A method for simulating reverberation of active sonar based on directivity

Abstract

The application relates to a kind of active sonar reverberation simulation methods based on directivity, comprising the following steps: obtaining the ocean environment parameters required for simulation, the working parameters of active sonar system and the transmission pitch angle of current working condition;Based on the ocean environment parameters and the working parameters, configure the ray acoustics model, and the grazing angle calculation range of the transmission sound ray in the ray acoustics model is expanded to the angular range greater than the calibration beam opening angle of the active sonar system.The application ensures that under the condition of large dynamic range transmission pitch angle, the simulation result can perfectly reproduce all reverberation components including sea surface and seabed, thereby significantly improving the physical authenticity and prediction accuracy of reverberation simulation.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic signal processing and marine acoustic simulation technology, specifically relating to a directional active sonar reverberation simulation method. Background Technology

[0002] Reverberation is a major background disturbance for active sonar operating in interface-constrained waveguides, and its accurate simulation is of great significance for sonar performance evaluation, signal processing algorithm verification, and marine environmental parameter inversion. Currently, the mainstream reverberation simulation methods are mainly divided into two categories: normal mode models based on wave theory and unit scattering models based on ray acoustics.

[0003] Ray-based acoustic models are widely used in engineering practice due to their advantages such as high computational efficiency, clear physical images, and ease of handling complex boundary conditions. Among them, the unit scattering reverberation simulation method based on the Bellhop ray model is the closest existing technical solution. The technical route of this solution is as follows: First, using the ray tracing operation mode of the Bellhop model, the intrinsic sound ray information (including amplitude, time delay, and incident / exit grazing angle) from the transmitting array to each scattering surface element and from each scattering surface element to the receiving array is calculated; second, based on Lambert's scattering law or a more complex interface scattering model, all possible "emission-scattering-reception" sound ray combinations are traversed, and the contribution of each path to the reverberation impact response is calculated; finally, the reverberation impact response is convolved with the transmitted signal to generate a time-domain reverberation signal.

[0004] However, in conventional implementations of existing solutions, the sound source is typically assumed to be a point source with isotropic radiation characteristics, meaning that emitted sound rays in all directions have the same initial amplitude. Alternatively, in a more simplified approach, only the ray clusters within a finite angular domain near the sonar main beam direction are calculated, while the sidelobe energy outside the main beam is completely ignored. This simplified treatment of sonar emission directivity constitutes a fundamental physical flaw in existing technical solutions.

[0005] The traditional reverberation simulation method based on ray acoustics described above has the following obvious drawbacks when applied to active sonar systems with obvious emission directionality, which are derived from causal relationships:

[0006] Systematic Missing Reverberation Components Due to Limited Transmitted Sound Ray Angular Domain: Traditional methods, in order to reduce computational load or based on idealized beam assumptions, typically limit the search range of the grazing angle of the transmitted sound rays to near the opening angle of the main beam. This results in, when the preset sonar elevation angle is large, all the transmitted sound rays involved in the calculation point downwards to the seabed, with no ray grazing towards the sea surface. This directly leads to the sea surface reverberation component contributing zero to the simulated reverberant impact response.

[0007] The mismatch between simulated and measured energy ratios caused by neglecting sidelobe and beam edge energy: In the directivity pattern of an actual sonar transducer array, in addition to the energy-concentrated main lobe, there are also side lobes and transition band energy at the edges of the main lobe. Even if the main beam is pointed towards the seabed, the leakage energy from the side lobes or beam edges will still reach the sea surface and produce a weak, receivable sea surface reverberation. Existing simulation methods ignore this physical fact, concentrating all transmitted energy equivalently in the direction of the main lobe, resulting in a significant discrepancy between the simulated energy ratio of seabed reverberation and sea surface reverberation and the measured data.

[0008] Oversimplification of the sound source model leads to reduced accuracy in subsequent applications: The aforementioned model mismatch causes deviations between the simulated reverberation signal and the actual physical process in both the time-domain arrival structure and the frequency-domain interference pattern. When this simulation method is further applied to sonar parameter calibration or environmental parameter inversion based on the matched field principle, the inherent error of the simulation model will directly translate into a fundamental deviation in the inversion results, limiting the application potential of reverberation information in refined underwater acoustic signal processing. Summary of the Invention

[0009] The technical problem to be solved by this invention is to address the issues of missing physical components and model mismatch in active sonar reverberation simulation caused by neglecting the vertical beam directivity of the actual transducer array. This invention provides a directivity-based active sonar reverberation simulation method that can accurately simulate the directivity effect of the sonar transmission beam. This method ensures that, under conditions of large dynamic range transmission elevation angles, the simulation results can completely reproduce all reverberation components, including those on the sea surface and seabed, thereby significantly improving the physical realism and prediction accuracy of the reverberation simulation.

[0010] The technical solution of this invention is to provide a directional active sonar reverberation simulation method, comprising the following steps:

[0011] Obtain the marine environmental parameters, operating parameters of the active sonar system, and the launch elevation angle under the current operating conditions required for the simulation;

[0012] Based on the marine environmental parameters and the operating parameters, a ray acoustic model is configured, and the calculation range of the grazing angle of the emitted sound rays in the ray acoustic model is extended to an angle range greater than the calibration beam opening angle of the active sonar system.

[0013] The ray acoustic model is invoked to calculate and store the intrinsic ray information of each emitted sound ray reaching the scattering boundary within the extended grazing angle range. The intrinsic ray information includes at least the sound pressure transfer function and the grazing angle.

[0014] According to a preset directivity function, amplitude-weighted compensation is applied to each of the emitted sound rays within the extended grazing angle range. The value of the amplitude-weighted compensation is related to the degree of deviation of the grazing angle of the emitted sound ray from the emission pitch angle.

[0015] Based on the weighted compensation of the emitted sound ray and the scattering characteristics of the scattering boundary, a reverberant impact response is synthesized;

[0016] The reverberation impact response is convolved with a preset transmitted signal waveform to generate a time-domain simulated reverberation signal.

[0017] This invention corrects the simplified description of the emitted sound field in traditional simulation models by extending the angular domain of the emitted sound ray calculation and introducing amplitude-weighted compensation based on the directivity function. The invention aims to construct a higher-fidelity reverberation simulation model that can accurately and completely reproduce all reverberation components, including those on the sea surface and seabed, and their relative energy relationships under arbitrary emission pitch angles, thereby overcoming the inherent defects of existing methods such as missing reverberation components and energy ratio mismatch.

[0018] Preferably, the calculation range of the grazing angle of the emitted sound rays in the ray acoustic model is extended to an angle range greater than the calibration beam opening angle of the active sonar system, specifically as follows:

[0019] The calculation range of the glancing angle of the emitted sound ray is set to... , The launch elevation angle under current operating conditions. This is the preset extension angle value.

[0020] Preferably, the step of applying amplitude-weighted compensation to each emitted sound ray within the extended grazing angle range according to a preset directivity function specifically involves:

[0021] In the stage of synthesizing the reverberant impact response, for each emitted sound ray involved in the calculation, its corresponding glancing angle is obtained;

[0022] Calculate the directionality coefficient corresponding to the grazing angle based on the preset directionality function;

[0023] The sound pressure transfer function of the emitted sound ray is corrected using the directivity coefficient as a weighting factor.

[0024] Preferably, the synthesized reverberant impact response specifically includes:

[0025] The synthesized reverberant impact response specifically includes:

[0026] Iterate through all preset scattering elements;

[0027] For the current scattering element, combine all incident sound rays from the transmitting array to the element and all scattered sound rays from the element to the receiving array;

[0028] The reverberant impact response is calculated using the following formula:

[0029]

[0030] in, This represents the reference sound intensity per unit distance from the sound source. As a directional compensation factor, For the first The sound pressure transfer function of an incident sound ray. The interface scattering coefficient is... Let be the area of ​​the scattering surface element.

[0031] Preferably, the interface scattering coefficient is calculated based on Lambert's scattering law, and the calculation formula is as follows:

[0032]

[0033] in, The scattering coefficient is... The incident grazing angle, The outgoing sweep angle.

[0034] Preferably, the ray acoustic model is the Bellhop ray model, and the intrinsic sound ray information is obtained through its ray tracing operation mode. The intrinsic sound ray information includes the arrival time, sound pressure amplitude and glancing angle of each sound ray.

[0035] Preferably, the transmitted signal waveform is a linear frequency modulated signal, a CW pulse signal, or a hyperbolic frequency modulated signal.

[0036] Furthermore, the active sonar system is a transceiver system, the transmitted sound ray is the sound ray originating from the transmitting array, and the scattered sound ray is the sound ray arriving at the receiving array from the scattering surface element.

[0037] Compared with the prior art, the present invention has the following advantages:

[0038] This invention can improve the physical accuracy of the emitted sound field modeling, specifically in the following ways:

[0039] First, the physical completeness of the reverberation components. The energy emitted by actual sonar is continuously distributed in the spatial angular domain, including the main lobe and side lobes. Traditional reverberation simulation methods discretize the emitted energy into constant-amplitude sound rays within a finite angular domain, neglecting or truncating side lobes and edge energy. This invention, by extending the angular domain, incorporates the directional beam of the actual sonar into the calculation, avoiding the information truncation caused by traditional simulation methods. Therefore, the simulation results are physically complete, and the problem of systematically missing specific components no longer exists.

[0040] Second, the precise proportion of reverberation energy. This invention precisely quantifies the energy differences of active sonar transmitted signals at different angles by introducing directional weighting. Therefore, the energy ratios and relative relationships of each path component in the simulated reverberation are accurate and highly consistent with the actual reverberation signal.

[0041] Third, the reliability of subsequent applications is improved. Because the integrity and high fidelity of the model are guaranteed, subsequent advanced applications based on this simulation method (such as sonar parameter calibration based on the matching field principle and environmental parameter inversion) will be built on a more accurate theoretical foundation, thereby significantly improving the forecast accuracy and reliability of subsequent work. Attached Figure Description

[0042] Figure 1 This is a comparison chart of the two simulation methods.

[0043] Figure 2 This is a simulation schematic.

[0044] Figure 3 This is the algorithm flowchart.

[0045] Figure 4 The sound velocity profile used for the simulation example.

[0046] Figure 5 Let be the hypothetical active sonar pointing function.

[0047] Figure 6 is a comparison of simulation results using a 60-degree opening angle and a 120-degree opening angle.

[0048] Figure 7 is a comparison of simulation results with only the expanded opening angle and the directional weighted result.

[0049] Figure 8 shows a comparison of simulation results before and after the improvement under a pitch angle of 40°. Detailed Implementation

[0050] The present invention will be further described below with reference to the accompanying drawings and specific embodiments:

[0051] Figure 1 This is a comparison chart of simulation results between the method of this invention and the traditional method. For example... Figure 1As shown, traditional methods limit the calculation range of the emitted sound ray glancing angle to near the opening angle of the main beam, resulting in the complete absence of the sea surface reverberation component. However, the method of this invention, by expanding the emission angle domain and introducing directional weighted compensation, can simultaneously reproduce both sea surface reverberation and seabed reverberation, and the simulation results are more complete in terms of physical composition.

[0052] like Figure 2 As shown, this invention discloses a directional active sonar reverberation simulation method based on ray acoustics theory and Lambert's scattering law to achieve interface reverberation modeling in deep-sea environments. The simulation principle is as follows:

[0053] The core formula is as follows:

[0054]

[0055] in: This represents the reference sound intensity per unit distance from the sound source. Let be the area of ​​the scattering surface element. Let be the sound pressure transfer function along the incident path. As a directional compensation factor, it is the core weighting term of this invention. Let be the sound pressure transfer function of the scattering path. The interface scattering coefficient is based on Lambert's law or other models, and is related to the incident grazing angle. and scattering glancing angle The relevant calculation method is as follows:

[0056]

[0057] in, For the scattering coefficient, in the reverberation simulation of relatively soft muddy and sandy seabed, it satisfies... , In the simulation of sea surface reverberation, the scattering intensity is stronger than that of most seabed areas, so the upper limit of seabed scattering is taken. , .

[0058] The incident grazing angle can be obtained through Bellhop simulation. With the angle of attack Incident sound pressure transfer function With the scattered sound pressure transfer function These correspond to Arr.Rcvrangle and Arr.A in the Bellhop A running mode (ray tracing running mode).arr file, respectively.

[0059] like Figure 3 As shown, the overall process of this algorithm is as follows:

[0060] Step 1: Obtain the acoustic environment parameters required for the simulation. Obtain the necessary marine environmental parameters for the simulation using historical data, measured data, or empirical formulas. These mainly include: sea depth, acoustic characteristics of the sea surface and seabed (such as seabed sediment type, density, sound velocity, absorption coefficient; sea surface roughness, scattering coefficient, etc.), and the sound velocity profile in the seawater. These parameters form the basis for constructing the Bellhop simulation environment file (.env).

[0061] Step 2: Obtain transmission parameters. Define the operating parameters of the active sonar system. These mainly include: the deployment depth of the transmitting and receiving arrays, the directivity function of the sonar system, the center frequency, bandwidth, pulse width, signal type, and transmission power of the transmitted signal. These parameters will be used to generate the simulated transmission signal and configure the source and receiver properties in the Bellhop simulation.

[0062] Step 3: Calculation of the ray model under the extended launch angle domain. Let the launch elevation angle under the current operating condition be... Configure the environment file (.env) for the Bellhop ray acoustic model. For a separate transmit / receive system, separate propagation files need to be configured for "transmit array → sea surface / seabed" and "sea surface / seabed → receiver array". The key setting is that the calculation range for the grazing angle of the sound ray originating from the transmit array should be set to...

[0063] In the formula, This is the preset extension angle value.

[0064] Call the Bellhop model (run mode A) to calculate and store all intrinsic sound ray information arriving at the scattering boundary, including: arrival time, sound pressure amplitude A, incident / exit grazing angle, etc.

[0065] Step 4: Directivity-weighted reverberant impact response synthesis. Iterate through all scattering elements. For each element, combine all incident sound rays arriving at that element from the emission array. and the scattered sound rays reaching the receiving array from this element. The reverberation intensity contributed by this path is calculated by the following formula:

[0066]

[0067] In the formula As a directional compensation factor, it ensures the accuracy of the simulation results and is the core weighting term of this invention.

[0068] Step 5: Generating the simulated reverberation signal. The reverberation impact response sequence, which includes directivity compensation, calculated in Step 4, is convolved with the set transmitted signal waveform to obtain the final, high-fidelity time-domain simulated reverberation signal. .

[0069] Comparison of simulation results before and after the method improvement

[0070] Here, a linear frequency modulated signal with a center frequency of 2500 Hz, a bandwidth of 300 Hz, and a pulse width of 6 s is used as an example for algorithm simulation. In the example, the sonar directivity function is a hypothetical value rather than a real value, and the sonar elevation angle is horizontal.

[0071] Figure 4 This is the sound velocity profile used in this embodiment.

[0072] Figure 5 This is the assumed active sonar pointing function in this embodiment.

[0073] Figure 6 shows a comparison of simulation results using a 60-degree opening angle and a 120-degree opening angle (Figure 6(a) is for a 60-degree opening angle, and Figure 6(b) is for a 120-degree opening angle). It can be seen that simply expanding the simulation opening angle resulted in a significant difference in the simulation results. This is because the missing acoustic rays emitted towards the sea surface or seabed have been filled in; however, the simulation results still deviate considerably from reality due to the lack of sonar directivity function weighting.

[0074] Figure 7 shows a comparison of simulation results with only widened opening angle and directional weighting (Figure 7(a) shows only widened opening angle, Figure 7(b) shows with directional weighting). The comparison shows that, because the sound ray at a large angle is the steepest, the round-trip distance to the seabed is the shortest, and it reaches the receiver first. Therefore, after directional weighting, the sound intensity of the seabed reverberation in the initial arrival phase (6s-15s) is lower than the unweighted simulation result. This simulation result is closer to reality.

[0075] Figure 8 shows a comparison of simulation results before and after the improvement under a pitch angle of 40° (Figure 8(a) is before the improvement, and Figure 8(b) is after the improvement using the method of this invention). Under the more extreme pitch angle of 40°, the improvement of this simulation method is even more significant. It can be seen that the previously missing sea surface reverberation is filled in, and the initial value of the seabed reverberation is also more accurate.

[0076] It is evident that, after improvements such as widening the opening angle and adding directional weighting, the traditional reverberation simulation method based on the acoustic toolbox has achieved more reliable results in active sonar reverberation simulation. This invention has successfully constructed a reverberation simulation model with higher fidelity, laying a solid foundation for further applications.

[0077] The above description only illustrates preferred embodiments of the present invention and should not be construed as limiting the scope of the claims. All equivalent modifications made using this specification are included within the patent protection scope of the present invention.

Claims

1. A method for simulating reverberation of directional active sonar, characterized in that, Includes the following steps: Obtain the marine environmental parameters, operating parameters of the active sonar system, and the launch elevation angle under the current operating conditions required for the simulation; Based on the marine environmental parameters and the operating parameters, a ray acoustic model is configured, and the calculation range of the grazing angle of the emitted sound rays in the ray acoustic model is extended to an angle range greater than the calibration beam opening angle of the active sonar system. The ray acoustic model is invoked to calculate and store the intrinsic ray information of each emitted sound ray reaching the scattering boundary within the extended grazing angle range. The intrinsic ray information includes at least the sound pressure transfer function and the grazing angle. According to a preset directivity function, amplitude-weighted compensation is applied to each of the emitted sound rays within the extended grazing angle range. The value of the amplitude-weighted compensation is related to the degree of deviation of the grazing angle of the emitted sound ray from the emission pitch angle. Based on the weighted compensation of the emitted sound ray and the scattering characteristics of the scattering boundary, a reverberant impact response is synthesized; The reverberation impact response is convolved with a preset transmitted signal waveform to generate a time-domain simulated reverberation signal.

2. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The extension of the calculation range of the grazing angle of the emitted sound rays in the ray acoustic model to an angle range greater than the calibration beam opening angle of the active sonar system specifically includes: The calculation range of the glancing angle of the emitted sound ray is set to... , The launch elevation angle under current operating conditions. This is the preset extension angle value.

3. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The step of applying amplitude-weighted compensation to each emitted sound ray within the extended grazing angle range according to a preset directivity function specifically involves: In the stage of synthesizing the reverberant impact response, for each emitted sound ray involved in the calculation, its corresponding glancing angle is obtained; Calculate the directionality coefficient corresponding to the grazing angle based on the preset directionality function; The sound pressure transfer function of the emitted sound ray is corrected using the directivity coefficient as a weighting factor.

4. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The synthesized reverberant impact response specifically includes: The synthesized reverberant impact response specifically includes: Iterate through all preset scattering elements; For the current scattering element, combine all incident sound rays from the transmitting array to the element and all scattered sound rays from the element to the receiving array. The reverberant impact response is calculated using the following formula: in, This represents the reference sound intensity per unit distance from the sound source. As a directional compensation factor, For the first The sound pressure transfer function of an incident sound ray. The interface scattering coefficient is... Let be the area of ​​the scattering surface element.

5. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The interface scattering coefficient is calculated based on Lambert's scattering law, and the calculation formula is as follows: in, The scattering coefficient is... The incident grazing angle, The outgoing sweep angle.

6. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The ray acoustic model is the Bellhop ray model, and the intrinsic sound ray information is obtained through its ray tracing operation mode. The intrinsic sound ray information includes the arrival time, sound pressure amplitude and glancing angle of each sound ray.

7. The directional active sonar reverberation simulation method according to claim 1, characterized in that, The transmitted signal waveform is a linear frequency modulated signal, a CW pulse signal, or a hyperbolic frequency modulated signal.

8. The directional active sonar reverberation simulation method according to any one of claims 1 to 7, characterized in that, The active sonar system is a transceiver system, the transmitted sound ray is the sound ray originating from the transmitting array, and the scattered sound ray is the sound ray arriving at the receiving array from the scattering surface element.

Images