumber of the scattered sound field. This represents the depth of friction due to air friction.

[0012] Preferably, the process of constructing a unit scattering model includes: Based on the bistatic coordinate system and the seabed and sea surface, an equal time delay surface is constructed, and several scattering units are obtained by dividing the space according to the radial step size and the azimuth step size. Based on the horizontal distance, area, time delay, incident grazing angle, and scattering grazing angle of each scattering unit, the scattering term, propagation term, and contribution to reverberation of each scattering unit are calculated, and the contributions are superimposed to obtain the reverberation time series.

[0013] Preferably, the formula for obtaining the reverberation time series is: ; In the formula, For reverberation time series, x-axis coordinate For time, To give every contribution Introduced random phase, The number of scattering rings. The number of scattering units. For the first The scattering ring of the th scattering ring The time delay of the scattered echo corresponding to each scattering unit.

[0014] Preferably, the process of constructing a three-dimensional dynamic sea surface includes: determining the amplitude and angular frequency of the cosine wave based on the JONSWAP spectrum, determining the direction angle of the cosine wave based on the SWAP direction spectrum, and superimposing the amplitude, angular frequency and direction angle of the cosine wave to obtain a three-dimensional dynamic sea surface.

[0015] The beneficial effects of this application are as follows: This invention provides a method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment. First, a three-dimensional dynamic sea surface is constructed using the JONSWAP spectrum and SWAP direction spectrum. Combining the interface scattering model and the sea surface bubble model, the reverberation of the sea surface, seabed, and sea surface bubbles is comprehensively considered, and the sea surface scatterers are divided into units to obtain the reverberation time series. A marine noise model is constructed by combining five main types of marine environmental noise: turbulent pressure fluctuation noise, shipping noise, wind noise, rain noise, and thermal noise, to deeply analyze the comprehensive impact of complex marine environments on sonar detection performance. Then, a target scattering characteristic model is constructed based on acoustic scattering theory to analyze the scattering characteristics of typical targets such as spheres and cylinders, and to quantitatively evaluate the sonar's detection capability, tracking accuracy, and anti-interference performance. Finally, a channel structure is constructed using the BELLHOP ray acoustic model, and a path management algorithm is used to correct the time-varying channel. The acoustic ray data output by the BELLHOP ray acoustic model is transformed into a matrix with constant dimension and traceable path, yielding the direct wave signal and the target echo signal. Finally, the direct wave signal, target echo signal, reverberation time series, and ocean noise model are superimposed to obtain the received signal of the bistatic sonar target detection system receiving station, thus completing the construction of the simulation platform and avoiding the problems of sea field tests being easily affected by weather and sea conditions, high cost, long cycle, and high safety risks. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of the overall process for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment, provided in an embodiment of this application; Figure 2 A flowchart of a reverberation simulation module provided in one embodiment of this application; Figure 3 A schematic diagram of a scattering signal provided in an embodiment of this application; Figure 4 A schematic diagram illustrating the isochronous arrival of interface scattering signals onto an ellipse, as provided in an embodiment of this application. Figure 5 This is a schematic diagram of the distribution structure of a unit scattering model provided in an embodiment of this application; Figure 6 This is a side view of the element division principle of an element scattering model provided in an embodiment of this application; Figure 7A three-dimensional diagram illustrating the element division principle of an element scattering model provided in an embodiment of this application; Figure 8 A schematic diagram illustrating the interrelationship of three underwater acoustic channels provided in an embodiment of this application; Figure 9 A schematic diagram illustrating the construction of an underwater acoustic channel according to an embodiment of this application; Figure 10 A visualization of target detection using a bistatic sonar system provided in an embodiment of this application. Detailed Implementation

[0018] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0019] Please see Figure 1 This application provides a method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment, comprising: S1: Construct a three-dimensional dynamic sea surface based on the JONSWAP spectrum and SWAP direction spectrum.

[0020] The amplitude and angular frequency of the cosine wave are determined based on the JONSWAP spectrum, and the direction angle of the cosine wave is determined based on the SWAP direction spectrum. The amplitude, angular frequency and direction angle of the cosine wave are superimposed to obtain the three-dimensional dynamic sea surface.

[0021] Specifically, constructing a three-dimensional dynamic sea surface refers to describing the instantaneous state of the ocean surface using data and physical methods. The complex random sea surface is viewed as a linear superposition of numerous simple cosine waves with different amplitudes, angular frequencies, and azimuth angles. The JONSWAP spectrum is used to define the basic parameters of the waves, such as energy and frequency; the SWAP directional spectrum is used to describe the energy distribution of the waves at different frequencies and propagation directions. Finally, the WAFO toolbox is used to perform statistical analysis and simulation of random waves and random loads to construct the three-dimensional dynamic sea surface.

[0022] The calculation of wave parameters under different wind speed levels using the JONSWAP spectrum was used to set a reasonable amplitude for the cosine wave. angular frequency Initial values ​​are constant. The formulas for the wave power spectrum and the wave spectrum expressed in terms of angular frequency are: ; In the formula, For the soundtrack of the ocean waves, Angular velocity, a dimensionless constant ,in, The length of the wind zone For wind speed, spectral peak frequency , The peak enhancement factor is 3.3, with an average value of 3.3. For peak shape parameters, when < hour, =0.07, when > hour, =0.09.

[0023] The JONSWAP wave spectrum describes the one-dimensional relationship between sea surface energy and frequency. This application uses the SWAP directional spectrum provided by the Wave Stereoscopic Observation Project to describe the direction function of wave frequency propagation relative to wind direction. The SWAP directional spectrum, based on measurement data from the Wave Stereoscopic Observation Project, describes the energy distribution of waves at different frequencies and in different propagation directions. The directional angle... The formula used to describe the direction of wave propagation is as follows: ; In the formula, For directional spectrum, , , and The coefficient controlling the shape of the energy distribution direction determines the concentration and form of wave energy in different directions. ω is the angular velocity.

[0024] By combining the JONSWAP spectrum and the SWAP direction spectrum, we obtain The formula is as follows: ; In the formula, The wave direction spectrum is used to describe the wave energy as it varies with the angular frequency. and direction of dissemination θ Distribution of The frequency spectrum of the sea surface. This is the SWAP directional spectrum.

[0025] A three-dimensional dynamic sea surface is described by superimposing multiple cosine waves to depict the trajectory of points on the ocean surface. These cosine waves include different amplitudes, wavelengths, initial phases, and directions, enabling the simulation of the diversity and complexity of ocean waves. The formula is as follows: ; In the formula, The instantaneous height of the waves. For amplitude, Angular frequency, For time, It is the acceleration due to gravity. It is the direction angle. For the initial phase, The superposition number of cosine waves. Horizontal direction x Axis coordinates.

[0026] S2: Construct an interface scattering model based on the small slope approximation method to calculate the interface scattering intensity; construct a sea surface bubble model to calculate the bubble cloud scattering intensity; combine the interface scattering intensity and the bubble cloud scattering intensity to construct a unit scattering model, divide the scatterers on the seabed and sea surface into units, and obtain the reverberation time series.

[0027] Please see Figure 2 The interface scattering model, the sea surface bubble model, and the unit scattering model constitute the reverberation simulation model, which is used to convert environmental information and source signals into reverberation time series.

[0028] Specifically, an interface scattering model is first constructed, including a seabed scattering model and a sea surface scattering model. This application calculates the scattering intensity by constructing the interface scattering model. Specific steps include: Define scattering intensity. ,in, The scattering cross-section per unit area is a dimensionless quantity. In this application, the scattering intensity is the average far-field (plane wave) quantity.

[0029] In one alternative embodiment, please refer to Figure 3 This is a schematic diagram illustrating the principle of seabed scattering signals. Figure 3 The principle diagram of the sea surface scattering signal is obtained by inverse mapping along the Z-axis, corresponding to the direction of increasing depth. In the diagram, and These represent the incident wave vector and the scattered wave vector, respectively. and Angle with the xoy plane (seabed plane) , These are the incident grazing angle and the scattered grazing angle, respectively. The bistatic angle is the angle between the incident direction and the scattering direction. Where 0 < ≤90°、0< ≤180°, -180°< ≤180°. When the bibase is split at an angle... When the angle is 180°, it corresponds to backscattering; when the bistatic angle is... When the angle is 0°, it corresponds to specular reflection.

[0030] The scattering intensity model satisfies reciprocity, that is... From the perspective of angle, the incident wave vector and scattered wave vector It can be represented as: ; ; In the formula, , which is the acoustic wavenumber. For sound wave frequency, c 0 represents the speed of sound in bubble-free seawater at the interface. , , These are unit vectors in a three-dimensional Cartesian coordinate system, representing the horizontal direction, lateral horizontal direction, and vertical / normal direction of the incident surface, respectively.

[0031] The expression for the interface scattering cross section depends on the incident wave vector. and scattered wave vector The magnitude of the difference in the horizontal and vertical directions Its magnitude is expressed in terms of the scattering angle as: ; ; In the formula, Let be the magnitude of the difference between the incident wave vector and the scattered wave vector in the horizontal direction. This is the vertical component of the difference between the incident wave vector and the scattered wave vector.

[0032] This application employs Voronovich's small-slope method to predict the contribution of the boundary interface to the total scattering. The lowest-order small-slope approximation (SSA) model can simulate the interface scattering intensity at all orders of surface height h, as well as the first-order scattering intensity of the derivative of height h (surface slope). Using the local small-slope approximation instead of the standard first-order perturbation approximation improves the accuracy of the prediction.

[0033] Bottom and surface roughness are treated as Gaussian random processes, each described by a two-parameter, isotropic two-dimensional roughness spectral density, in the form of: ; In the formula, For two-dimensional roughness spectral density, ∈(2,4), where is the boundary roughness spectral index. The larger the value, the stronger the frequency dependence. The standardized reference distance is 1 meter. The power spectrum intensity parameter represents the seabed topographic undulations (roughness).

[0034] The lowest-order small slope of the incoherent scattering cross section of a random rough interface is approximated as: ; In the formula, For a random, rough interface, the incoherent scattering cross section represents the ratio of scattered energy to incident energy per unit area and unit solid angle; it is a dimensionless quantity. It is an algebraic form that depends on the boundary conditions at the interface. For the integral involving the roughness space spectroscopy. when v ≡( -2) / 2, that is v When ∈(0,1), the integral of the roughness space spectrum is: ; ; In the formula, For an integral term involving the roughness space spectrum, Let be the middle term of the integrand. It is a zeroth-order Bessel function of the first kind. For integration variables, The value is given by the following formula: ; In the formula, This is a dimensionless parameter that combines statistical parameters of surface roughness. Among them, the root mean square roughness coefficient... Defined as: ; If the speed of sound is independent of frequency. The only frequency dependence of the parameter ,at this time and The relationship is: It is evident that the only environmental parameter affecting frequency dependence is the boundary roughness spectral index. If the speed of sound depends on frequency, then , as well as All of these will produce complex frequency dependencies.

[0035] Constructing a seabed scattering model requires environmental parameters: the ratio of solid mass density to fluid mass density. Complex sound velocity of P-waves in solids (including compressional wave velocity and attenuation) Complex sound velocity of S-waves in solids (including shear wave velocity and attenuation) , respectively corresponding to and The complex wave number is: ; ; In the formula, The complex acoustic wavenumber of longitudinal waves in the solid medium of the seabed. denoted as the complex acoustic wavenumber of transverse waves in the solid medium of the seabed.

[0036] Define three pairs of general functions , , Used for construction The formula is as follows: ; ; ; In the formula, For the glancing angle, For the vertical wavenumber component of the P-wave, For the vertical wavenumber component of the transverse wave, , and For use in building The intermediate variable defined, subscript j This indicates its angle dependence. Among them, and The formula is as follows: ; ; ; In the calculation, the incident angle and the glancing angle are respectively... and scattering glancing angle Substitution We get the following formula: ; In the formula, The incident wave vector The projection component on the horizontal plane, Scattered wave vector Projected components on the horizontal plane.

[0037] In summary, we can obtain The expression is: ; In the formula, As an algebraic form, it reflects the influence of the physical properties of the interface (such as whether it is a fluid-fluid interface or a fluid-elastic solid interface) on sound wave scattering. , and for , and exist j =1 (i.e.) θ j = θinc The value at that time, , and for , and exist j =2 (i.e.) θ j = θ scat The value when ).

[0038] In summary, for the seabed scattering model, the seabed scattering intensity It depends on eight environmental parameters, namely the speed of sound. And 7 geophysical parameters: 、 , , , , and .

[0039] Construct a sea surface scattering model and provide sea surface scattering data. Formula for calculating the value: ; The sea surface exhibits roughness at various scales, which can be represented using an isotropic spectral model. Its power spectral intensity parameters are given by the following equation: ; In the formula, The wind speed at a height of 10 meters (unit: m / s). In this context, for a given wind speed, there are two free fitting parameters. and :in The frequency-dependent characteristics that determine the spectrum, and and These parameters collectively determine the energy level intensity. In open sea areas, the range of values ​​for these parameters is as follows: , .

[0040] Therefore, in the sea surface scattering model, the sea surface scattering intensity The value depends on four environmental parameters: (Reference speed of sound) (Wind speed) (Spectral amplitude coefficient) and (Spectral index parameters). It is particularly important to note the sea surface scattering intensity in the sea surface scattering model. Frequency dependence only through its frequency dependence The relationship is reflected, while its bibasic angle dependency is only through | | The functional relationship of the parameters.

[0041] Next, a sea surface bubble model is constructed, incorporating the scattering effect of broken bubbles generated by sea surface waves on sound waves into the model. The scattering intensity of the bubble cloud is then calculated. The formula is as follows: ; In the formula, For acoustic wavenumber, Let the vertical wavenumber of the incident sound field be defined as follows: , The vertical wavenumber of the scattered sound field is defined as follows: , The reduced depth of air friction is calculated based on existing empirical formulas for the scattering intensity of wind-induced bubble layers at the sea surface. With wind speed The following relationship exists between them: ; Scattering intensity of bubble cloud Scattering intensity from sea surface By integrating the results, we obtain the bistatic surface scattering strength (SSS) model, as shown in the following formula: ; In the formula, The scattering intensity of the bubble cloud, The intensity of scattering from the sea surface.

[0042] Finally, a unit scattering model is established, discretizing the sea surface and seabed into a large number of scattering units with similar scattering characteristics. Each scattering unit includes several scatterers. This application uses the scattering characteristics of all scatterers within a scattering unit as the scattering characteristic of that unit. Compared to the traditional point scattering model, the unit scattering model reduces computational complexity while maintaining simulation accuracy. The echo intensity of a scattering unit is determined by its scattering intensity and the round-trip propagation loss of the sound wave along the propagation path. Based on this, the amplitude of the echo signal generated by each scattering unit at the receiver is obtained. All unit echo signals, including amplitude, time delay, and random phase, are summed on the time axis to synthesize a reverberation time series. This series effectively simulates the reverberation process in a real marine environment in terms of statistical characteristics such as energy attenuation, power spectrum, and amplitude distribution.

[0043] Specifically, please refer to Figure 4 In this application, the receiver is located directly below the transmitter. A coordinate system for the bistatic system is established, with the sea surface interface defined. =0, the positions of the transmitter and receiver are respectively (0,0, )and (0,0, ), the seabed interface is = flat, The depth is the sea surface. For a bistatic configuration, the point where the sum of the distances to the transmitter and receiver is located forms an ellipsoid, with the transmitter and receiver being the two foci of this ellipsoid. This ellipsoid is called the isochronous delay surface of the bistatic sonar. When the ellipsoid is large enough, it intersects the seabed and the sea surface with circles respectively, and the scattered signals from the scatterers on these circles will arrive at the receiver at the same time.

[0044] Taking the moment the signal is emitted from the transmitter as time zero, consider the time delay of the scattered signal from a large number of scatterers. When the time arrives at the receiving end, the corresponding ellipsoid equation is: ; In the formula, The distance from the scattering point to the emitter. The distance from the scattering point to the receiver. For the speed of sound, It is the time delay of the entire process from the emission of sound waves at the transmitter, through scattering by the scatterer, to their reception at the receiver.

[0045] Since the transmitter and receiver are located on the same vertical line, the ellipsoid intersects the seabed or sea surface interface in a circle, with the center of the circle being the projection of the transmitter and receiver onto the seabed or sea surface interface. Therefore, the scattered signals received by the receiver at different times will correspond to concentric rings distributed on the seabed or sea surface interface. The scattered signals from the scatterers on different rings will arrive at the receiver at different times, with the scattered signals from the scatterers on the rings with larger radii experiencing greater time delays.

[0046] Figure 5 This is a schematic diagram of the distribution of a unit scattering model, showing the scatterers from the seabed and sea surface arranged in concentric rings (width is...). The process of dividing scattering units into different scattering units. When When the scattering angle is sufficiently small, the incident grazing angle and the scattered grazing angle of the scatterer within the same ring are the same, and the scattering intensity is equal, so the contribution to reverberation can be calculated uniformly. Compared with the point scattering model, which calculates each scatterer individually, this method significantly reduces the computational load and improves computational efficiency.

[0047] Figure 6 , Figure 7 The images show a side view and a 3D view of the unit scattering model applied to the seabed. Within the range of the reverberant seabed pitch angle, according to... Divide into steps. Scattering ring, the first The time delay for the scattered signal from each scattering ring to reach the receiver is given by the following formula: ; In the formula, For the first The time delay for the scattered signal from each scattering ring to reach the receiver. The speed at which sound waves travel in water. For sea depth, and These are the depths of the transmitting and receiving ends, respectively. For the first A scattering ring The distance from the axial center to the center of the annulus is given by the following formula: ; Once the scattering rings are divided, each scattering ring is arranged according to the azimuth direction. Divide the step size into (positive integer) scattering units, It can be represented as: ; In the formula, This refers to the intersection of the directional properties of the transmitting and receiving transducers in the azimuth angle. , These are the starting and ending values ​​of the azimuth directional range, respectively. If both the transmitting and receiving transducers are isotropic, then it is not necessary to perform secondary division of the scattering ring at the azimuth angle.

[0048] Based on the above division of scattering units, the reverberation areas of the seabed and sea surface are divided into a total of [number missing]. There are scattering units. The intermediate variables needed to calculate the reverberation time series include: the horizontal distance from the center of each scattering unit to the transmitter or receiver. Area of ​​each scattering unit The time delay corresponding to each scattering unit The distance from the transmitted signal to the center of each scattering unit The distance from the scattered echo to the receiver The incident grazing angle corresponding to each scattering unit and scattering glancing angle ; Scattering terms corresponding to each scattering unit Dissemination items The contribution of each scattering unit to the reverberation The process of calculating intermediate variables includes: For underwater reverberation, the first The scattering ring of the th scattering ring Area of ​​each scattering unit It can be represented as: ; For the first The scattering ring of the th scattering ring The time delay of the scattered echo corresponding to each scattering unit is expressed as: ; No. The scattering ring of the th scattering ring Each scattering unit corresponds to an incident grazing angle. and scattering glancing angle It can be represented as: ; ; Scattering term of seabed reverberation Represented as: ; In the formula, It is an incoherent scattering cross section of a random rough interface.

[0049] Dissemination Items It is related to the sound absorption of seawater and the attenuation of sound signal propagation, and can be expressed as: ; In the formula, For the speed of sound, The time delay is the time it takes for a sound wave to travel from the transmitter, through the scatterer, and be received by the receiver. The sound absorption coefficient of seawater.

[0050] So, the total contribution of each scattering unit to the reverberation With scattering term Dissemination items and the number of scatterers in each scattering unit The relevant formula is: ; ; In the formula, =1,2,…, , =1,2,…, The number of scatterers in each scattering unit follows a Poisson distribution, and Density represents the number of scatterers per unit area. For the first The scattering ring of the th scattering ring The area of ​​each scattering unit, For the first The scattering ring of the th scattering ring The number of scatterers in each scattering unit. For the first The scattering ring of the th scattering ring In each scattering unit, the total contribution of each scattering unit to the reverberation is... For the first The scattering ring of the th scattering ring Scattering terms of each scattering unit, For the first The scattering ring of the th scattering ring The propagation term of each scattering unit.

[0051] Ultimately, the reverberation time series of both the seabed and the sea surface were synthesized by coherently superimposing the contributions of each scatterer within all scattering units, as shown in the following formula: ; In the formula, x-axis coordinate For time, To introduce a random phase for each contribution (in The random phase, which is uniformly distributed within the interval, reflects the random interference characteristics when the echoes of a large number of sub-scatterers are superimposed, so that the simulated reverberation signal can approximate the actual observed reverberation process in terms of statistical characteristics.

[0052] S3: Combine turbulent pressure fluctuation noise, shipping noise, wind noise, rain noise, and thermal noise to obtain an ocean noise model that conforms to the WENZ spectrum.

[0053] The environmental noise model calculates the total noise by superimposing the contributions of five effects, namely turbulent pressure fluctuation noise. Shipping noise Wind-induced noise Rain noise and thermal noise .

[0054] Turbulent pressure fluctuation noise The nonlinear interaction effect between wind-generated sea surface waves is characterized using empirical formulas. Within the 1–100 Hz frequency band, turbulent pressure fluctuations dominate the noise spectrum, depending solely on frequency. The power-law function. This function exhibits a linear relationship in log-frequency space, with a slope of... The intercept is The formula is: ; Among them, parameters and intercept The frequency of this phenomenon is not constant in different areas of the ocean and depends on factors such as water depth, ship noise, and wind speed.

[0055] Shipping noise Depends on frequency Ship density (low, medium, or high) and water depth (deep or shallow water). This item is an approximation of the curves for low, medium, and high ship densities, and the formula is: ; in, Depending on the water depth, when 30 represents deep water; when 65 indicates shallow water. Depending on the shipping density level, when When it is 1, it represents low shipping density; when When the value is 4, it represents medium shipping density; when When the value is 7, it indicates high shipping density.

[0056] Wind noise Originating from multiple factors, including breaking waves from bubbles, water droplets, and surface waves, and depending on frequency. Wind speed at a height of 10 meters U And water depth (shallow or deep). Wind noise. (Unit: dB) can be summarized as follows: ; Rain noise Depends solely on sound wave frequency Its expression is: ; In the formula, the parameters 、 、 、 Depends on rainfall rate (in mm / h).

[0057] Thermal noise level That is, noise caused by the excitation of water molecules depends only on frequency. Its expression is: ; In the formula, Thermal noise level, The frequency of the sound wave.

[0058] S4: Based on acoustic scattering theory, construct a target scattering characteristic model.

[0059] For spherical targets, the Q-matrix method is used for numerical solution based on mature acoustic scattering theory. The simulation process includes defining the geometric dimensions, material density, longitudinal wave velocity, and transverse wave velocity of the spherical target, and setting the acoustic parameters of the surrounding water medium. After determining the frequency range and incident angle of the incident plane wave, the Q-matrix method is used to solve for the key coefficients describing the characteristics of the scattered sound field, thereby calculating the far-field scattering pattern function and target strength (TS) of the target. This generates an accurate spectrum of target strength as a function of frequency and observation angle, providing reliable reference data.

[0060] In a liquid, sound pressure satisfies the wave equation as follows: ; In the formula, For the Laplace operator, For wave number, = / , Angular frequency, The speed of sound in water. This is the scattered sound pressure.

[0061] According to Green's function theory, a scattered wave at a point in space can be expressed as a function of the scattered wave and its gradient at the surface of the scattering body, that is: ; In the formula, It is a scattered wave. Relative to surface coordinates gradient operator, For the position on the surface of the scatterer The scattered sound pressure value at that location, For free space Green's function, For wave number, i and s All are subscripts, among which, i Indicates incident radiation. s Indicates scattering, , r ' represents the coordinates of a point on the surface of the scatterer. It is the position vector of a point in space.

[0062] According to Kirchhoff's integral theory, considering the far field, the above equation can be simplified to: ; In the formula, Let be the unit normal vector of the scatterer surface pointing outward.

[0063] According to the theory of radiated sound fields, its scattering waveform function is: ; Therefore, its scattering wave function is: ; As shown in the above equation, the scattering waveform function at a point in space can be obtained by solving for the scattered sound pressure on the scattering surface. That is, once the value of the scattered sound pressure on the surface of the scattering body is given, the scattered wave at any point in space can be expressed as a function of the scattered wave and its gradient on the surface of the scattering body.

[0064] For the boundary value problem outside the underwater spherical target, its Helmholtz equation is: . Let be the total velocity potential, and be the sum of the incident wave velocity potential and the scattered wave velocity potential, where Let the wave number be the incident sound wave. Let the incident wave velocity potential be... The potential for the scattered wave velocity is... The vibration velocity and sound pressure of the sound wave at that location are respectively: ; ; In the formula, Let r be the vibration velocity of the sound wave at point r. Let r be the sound pressure level of the sound wave at point r. For the total velocity potential , In space r The sound pressure at that location, r It is a spatial position vector or radial distance. The density of seawater, Let f(x) be the basis functions, and f(x) be the solutions to the scalar Helmholtz equations in spherical coordinates. These are the expansion coefficients, corresponding to the weight coefficients of each basis function.

[0065] ; ; In the formula, For associated Legendre functions, This represents the order or azimuth mode number of the spherical harmonic function. The azimuth angle in spherical coordinates. or The characteristics of the basis functions as a function of azimuth angle are described. Let the wave number be the incident sound wave. For Hankel functions of the first kind, , is the Newman constant, which is 1 when n=0 and 2 when n=1 or 2.

[0066] Expanding the incident plane wave according to the basis functions, its velocity potential is expressed as: ; In the formula, Let the incident wave velocity potential be... Let be the expansion coefficient of the incident wave. As basis functions, Represents the basis functions Take the real part.

[0067] The relationship between the incident wave expansion coefficient and the scattered wave expansion coefficient is as follows: ; In the formula, The scattering wave expansion coefficient is... Let be the incident wave expansion coefficient. The transfer matrix is ​​defined as follows: ; ; In the formula, Let Q be the matrix. For an element in the Q matrix, , , For Kronek Symbols, when two subscripts are equal (e.g.) Its value is 1 if it is not 1, otherwise it is 0. Let the wave number be the incident sound wave. , These are the polar angle and azimuth angle in spherical coordinates, respectively. The radial distance from the surface of the scatterer is denoted by . Radial distance r opposite angle The partial derivatives, , For spherical wave basis functions.

[0068] When a plane wave is incident on a small sphere, the plane wave can be decomposed into a superposition of spherical waves, i.e. ; In the formula, Let be the spatiotemporal distribution function of the incident sound pressure. The imaginary unit, For time variables, To find the order of the summation series, The sound pressure level is the amplitude. ω is the angular frequency.

[0069] Because at this time the calculation and Regardless, simplifying the basis functions, we get: ; In the formula, For simplified basis functions, For wave number, Radial distance, For order, For Legendre polynomials, is the polar angle in spherical coordinates.

[0070] Using the basis functions, velocity potential, and parallel wave, the plane wave expansion coefficients can be obtained as follows: ; ; In the formula, For plane wave expansion coefficients, The elements of the Q matrix, For Kronek symbol, Let the wave number be the incident sound wave. , These are basis functions.

[0071] For the ball: , We can obtain: ; Considering the hard boundary conditions, the plane wave expansion coefficients are positive. Substituting the basis functions into the above equation, we obtain the Q-matrix expression characterizing the scattering properties of an underwater spherical target in the non-incident direction: ; In the formula, The symbol for Kronecker. For wave number, Let be the radius of the small ball. =cos θ As an intermediate variable, , For Legendre polynomials, For a sphere of the first kind, the Bessel function is... The derivative of the Hankel function of the first kind of sphere. θ is the angle between the direction of sound wave reception and the direction of incident.

[0072] As can be seen from the above equation, for a spherical target, the values ​​of the Q matrix elements are related to the incident wave frequency and the radius of the sphere. Therefore, the target scattering characteristic model has the following properties: The Q matrix contains information about the shape of the scattering target. For different scatterers, when solving for scattering characteristics, only the geometric equations describing their shape need to be changed. The expression is therefore generalizable; The size of the Q matrix elements is related to the frequency. As the frequency changes, the value of the Q matrix elements changes. By solving the Q matrix, the variation of the scattered sound field of an underwater spherical target with frequency can be obtained. Based on the Q matrix, the T matrix is ​​derived, and the expression for the target scattered sound pressure is obtained. Therefore, this method has certain advantages in solving the scattering characteristics of underwater targets in non-incident directions.

[0073] For finite-length cylinders, this application employs a more refined scattering simulation model to ensure the accuracy of the analysis. The core idea is to decompose the total scattered field of the finite-length cylinder into a coherent superposition of scattering from the cylinder's sides and end faces, effectively accounting for the complex diffraction phenomena caused by discontinuities in the target's geometry (i.e., edge effects). In the simulation, the cylinder's length, radius, material properties, and the spatial positions of the sound source and receiver need to be set. By modeling and solving the side and end face scattering separately, and then coherently combining the two contributions, the total scattered sound pressure at any receiving point can be obtained. This method can accurately predict the target intensity (TS) characteristics of a finite-length cylinder at different frequencies and different incident and receiving angles (including bistatic configurations), thus providing high-fidelity simulation data support for this application when dealing with complex targets.

[0074] For side scattering, assuming that the acoustic scattering of a differential element of a finite-length cylinder is equivalent to that of a differential element of an infinite-length cylinder of the same radius, the internal field of its near-field scattering is consistent with that of the infinite-length cylinder. Therefore, the far-field scattering function can be calculated based on Green's function theory. Consider an incident plane wave located in the xz plane, with the axis of the cylinder taken as the z-axis. In a finite cylindrical coordinate system, the incident wave is written as: ; In the formula, Let be the expression for the sound pressure field of the incident sound wave. The spatial phase factor of the incident plane sound wave. Let be the angle between the incident plane and the plane perpendicular to the axis of the cylinder. It is the azimuth angle. It is a Bessel function of the first kind, nth order. For Neumann factors, if =0, =1; otherwise The value is 2.

[0075] The internal field can be solved as follows: ; In the formula, Internal sound pressure. For axial phase factor, For expansion coefficients, Radial coordinates, The wave number is the number of the cylinder's interior.

[0076] The scattered wave can be written as: ; In the formula, For scattered sound pressure, The scattering coefficient is... This is a Hankel function of the first kind.

[0077] Scattering coefficient As determined by the boundary conditions, the radial components of pressure and particle velocity must be continuous at the boundary. This gives us the following equation: ; In the formula, The nth power of the imaginary unit For wave number, Where is the radius of the cylinder. It is the derivative of the first kind of nth-order Bessel function.

[0078] in, The coefficient is determined by the physical properties of the cylinder and its surrounding medium, and its formula is: ; In the formula, , These represent the mass and density inside and outside the cylinder, respectively. Where is the radius of the cylinder. , , The wave number inside the cylinder. The wavenumber of the medium outside the cylinder. The derivative of the first kind of nth-order Bessel function, Let denote the derivative of the first-order n-th order Hankel function.

[0079] Under the assumption that a finite-length cylindrical differential element is equivalent to an infinite-length cylindrical infinitesimal element of the same radius, substituting the scattering coefficient into the scattering wave function yields the side scattering function of the finite-length cylinder. Let the incident and scattering directions be represented by spherical coordinates, and points on the cylinder surface by cylindrical coordinates. The incident direction can then be obtained as follows: The scattering direction is . and These are the incident and scattered wave vectors, respectively, with magnitudes of... We can conclude that: ; In the formula, Let be the scattering function. The imaginary unit, For the length of a finite-length cylinder, for, The scattering coefficient is... The modal order is... The azimuth angle is the scattering angle.

[0080] in, ; In the formula, A shape factor used to describe the diffraction effect or orientation pattern described due to the finite length of the cylinder. The scattering angle is... The angle of incidence is denoted as .

[0081] ; For comparison, the results of the Stanton number cylinder method are presented below: ; In the formula, Let be the scattering function of the Stanton cylinder method. Based on the Lonski determinant, we obtain the following equation: ; In the formula, For the first kind of nth order Bessel function, The derivative of the first-order n-th order Hankel function, The derivative of the first-order nth-order Bessel function. For the first kind of n-order Hankel function, This is a general variable for the functions above and below.

[0082] Therefore, when or At that time, the cylinder method and The results are the same.

[0083] Consider the end-face effect for a finite-length cylinder. This effect is negligible when the incident and scattered waves are nearly perpendicular to the axis, or when the scattering body is a slender, deformed cylinder with small circular end faces. The end faces are flat surfaces, and their scattering can be obtained through a modified Kirchhoff integral. This integral assumes that the scattered wave is the superposition of scattering from each surface element, and that the reflection coefficient of each element is equivalent to the reflection coefficient of an infinite plane. It also stipulates that the scattered wave in the shadow region of the scattering body is zero. Based on this, the scattering function can be derived: ; In the formula, The end-face scattering function, Density ratio, The sound velocity ratio or wavenumber ratio parameter. for, For phase factor, The outward normal unit vector of the surface. The scattering direction, Let be the surface coordinate vector. It can be integrated as: ; In the formula, The end-face scattering function, For the effective wavenumber component, It is a first-order Bessel function of the first kind.

[0084] in, ; ; The complete scattering function of a finite-length cylinder is given by and The sum of the two results is given. Define the target intensity function: ; In the formula, For target strength, This is the total scattering function.

[0085] S5: Based on the BELLHOP ray acoustic model, a channel structure is constructed, and a path management method is used to correct the time-varying channel to obtain the direct wave signal and the target echo signal, thereby achieving continuous tracking and stable output of channel parameters.

[0086] Please see Figure 8 Based on the Bellhop ray acoustic model, simulations were performed on three underwater acoustic channels involved in the bistatic sonar model: direct wave channel H1 (transmitter-receiver), target echo channel H2 (transmitter-target), and target echo channel H3 (target-receiver). The transmitted signal passes through the direct wave channel H1 to obtain the direct wave signal signal_SR. The transmitted signal passes through the target echo channel H2 to obtain the target incident signal, which is then processed by the target scattering characteristic model to obtain the scattered signal. The scattered signal passes through the target echo channel H3 to obtain the target echo signal.

[0087] Please see Figure 9 Taking the direct wave channel H1 (transmitter-receiver) as an example, the channel structure information (.env file) is first compiled based on environmental information such as the location of the transmitter and receiver, water depth, and sound velocity profile. Then, based on the constructed three-dimensional dynamic sea surface, the sea surface waveform file (.ati file) needed for the Bellhop acoustic model is compiled, and the seabed topography is customized and compiled into a seabed topography file (.bty). Bellhop obtains detailed information about the channel and the transmitted signal from a physical perspective by reading these three files, thereby obtaining the channel's impulse response. During this process, the path management algorithm continuously and stably tracks the changes in the sound path caused by drastic environmental changes.

[0088] Specifically, during the propagation of sound waves in the ocean, the energy attenuation mainly comes from spreading loss, absorption loss, and reflection loss. The spreading loss is obtained from the following formula: ; In the formula, To extend the loss, For expansion coefficient, For the distance of propagation.

[0089] When sound waves propagate at close range in the form of spherical waves, the spread loss is: When sound waves propagate over long distances in the form of cylindrical waves, the spread loss is: .

[0090] The absorption loss is calculated using Thorp's empirical formula, as follows: ; In the formula, The sound absorption coefficient (dB / km) is expressed as the number of decibels lost by the absorption effect per kilometer of propagation. The frequency of the sound wave is kHz.

[0091] The sea surface reflection loss is expressed by the following formula: ; In the formula, The loss due to sea surface reflection (dB) and These are the reflected and incident sound pressure amplitudes, respectively. Loss due to reflection from the sea surface.

[0092] The seabed reflection loss is expressed by the following formula: ; In the formula, The loss due to seabed reflection (dB) This represents the seabed reflection coefficient.

[0093] Therefore, the multipath self-interference path losses obtained based on the spread loss, absorption loss, and reflection loss are as follows. It can be expressed by the following formula: ; In the formula, Let n be the propagation distance of the nth root path. The number of times the nth path experiences seabed reflections. For the first The number of times the root path undergoes sea surface reflections.

[0094] By subtracting the path loss from the emitted sound source level. The gain of each path can be obtained as follows Combining multipath to achieve time delay The multipath self-interference channel can be described as: ; The changes in the propagation path of multipath interference caused by sea surface fluctuations will alter the arrival delay, spread loss, and absorption loss of each path. Sea surface waveform data at different times is generated using the WAFO toolbox, and time-varying paths are tracked using path tracking management methods.

[0095] The path management algorithm is a multipath channel path management algorithm based on the classification of sound ray physical characteristics. It abandons the fragile indexing mechanism of traditional methods that rely solely on delay sorting, and instead classifies sound rays according to the physical laws of sound propagation. It utilizes the number of sea surface reflections of sound rays. and number of reflections from the seabed To determine the physical type of the voice.

[0096] Create a vocal ray dictionary, with each column defining a combination of reflection counts. For each input vocal ray i, its reflection count is used to look up the corresponding vocal ray type in the vocal ray dictionary. This is to ensure the output matrix... With a constant dimension, the algorithm pre-allocates a fixed total number of columns. Total number of columns Determined by the number of vocal timbre types and the maximum capacity of each type: Output matrix Logically divided into A contiguous block of memory, each with a capacity of [number] blocks. A certain type of voice is stored and searched only within the corresponding index type range.

[0097] The implementation of the path management algorithm is divided into two stages: the initial generation selection (initialization) and the subsequent generation selection (tracking, matching and virtualization), which is controlled by whether the input parameter (delay dictionary) is empty.

[0098] In the first iteration, when the input parameters are true, an initialization operation is performed. All input sound rays are traversed to find the sound ray type. If found and within the limit, the storage location is calculated based on the sound ray type and the current count, and all sound ray parameters (including transmitter / transmission identifier, storage location, Doppler shift, and absorption loss) are stored in the output matrix. After storage is complete, create and save the delay dictionary as part of the output matrix. The first row (delay) vector serves as the historical reference for matching in the next frame.

[0099] In subsequent iterations, when the input parameter is false, path tracing logic is executed. A boolean array is initialized to mark which historical slots were successfully updated in the current frame. Each vocal ray in the current frame is traversed, performing local search and matching: first, the range is determined based on the vocal ray type. Then, delay matching is performed; within this range, a match is successful if the delay difference is less than the delay matching threshold. After a successful match, the output matrix for that vocal ray is updated. The relevant parameters in the time delay dictionary are used; if the sound line does not find a match in the time delay dictionary, the first empty slot within the range of this type is searched, and the sound line is treated as a new path and stored in this empty slot. Finally, the disappearing path is virtualized. All slots in the time delay dictionary are traversed; if the initial parameter > 0 (historically existing), but the initialized boolean array is false (not updated in the current frame), then the path is determined to be a disappearing path. For disappearing paths, in the output matrix... Virtualization operations are performed within the process. This involves preserving latency and setting maximum loss. This approach maintains the integrity of the data structure while ensuring that the path does not participate in the signal calculation of the current frame, thus achieving continuous tracking and stable output of channel parameters.

[0100] S6: Superimpose the direct wave signal, target echo signal, reverberation time series, and ocean noise model to obtain the received signal of the bistatic sonar target detection system.

[0101] The source signal, transmitting station information, and receiving station information of the transmitting transducer are input into the unit scattering model to obtain the reverberation time series, and the reverberation time series is input into the receiving transducer array.

[0102] The source signal, transmitter information, and receiver information of the transmitting transducer are input into the direct wave channel H1 (transmitter-receiver) to obtain the direct wave signal, which is then input into the receiving transducer array.

[0103] The source signal, transmitter station information, and target information of the transmitting transducer are input into the target echo channel H2 (transmitter station-target) to obtain the target incident wave. The target scattering wave is then input into the target scattering model to obtain the target scattered wave. The target scattered wave, receiver station information, and target information are then input into the target echo channel H3 (target-receiving station) to obtain the target echo signal. The target echo signal is then input into the receiver transducer array.

[0104] The ocean noise model is also input into the receiving transducer array. The reverberation time series, direct wave signal, target echo signal, and ocean noise model are linearly superimposed to obtain the received signal of the bistatic sonar target detection system. This signal completely reproduces the combined effects of the target, environment, and interference, and can serve as an effective input for subsequent processing and analysis in this application.

[0105] Figure 10A visualization of a bistatic sonar system for target detection was presented. The platform allows for customization of the trajectories of the transmitter, receiver, and target, enabling simulation experiments on moving platforms and moving targets, thus improving the flexibility and applicability of the simulation platform.

[0106] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0107] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application 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. Such 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 this application, and should all be included within the protection scope of this application.

Claims

1. A method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment, characterized in that, Includes the following steps: A three-dimensional dynamic sea surface is constructed based on the JONSWAP spectrum and SWAP direction spectrum; An interface scattering model and a sea surface bubble model are constructed to calculate the interface scattering intensity and the bubble cloud scattering intensity, respectively. Combining the interface scattering intensity and the bubble cloud scattering intensity, a unit scattering model is constructed to divide the scatterers on the seabed and sea surface into units, thereby obtaining the reverberation time series. A marine noise model is constructed by combining turbulent pressure fluctuation noise, shipping noise, wind noise, rain noise, and thermal noise; a target scattering characteristic model is constructed based on sound scattering theory. Based on the Bellhop ray acoustic model, a channel structure is constructed, and the time-varying channel is corrected using a path management method to obtain the direct wave signal and the target echo signal. The direct wave signal, the target echo signal, the reverberation time series, and the ocean noise model are superimposed to obtain the received signal of the bistatic sonar target detection system receiving station.

2. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The process of correcting time-varying channels using the path management method includes: Based on the number of reflections from the sea surface and the seabed, sound rays are classified into types, output matrices are assigned to each type, and type ranges are set. The initial vocal parameters are stored in the output matrix, the time delay of the initial vocal parameters is extracted, and a time delay dictionary is constructed. According to the stated ray type, the corresponding range of the output matrix is ​​locked. The path matching and the update of the ray parameters are completed according to the time delay matching threshold. The unmatched ray is allocated an empty slot within the range of the stated type as a new path. The disappearing path is virtualized. The time delay setting is retained to maximize loss. The time-varying channel is corrected.

3. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The channel structure includes a direct wave channel H1, a target echo channel H2, the target scattering characteristic model, and a target echo channel H3; The transmitted signal is transmitted through the direct wave channel H1 to obtain the direct wave signal; The transmitted signal is transmitted through the target echo channel H2 to obtain the target incident wave, which is then input into the target scattering characteristic model to obtain the target scattered wave. The target scattered wave is then input into the target echo channel H3 to obtain the target echo.

4. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The process of constructing the target scattering characteristic model includes: Determine the target's geometric characteristics, material acoustic parameters, surrounding medium acoustic parameters, and incident wave conditions; For a spherical target, the total velocity potential is expanded into a basis function in spherical coordinates based on the Helmholtz equation. The velocity potential of the incident wave is expanded to obtain the incident wave expansion coefficient. The relationship between the incident wave expansion coefficient and the scattered wave expansion coefficient is established by the Q matrix method to obtain the scattered wave expansion coefficient. The far-field scattering morphology function and target intensity are calculated based on the scattered wave expansion coefficient to construct a target scattering characteristic model for a spherical target. For a finite-length cylindrical target, the total scattered field is decomposed into side scattering and end scattering. The side scattering function and end scattering function are modeled and solved to obtain the side scattering function and end scattering function respectively. The total scattering function is obtained by superimposing them and generating a target scattering characteristic model in which the target intensity varies with frequency and observation angle.

5. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 4, characterized in that, For the side scattering, the differential unit of the finite-length cylindrical target is equivalent to the differential unit of an infinitely long cylinder with the same radius. The scattering coefficient is determined according to the Bessel function, Hankel function and boundary conditions, and then substituted into the scattering wave function to obtain the side scattering function. For the end-face scattering, based on the modified Kirchhoff integral, the reflection coefficient of each unit is equivalent to the reflection coefficient of an infinite plane. The scattered wave in the shadow region of the scatterer is set to zero. The end-face scattering function is obtained by combining the density ratio and the sound speed ratio.

6. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The process of constructing the interface scattering model includes: Define the scattering intensity formula and the geometric characteristics and acoustic parameters of the scattered wave and the incident wave vector. Based on the geometric characteristics and acoustic parameters of the scattered wave and the incident wave vector, calculate the component differences between the scattered wave and the incident wave vector in the horizontal and vertical directions. A two-dimensional roughness spectrum with two parameters is used to characterize the interface roughness, and an incoherent scattering cross section containing the physical characteristics of the interface is constructed using the small slope approximation method. For the seabed and sea surface, the incoherent scattering cross sections adapted to the interface roughness and interface physical characteristics are calculated respectively. Substituting these cross sections into the scattering intensity formula, the interface scattering intensity is output, thus completing the construction of the interface scattering model.

7. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The formula for calculating the scattering intensity of the bubble cloud is: ； In the formula, For acoustic wavenumber, Let be the vertical wavenumber of the incident sound field. Let be the vertical wavenumber of the scattered sound field. This represents the depth of friction due to air friction.

8. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The process of constructing the unit scattering model includes: Based on the bistatic coordinate system and the seabed and sea surface, an equal time delay surface is constructed, and several scattering units are obtained by dividing the space according to the radial step size and the azimuth step size. Based on the horizontal distance, area, time delay, incident grazing angle, and scattering grazing angle of each scattering unit, the scattering term, propagation term, and contribution to reverberation of each scattering unit are calculated, and the contributions are superimposed to obtain the reverberation time series.

9. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The formula for obtaining the reverberation time series is: ； In the formula, For reverberation time series, x-axis coordinate For time, To give every contribution Introduced random phase, The number of scattering rings. The number of scattering units. For the first The scattering ring of the th scattering ring The time delay of the scattered echo corresponding to each scattering unit.

10. The method for constructing a simulation platform for bistatic sonar self-interference signals in a time-varying marine environment as described in claim 1, characterized in that, The process of constructing a three-dimensional dynamic sea surface includes: determining the amplitude and angular frequency of the cosine wave based on the JONSWAP spectrum, determining the direction angle of the cosine wave based on the SWAP direction spectrum, and superimposing the amplitude, angular frequency, and direction angle of the cosine wave to obtain the three-dimensional dynamic sea surface.

Images