A modeling and simulation method for the space-time reverberation of broadband signals under a moving platform

Abstract

The present invention discloses a method for modeling and simulating the space-time reverberation of broadband signals on the seabed under a moving platform, comprising the following steps: step one: setting parameters related to the transmitting signal, the ocean environment, the moving platform and the roughness of the seabed; step two: using a network model to arrange the reverberation scattering units on the seabed surface, setting the value range of the scattering units and the spatial position coordinates of each scattering unit; step three: solving the waveform compression parameters of each scattering unit according to the radial motion speed of the moving platform. The present invention solves the problem that the previous seabed reverberation modeling based on the ray model is only used for the prediction of the reverberation level, and does not consider the delay difference caused by the undulating seabed surface and the scaling of the broadband signal waveform caused by the moving platform. It also takes into account the influencing factors such as the roughness of the seabed scattering unit, the ocean environment, the type of transmitting signal and the scaling of the waveform caused by the moving platform, and can naturally reflect the formation mechanism of reverberation.

Description

Technical field:

[0001] The invention relates to the technical field of underwater acoustic engineering, and in particular to a method for modeling and simulating the space-time reverberation of a broadband signal under a moving platform. Background technology:

[0002] In order to counter modern quiet submarines and extract target features, the common anti-submarine means of active sonar today is to transmit low-frequency, high-power broadband signals. From the perspective of information theory, the larger the time-bandwidth product of the transmitted signal, the greater the amount of target information carried by the target echo, which is more conducive to target detection and parameter estimation. At present, the scattered echo of the seabed is an important interference that restricts the detection of long-range targets by active sonar. In order to break through the technical bottleneck of active sonar's anti-strong reverberation interference, modeling and simulation of the seabed reverberation of broadband signals under a moving platform are carried out, which is of great significance to the research on active sonar anti-reverberation technology.

[0003] In order to better suppress reverberation, we must first build a space-time reverberation model to obtain the reverberation time series, and based on this, understand the reverberation characteristics that are different from the echo signal. At present, the main means of obtaining reverberation data is to conduct tank tests, lake tests, and offshore tests. However, it costs a lot to conduct engineering tests to obtain reverberation data, and various features in the test data are fused together, making it difficult to distinguish and separate, and lack a clear physical formation mechanism. Therefore, it is of great significance to complete the model construction and numerical simulation of reverberation and anti-reverberation signal processing.

[0004] In the past, seabed reverberation modeling based on ray models was mainly used to predict the reverberation level. The reverberation model only considered the scattering intensity to describe the roughness of the seabed, without considering the phase information brought by the undulating seabed, and could not reflect other characteristics of the reverberation. At present, the existing seabed reverberation modeling has the following limitations: First, the numerical simulation of seabed reverberation is mostly aimed at narrowband systems, and is not suitable for reverberation data simulation of broadband signals. Second, it cannot take into account factors such as the motion characteristics of the platform, the propagation path, and the roughness of the seabed scattering unit. Therefore, a reverberation modeling method for arbitrary signals that can reflect the roughness of the seabed and the motion characteristics of the platform is needed to meet the requirements of space-time anti-reverberation technology for various types of reverberation data. Summary of the invention:

[0005] The technical problem to be solved by the present invention is to provide a method for modeling and simulating the space-time reverberation of the seabed of broadband signals under a moving platform, which can solve the shortcomings of the existing technology and take into account the roughness of the seabed scattering unit, the motion characteristics of the moving platform, multipath propagation and signal type, etc.; it reflects that the delay difference caused by the undulating seabed surface and the moving platform will affect the seabed reverberation modeling. This method can accurately simulate the reverberation sequence of the rough seabed under the moving platform.

[0006] The technical solution of the present invention is to provide a method for modeling and simulating the space-time reverberation of a broadband signal under the seabed under a moving platform, the method comprising the following steps:

[0007] Step 1: Set the parameters related to the transmission signal, ocean environment, motion platform and seabed roughness;

[0008] Step 2: Use the network model to arrange the reverberation scattering units on the seabed surface, set the value range of the scattering units and the spatial position coordinates of each scattering unit;

[0009] Step 3: Solve the waveform compression parameters of each scattering unit according to the radial motion speed of the motion platform;

[0010] Step 4: Set the scattering coefficient of each scattering unit according to Lambert's scattering law, and set the acoustic path delay difference of each scattering unit according to the roughness of the seabed;

[0011] Step 5: Calculate the optimal weight of the FARROW structure filter according to the fluctuation of the seabed scattering unit, and store the obtained prototype filter parameters;

[0012] Step 6: Input the time delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters, and use the fitted filter parameters to filter the broadband signal with waveform expansion and contraction caused by the Doppler effect to generate a reverberation time series;

[0013] Step 7: Superimpose the time series of all scattering units to obtain the total reverberation waveform.

[0014] Preferably, in step one, the transmission signal parameters include the pulse width, bandwidth, transmission sound source depth and receiving sound source depth of the transmission signal; the ocean environment parameters include the sea depth, water sound speed and the scattering coefficient of the sea surface; the motion platform includes the number of array elements of the receiving array, the movement direction and the movement speed; the seabed roughness parameters include the scattering intensity of the seabed and the undulation size of the rough seabed.

[0015] Preferably, the specific steps of step three are as follows:

[0016] Step 31: Assume that the incident angle of the seafloor scatterer relative to the axial direction is α, the incident angle relative to the velocity direction is θ, and the pitch angle with respect to the coordinate plane is The motion speed of the motion platform is ν, then the radial motion speed of the seafloor scattering unit relative to the motion platform is ν d for

[0017]

[0018] Step 32: Radial motion speed ν of the motion platform d The waveform compression parameter η caused by

[0019]

[0020] Where c is the propagation speed in water;

[0021] Step 33: Assuming that the distance between the scattering unit and the receiving point is d0, the target echo r rec for

[0022]

[0023] Among them, s(t) is the signal emitted by the sound source.

[0024] As a preference, the specific steps of step 4 are as follows:

[0025] Step 41: According to the roughness of the seabed, the scattering coefficient of the scattering unit is set to obey a Gaussian distribution with a mean value of μ. The scattering intensity A(i) of the i-th scattering unit is

[0026]

[0027] in, is the incident angle of the sound wave, ζ is the reflection angle of the sound wave;

[0028] Step 42: Set the acoustic path delay difference Δτ of the i-th scattering unit according to the undulation of the seabed i , Δτ i It obeys the uniform distribution of (τ1,τ2), where τ1 and τ2 are pre-set values.

[0029] As a preference, the specific steps of step five are as follows:

[0030] Step 51: The objective function of fitting the frequency characteristics of the digital delay filter is

[0031] minimax W(ω)|H(e jω )-H d (e jω )|

[0032] Among them, H(e jω ) is the Fourier transform of the ideal infinite length h(n), H d (e jω ) is the target frequency characteristic, W(ω) is the frequency weighting function;

[0033] Step 52: Assume that the range of the fractional delay d is [-0.5, 0.5] and the order of the polynomial fitting is p, then the transfer function H of the delay filter is d (e jω )for:

[0034]

[0035] Among them, C m (n) is the fitting coefficient of the fractional delay filter, and N is the number of taps of the delay filter.

[0036] As a preference, the specific steps of step six are as follows:

[0037] Step 61: Input the delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters

[0038]

[0039] Step 62: Substitute the compression parameter η caused by the Doppler effect into the transmitted signal, and the reverberation time series of the i-th scattering unit is

[0040] r rec =s(η(tt is -t im +Δτ i ))

[0041] Among them, t is and t im are the transmission and reception time of the i-th scattering unit respectively;

[0042] Step 63: Use the filter parameters to filter the i-th reverberation time series r rec Filter the reverberation time series; and multiply the reverberation time series by the sound wave attenuation weight;

[0043]

[0044] Among them, filter(h d ,1,r rec ) represents the filter coefficient h used for fitting d R rec Filtering, R is and R im are the propagation distance and receiving distance respectively, and dA is the scattering area.

[0045] Furthermore, in step 7, the time series of all scattering units are superimposed to obtain the total reverberation waveform.

[0046]

[0047] And analyze its statistical characteristics, frequency characteristics and related characteristics.

[0048] Compared with the prior art, the present invention has the following advantages after adopting the above scheme:

[0049] The present invention solves the problem that the previous seabed reverberation modeling based on the ray model is only used for the prediction of the reverberation level, and does not consider the delay difference caused by the undulating seabed surface and the scaling of the broadband signal waveform caused by the moving platform. It also takes into account the influencing factors such as the roughness of the seabed scattering unit, the marine environment, the type of transmitted signal, and the scaling of the waveform caused by the moving platform, and can naturally reflect the formation mechanism of reverberation. Description of the drawings:

[0050] Figure 1 It is the main flow chart of the modeling and simulation method of the seabed space-time reverberation of broadband signals under the motion platform of the present invention;

[0051] Figure 2 Schematic diagram of four types of primary seafloor scattering models;

[0052] Figure 3 This is the distribution map of seafloor scatterers under the moving platform;

[0053] Figure 4 It is a structure diagram of a variable fractional delay filter with FARROW structure;

[0054] Figure 5 is the amplitude-frequency response curve of the FARROW structure filter;

[0055] Figure 6 It is the phase-frequency response curve of the FARROW structure filter;

[0056] Figure 7 This is the waveform diagram of the simulated reverberation signal;

[0057] Figure 8 To simulate the probability distribution of the instantaneous value of the reverberation signal;

[0058] Fig. 9 To simulate the envelope probability distribution of the reverberation signal;

[0059] Fig.10 This is the spectrum of the seabed reverberation of the broadband signal under motion;

[0060] Fig.11 To simulate the local amplification of the reverberation signal autocorrelation. Specific implementation method:

[0061] The present invention will be further described below with reference to the accompanying drawings:

[0062] like Figure 1 As shown, the modeling and simulation method of the broadband signal seabed space-time reverberation under the motion platform of the present invention specifically includes the following steps:

[0063] Step 1: Set the parameters of the transmission signal, ocean environment, motion platform, and seabed roughness. This example sets the basic parameters: the parameters of the transmission signal are: pulse width T, bandwidth B. The parameters of the ocean environment are: water sound velocity c, scattering coefficient of the sea surface, sound source depth h1, receiving depth h2, sea depth H, and seabed scattering times. The parameters of the motion platform are: driving direction and driving speed. The seabed roughness parameters are: scattering intensity coefficient μ, rough seabed fluctuation size Δτ i Assuming that the sound wave expands as a spherical wave, since the scattering intensity of multiple seafloor scattering contributes little to the reverberation intensity, the present invention only considers four types of single seafloor scattering models. Assuming that the incident angle of the sound wave relative to the seafloor surface is The reflection angle is ζ, R is and R im are the propagation distance and receiving distance of the sound wave respectively. Figure 2 As shown:

[0064] The incident angle of the first type of sound ray is The reflection angle is

[0065] The incident angle of the second type of sound ray is The reflection angle is

[0066] The incident angle of the third type of sound ray is The reflection angle is

[0067] The incident angle of the fourth type of sound is The reflection angle is

[0068] Step 2: Use the network model to arrange the reverberation scattering units on the seabed surface, set the value range of the scattering units and the spatial position coordinates of each scattering unit.

[0069] Step 3: Solve the waveform compression parameters of each scattering unit according to the radial motion speed of the motion platform, as follows:

[0070] Step 31: Assume that the incident angle of the seafloor scatterer relative to the axial direction is α, the incident angle relative to the velocity direction is θ, and the pitch angle with respect to the coordinate plane is The motion speed of the motion platform is ν, then the radial motion speed of the seafloor scattering unit relative to the motion platform is ν d for

[0071]

[0072] Step 32: Radial motion speed ν of the motion platform d The waveform compression parameter η caused by

[0073]

[0074] Where c is the propagation speed in water;

[0075] Step 33: Assuming that the distance between the scattering unit and the receiving point is d0, the target echo r rec for

[0076]

[0077] Among them, s(t) is the signal emitted by the sound source.

[0078] Step 4: Set the scattering coefficient of each scattering unit according to Lambert's scattering law, and set the acoustic path delay difference of each scattering unit according to the roughness of the seabed; the details are as follows:

[0079] Step 41: According to the roughness of the seabed, the scattering coefficient of the scattering unit is set to obey a Gaussian distribution with a mean value of μ. The scattering intensity A(i) of the i-th scattering unit is

[0080]

[0081] in, is the incident angle of the sound wave, ζ is the reflection angle of the sound wave;

[0082] Step 42: Set the acoustic path delay difference Δτ of the i-th scattering unit according to the undulation of the seabed i , Δτ i It obeys the uniform distribution of (τ1,τ2), where τ1 and τ2 are pre-set values.

[0083] Step 5: Calculate the optimal weight of the FARROW structure filter according to the fluctuation of the seabed scattering unit, and store the obtained filter parameters;

[0084] Step 51: The objective function of fitting the frequency characteristics of the digital delay filter is

[0085] minimax W(ω)|H(e jω )-H d (e jω )|

[0086] Among them, H(e jω ) is the Fourier transform of the ideal infinite length h(n), H d (e jω ) is the target frequency characteristic, W(ω) is the frequency weighting function;

[0087] Step 52: Assume that the range of the fractional delay d is [-0.5, 0.5] and the order of the polynomial fitting is p, then the transfer function H of the delay filter is d (e jω )for:

[0088]

[0089] Among them, C m (n) is the fitting coefficient of the fractional delay filter, and N is the number of taps of the delay filter.

[0090] Step 6: Input the delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters, and use the fitted filter parameters to filter the broadband signal with waveform expansion and contraction caused by Doppler to generate a reverberation time series, as follows:

[0091] Step 61: Input the delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters

[0092]

[0093] Step 62: Substitute the compression parameter η caused by the Doppler effect into the transmitted signal, and the reverberation time series of the i-th scattering unit is

[0094] r rec =s(η(tt is -t im +Δτ i ))

[0095] Among them, t is and t im are the transmission and reception time of the i-th scattering unit respectively;

[0096] Step 63: Use the filter parameters to filter the i-th reverberation time series r rec Filter the reverberation time series and multiply the reverberation time series by the sound wave attenuation weight.

[0097]

[0098] Among them, filter(h d ,1,r rec ) represents the filter coefficient h d R rec Filtering, R is and R im are the propagation distance and receiving distance respectively, and dA is the scattering area.

[0099] Step 7: Superimpose the time series of all scattering units to obtain the total reverberation waveform.

[0100]

[0101] To facilitate understanding, further examples are given.

[0102] Step 1: Set the parameters of the transmission signal, ocean environment, motion platform, and seabed roughness;

[0103] Set the parameters such as the transmitting signal, ocean environment, motion platform, and seabed roughness. This example sets the basic parameters:

[0104] Select linear frequency modulation signal as the transmission signal, with specific parameters: pulse width T = 400ms, initial frequency 500Hz, end frequency 1500Hz; the parameters of the ocean environment are: water sound velocity c = 1500m / s, sound source depth h1 = 10m, receiving depth h2 = 10m, and sea depth H = 200m. The parameters of the motion platform are: driving speed ν = 15m / s. Only four types of primary seafloor scattering models are considered, such as Figure 2 As shown;

[0105] Step 2: Use the network model to arrange the reverberation scattering units on the seabed surface, set the value range of the scattering units and the spatial position coordinates of each scattering unit;

[0106] Step 3: Solve the waveform compression parameters of each scattering unit according to the radial motion speed of the motion platform; the waveform compression parameters of each scattering unit refer to Figure 3 The distribution map of seabed scatterers under the moving platform is solved.

[0107] Step 4: Set the scattering coefficient of each scattering unit according to Lambert's scattering law, and set the acoustic path delay difference of each scattering unit according to the roughness of the seabed.

[0108] A(i) follows a Gaussian distribution with a mean of μ = 0.5, Δτ i Obey the uniform distribution of (τ1, τ2), τ1 = -0.3 and τ2 = 0.3.

[0109] Step 5: Calculate the optimal weight of the FARROW structure filter according to the fluctuation of the seabed scattering unit, and store the obtained filter parameters;

[0110] Figure 4 This is the principle block diagram of the FARROW structure filter. The number of taps of the filter is set to 15, the Lagrange polynomial fitting order is 5, and the cutoff normalized frequency is 0.6. Figure 5 and Figure 6 The amplitude-frequency response and phase-frequency response curves of the FARROW structure filter.

[0111] Step 6: Input the time delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters, and use the fitted filter parameters to filter the broadband signal with waveform expansion and contraction caused by Doppler to generate a reverberation time series;

[0112] Step 7: Superimpose the time series of all scattering units to obtain the total reverberation waveform, and analyze its statistical characteristics, frequency characteristics and related characteristics;

[0113] Figure 7 The waveforms of the transmitted signal and the simulated reverberation signal are shown in Figure 2. The frequency statistics of the simulated broadband signal time series are obtained as follows: Figure 8 and Fig. 9 The instantaneous value and envelope probability distribution shown in the figure are used to analyze the dispersion characteristics of the reverberation signal. The Fourier transform of the time series is obtained as follows: Fig.10 The reverberation spectrum shown in the figure is Fig.11 They are the autocorrelation local amplification curves of the transmitted signal and the simulated reverberation signal respectively.

[0114] The present invention comprehensively considers factors such as the roughness of the seabed scattering unit, the motion characteristics of the moving platform, multipath propagation and signal type. Since the frequency of the broadband signal is no longer constant and the delay and phase of the broadband signal are no longer in a linear relationship, a delay filter is used to introduce a delay difference to describe the fluctuation of the seabed surface. At the same time, the compression parameters of each scattering unit relative to the moving platform are solved and substituted into the transmission signal to realize the reverberation modeling of the moving platform.

[0115] The above is only an explanation of the preferred embodiments of the present invention, which should not be construed as a limitation on the claims. Any equivalent structure or equivalent process changes made using the present invention specification are included in the patent protection scope of the present invention.

Claims

1. A method for modeling and simulating the space-time reverberation of broadband signals under a moving platform, characterized by: The method comprises the following steps: Step 1: Set the parameters related to the transmission signal, ocean environment, motion platform and seabed roughness; Step 2: Use the network model to arrange the reverberation scattering units on the seabed surface, set the value range of the scattering units and the spatial position coordinates of each scattering unit; Step 3: Solve the waveform compression parameters of each scattering unit according to the radial motion speed of the motion platform; Step 4: Set the scattering coefficient of each scattering unit according to Lambert's scattering law, and set the acoustic path delay difference of each scattering unit according to the roughness of the seabed; Step 5: Calculate the optimal weight of the FARROW structure filter according to the fluctuation of the seabed scattering unit, and store the obtained prototype filter parameters; Step 6: Input the time delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters, and use the fitted filter parameters to filter the broadband signal with waveform expansion and contraction caused by the Doppler effect to generate a reverberation time series; Step 7: Superimpose the time series of all scattering units to obtain the total reverberation waveform; The specific steps of step three are as follows: Step 31: Assume that the incident angle of the seafloor scatterer relative to the axial direction is α, the incident angle relative to the velocity direction is θ, and the pitch angle with respect to the coordinate plane is The motion speed of the motion platform is ν, then the radial motion speed of the seafloor scattering unit relative to the motion platform is ν d for Step 32: Radial motion speed ν of the motion platform d The waveform compression parameter η caused by Where c is the propagation speed in water; Step 33: Assuming that the distance between the scattering unit and the receiving point is d0, the target echo r rec for Among them, s(t) is the signal emitted by the sound source; The specific steps of step 4 are as follows: Step 41: According to the roughness of the seabed, the scattering coefficient of the scattering unit is set to obey a Gaussian distribution with a mean value of μ. The scattering intensity A(i) of the i-th scattering unit is in, is the incident angle of the sound wave, ζ is the reflection angle of the sound wave; Step 42: Set the acoustic path delay difference Δτ of the i-th scattering unit according to the undulation of the seabed i , Δτ i It obeys the uniform distribution of (τ1, τ2), where τ1 and τ2 are pre-set values; The specific steps of step five are as follows: Step 51: The objective function of fitting the frequency characteristics of the digital delay filter is minimax W(ω)|H(e jω )-H d (e jω )| Among them, H(e jω ) is the Fourier transform of the ideal infinite length h(n), H d (e jω ) is the target frequency characteristic, W(ω) is the frequency weighting function; Step 52: Assume that the range of the fractional delay d is [-0.5, 0.5] and the order of the polynomial fitting is p, then the transfer function H of the delay filter is d (e jω )for: Among them, C m (n) is the fitting coefficient of the fractional delay filter, and N is the number of taps of the delay filter; The specific steps of step six are as follows: Step 61: Input the delay difference of each scattering unit into the prototype filter to obtain the fitted filter parameters Step 62: Substitute the compression parameter η caused by the Doppler effect into the transmitted signal, and the reverberation time series of the i-th scattering unit is r rec =s(η(t-t is -t im +Δτ i )) Among them, t is and t im are the transmission and reception time of the i-th scattering unit respectively; Step 63: Use the filter parameters to filter the i-th reverberation time series r rec Filter the reverberation time series; and multiply the reverberation time series by the sound wave attenuation weight; Among them, filter(h d ,1,r rec ) represents the filter coefficient h used for fitting d R rec Filtering, R is and R im are the propagation distance and receiving distance respectively, and dA is the scattering area.

2. The method for modeling and simulating the space-time reverberation of a broadband signal under a moving platform according to claim 1, characterized in that: In step one, the transmission signal parameters include the pulse width, bandwidth, transmission source depth and receiving source depth of the transmission signal; the ocean environment parameters include the sea depth, water sound speed and the scattering coefficient of the sea surface; the motion platform includes the number of array elements of the receiving array, the movement direction and the movement speed; the seabed roughness parameters include the scattering intensity of the seabed and the undulation size of the rough seabed.

3. The method for modeling and simulating the space-time reverberation of a broadband signal under a moving platform according to claim 1, characterized in that: In step 7, the time series of all scattering units are superimposed to obtain the total reverberation waveform. And analyze its statistical characteristics, frequency characteristics and related characteristics.

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