A wideband array gain prediction method based on sound field spatial correlation correction

Abstract

This invention discloses a broadband array gain prediction method based on acoustic field spatial correlation correction. This method utilizes marine environmental data for acoustic field modeling, calculates the channel frequency response function from the target to each array element position, estimates the correlation coefficient of the received signal after channel distortion, and forms a signal correlation coefficient matrix. Furthermore, it uses an isotropic noise field model to estimate the inter-channel noise correlation coefficient after the processed frequency band deviates from the ideal frequency, forming a noise correlation coefficient matrix. Finally, it uses the two correlation coefficient matrices to calculate the array gain. This method can effectively reflect the coupling between the underwater acoustic array and the actual marine environment during operation, and can improve the accuracy of the array gain calculation results.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic signal processing, specifically relating to a broadband array gain prediction method based on acoustic field spatial correlation correction. Background Technology

[0002] In the field of modern underwater acoustic signal processing, array signal processing technology often plays a crucial role. In sonar systems, beamforming technology is commonly used to improve the signal-to-noise ratio of the received signal by utilizing the spatial correlation of the array received signal. In underwater target detection, it is essential to accurately calculate the array gain and understand the detection performance of the sonar system in the actual environment. This is of great significance for the combined application of tactics and techniques.

[0003] Array gain estimation is a crucial component of sonar equipment decision support technology. In conventional sonar signal processing, the ocean waveguide environment is often treated as an isotropic homogeneous environment, with array spacing satisfying the half-wavelength condition—meaning the received target signal is perfectly correlated while background noise is completely uncorrelated. However, the actual ocean environment is affected by internal waves, wind, waves, and surface navigation, causing the underwater acoustic channel to exhibit time- and space-varying characteristics, leading to reduced signal spatiotemporal correlation. Sonar systems often utilize beamforming technology, which improves the signal-to-noise ratio (SNR) by leveraging the spatial correlation of the received signal. However, as the sonar frequency decreases and the element spacing increases, the signal correlation between elements decreases, causing the array processing gain to deviate from the theoretical value and reducing the accuracy of sonar detection performance assessment. Therefore, studying the impact of sound field spatiotemporal correlation on the spatiotemporal processing gain of sonar systems to improve the accuracy of detection performance assessment is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a broadband array gain prediction method based on acoustic field spatial correlation correction, so as to solve the problem in the background art where the working environment of underwater acoustic arrays is inconsistent with the ideal environment, resulting in a decrease in the accuracy of array gain calculation.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A broadband array gain prediction method based on acoustic field spatial correlation correction, the method comprising the following steps:

[0007] Step 1: Obtain the array gain evaluation calculation parameters and marine environmental parameters;

[0008] Step 2: Utilize array gain evaluation calculation parameters and marine environmental parameters to perform broadband acoustic field calculations, obtain the amplitude and phase of signals at different frequencies arriving at the receiving array element positions, and construct the channel frequency response function.

[0009] Step 3: Use the channel frequency response function to estimate the correlation coefficient of the signal received by the array elements after the useful signal is distorted by the channel, and form a signal correlation coefficient matrix between array elements;

[0010] Step 4: Use the isotropic noise field model to estimate the inter-channel noise correlation coefficient after the processing frequency band deviates from the ideal frequency, and form a noise correlation coefficient matrix;

[0011] Step 5: Calculate the receiver array gain using the signal correlation coefficient matrix and the noise correlation coefficient matrix.

[0012] Preferably, the array gain evaluation calculation parameters include array element position, array element number, target position, calculation frequency, and frequency interval.

[0013] Preferably, the broadband sound field calculation employs a sound field modeling method based on ray acoustics.

[0014] Preferably, the element in the i-th row and j-th column of the signal correlation coefficient matrix is ​​represented as:

[0015]

[0016] In the formula, ω1 represents the lower limit of the calculated frequency, ω2 represents the upper limit of the calculated frequency, Re[·] represents the operation of taking the real part, and P i (ω) represents the channel frequency response from the target to the i-th array element, and ω represents the calculation frequency.

[0017] Preferably, the element in the i-th row and j-th column of the noise correlation coefficient matrix is ​​represented as:

[0018]

[0019] In the formula, ω represents the calculated frequency, and a ij Let c represent the distance from the i-th array element to the n-th array element, and let c represent the speed of sound.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This method can effectively reflect the coupling between the underwater acoustic array and the actual marine environment during operation, and can improve the accuracy of array gain calculation results. Attached Figure Description

[0022] Figure 1 This is a flowchart of the method of the present invention.

[0023] Figure 2 This is a schematic diagram of the bilinear interpolation method for ocean depth data.

[0024] Figure 3 This is a schematic diagram of the trilinear interpolation method for sound velocity profile data.

[0025] Figure 4 This is a schematic diagram of the calculation process for the X-ray acoustic field model.

[0026] Figure 5 This is a schematic diagram of the test scenario.

[0027] Figure 6 This is a schematic diagram of the measured sound velocity profile.

[0028] Figure 7 A schematic diagram of the propagation loss modeling results.

[0029] Figure 8 This is a schematic diagram of the signal correlation coefficient matrix obtained using the sound field model.

[0030] Figure 9 This is a schematic diagram of the time-domain received signal.

[0031] Figure 10 This is a time-frequency diagram of the received signal.

[0032] Figure 11 This is a schematic diagram of the correlation coefficient matrix obtained using actual received data. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0034] Reference Figure 1 As shown, a broadband array gain prediction method based on acoustic field spatial correlation correction includes the following 5 steps.

[0035] Step 1: Obtain array gain assessment calculation parameters and marine environmental parameters. The array gain assessment calculation parameters mainly include the number and location of array elements, target location, calculation frequency band, and frequency spacing. The marine environmental parameters include sound velocity profile, sea depth, seabed sediment, and other parameters, which are read from the marine environmental historical database.

[0036] Step 2 involves using array gain evaluation parameters and marine environmental parameters to perform broadband acoustic field calculations, obtaining the amplitude and phase of signals at different frequencies arriving at the receiving array element locations, and then using the calculated amplitude and phase to construct the channel frequency response function. The specific process of this step is as follows:

[0037] (2.1) Input parameter configuration: Configure sound field calculation parameters, input marine environmental parameters (sea depth, sound velocity profile, seabed sediment type and its acoustic parameters corresponding to each distance sampling point in a certain direction) and array gain evaluation calculation parameters.

[0038] (2.2) Preprocessing: initialization of seabed data and initialization of sound velocity profile.

[0039] In this invention, the marine environment database is generally gridded data with a certain resolution. In order to obtain the sea depth and sound speed profile data on the target to the array element measurement line, the read sea depth data and sound speed profile data need to be interpolated.

[0040] For ocean depth data, a bilinear interpolation method is used, such as... Figure 2 As shown, for a point on the survey line, the sea depth f(x, y), where x and y represent spatial coordinates, takes the four nearest measured sea depth data, namely f(x1, y1), f(x1, y2), f(x2, y1), and f(x2, y2), then f(x, y) can be expressed as:

[0041]

[0042] in:

[0043]

[0044] For sound velocity profile data, this invention employs a trilinear interpolation method, such as... Figure 3 As shown, for the sound velocity f(x, y, z) at a point on the survey line, where x, y, z represent spatial coordinates, the eight nearest measured sound velocity data are taken as f(x1, y1, z1), f(x1, y2, z1), f(x2, y1, z1), f(x2, y2, z1), f(x1, y1, z2), f(x1, y2, z2), f(x2, y1, z2), f(x2, y2, z2). Then the sound velocity at this point can be expressed as:

[0045] f(x,y,z)=f(x1,y1,z1)(1-x d (1-y) d (1-z) d )+f(x2, y1, z1)x d (1-y d (1-z) d )+f(x1, y1, z2)(1-x d (1-y) d )z d +f(x2, y1, z2)x d (1-y d )z d +f(x1, y2, z1)(1-x d )y d (1-z d )+f(x2, y2, z1)x d y d(1-z d )+f(x1, y2, z2)(1-x d )y d z d +f(x2, y2, z2)x d y d z d

[0046] in:

[0047] x d = (x-x0) / (x1-x0)

[0048] y d =(y-y0) / (y1-y0)

[0049] z d =(z-z0) / (z1-z0)

[0050] (2.3) Sound field calculation: Broadband sound field calculation is performed using the sound field modeling method of ray acoustics.

[0051] like Figure 4 As shown, in this step, the trajectory, information, and sound pressure of a single ray are first obtained through single-ray tracking. Then, the results of all ray tracking are superimposed to obtain the ray trajectory, intrinsic ray arrival information, and superimposed sound pressure of the sound field over the entire sea area. The intrinsic ray arrival information and the superimposed sound pressure need to be corrected using predetermined loss types. The propagation loss can be obtained using the corrected superimposed sound pressure, and the amplitude and phase of signals arriving at the receiving array element at different frequencies can be calculated using the corrected intrinsic ray arrival information. The use of ray acoustics for sound field modeling in this step is a standard technique in this field and will not be elaborated upon further here.

[0052] (2.4) Output: Calculate and output the channel frequency response function:

[0053]

[0054] Where A i θ represents the amplitude of the received signal at the i-th channel. i This represents the signal phase at the i-th channel, where j is an imaginary number.

[0055] In step 2 of this invention, the combination of marine environmental data and acoustic field modeling methods is used, which is closer to the actual situation and more clearly reflects the impact of the underwater acoustic channel on the target signal, and can more accurately calculate the correlation coefficient of the target signal.

[0056] Step 3: Use the channel frequency response function to estimate the correlation coefficient of the signal received by the array elements after the useful signal is distorted by the channel, and form a signal correlation coefficient matrix.

[0057] (3.1) Construct the receiver array frequency response matrix P(ω)=[P1(ω), P2(ω), ..., P N [(ω)], where P i (ω) represents the channel frequency response from the target to the i-th array element.

[0058] (3.2) Construct the signal correlation coefficient matrix R using the frequency response matrix of the receiver array. s The element in the i-th row and j-th column can be represented as:

[0059]

[0060] In the formula, ω1 represents the lower limit of the calculation frequency, ω2 represents the upper limit of the calculation frequency, Re[·] represents the operation of taking the real part, ω represents the calculation frequency, and t represents the time interval.

[0061] Step 4: Estimate the inter-channel noise correlation coefficients after the processed frequency band deviates from the ideal frequency using an isotropic noise field model, and form the noise correlation coefficient matrix R. n The element in the i-th row and i-th column can be represented as:

[0062]

[0063] In the formula, ω represents the calculated frequency, and d ij Let represent the distance from the i-th array element to the j-th array element, and c represent the speed of sound.

[0064] In step 4 of this invention, an isotropic noise field model is used. Compared with traditional methods, this model can calculate the noise correlation coefficient between channels when the spacing between array elements does not meet half-wavelength, and has a wider range of applications.

[0065] Step 5: Calculate the receiver array gain using the signal correlation coefficient matrix and the noise correlation coefficient matrix.

[0066] According to the definition of correlation coefficient, the signal-to-noise ratio of the array output can be expressed as:

[0067]

[0068] The array gain is defined as the ratio of the output signal-to-noise ratio to the input signal-to-noise ratio in decibels. Therefore, the array gain can be expressed as:

[0069]

[0070] In summary, since the accuracy of receiver array gain calculation is determined by the accuracy of signal gain and noise gain calculation, this invention improves the accuracy of array gain calculation by calculating the signal correlation coefficient matrix and the noise correlation coefficient matrix to obtain the signal gain and noise gain.

[0071] To compare the actual array gain with the calculation results of the method described in this invention, data analysis was performed using sea trial data from a sound field spatial correlation measurement. The test scenario is as follows: Figure 5 As shown, in this experiment, a transmitting array was used as the sound source, and a towed linear array was used for receiving. The distance between the linear array and the sound source was 2.50 km, with an azimuth of 127.971° and a heading of 21.8°. The sea area was approximately 2800 m deep, and the seabed was relatively flat. The measured sound velocity profile is shown below. Figure 6 As shown; during the test, the signal was a linear frequency modulated signal of 1400-1600Hz, the receiving array depth was 145m, and the transmitting array depth was 150m.

[0072] In this experimental scenario, a ray acoustic model was used for sound field modeling, with a calculation frequency band of 1400-1600Hz and a frequency resolution of 10Hz. Typical propagation loss calculation results are as follows: Figure 7 As shown; step 3 is used to calculate the signal correlation coefficient matrix between array elements, and the results are as follows. Figure 8 As shown, fringes generated by signal interference can be observed. The spatial correlation coefficient matrix of the sound field is calculated using actual received data, and the typical time-domain waveform of the received signal is shown below. Figure 9 As shown, a typical received signal time-frequency diagram is as follows: Figure 10 As shown in the figure. At this time, the transmitting array and the receiving array are relatively close, and it is clear that the time-frequency diagram of the useful signal exhibits linear frequency modulation characteristics, with a high signal-to-noise ratio.

[0073] The signal correlation coefficient matrix between array elements is calculated using the method described in step 3, and the results are as follows: Figure 11 As shown in the figure. The diagonal line represents the intrinsic correlation coefficient of the acoustic channel, with a value of 1. Along the diagonal line, a periodic variation in the spatial correlation coefficient is clearly observed, and the fringe distribution is similar to... Figure 8 The simulation results are consistent, but because the actual received signal contains noise components, the correlation coefficient at the dark stripes is higher than the simulation results.

[0074] Step 5 was used to calculate the array gain prediction, and the result was 24.7 dB. The gain was then processed using actual data analysis, and beamforming was applied to the received signal. The time-domain waveform of the processed signal is shown below. Figure 11 As shown, the signal-to-noise ratio before and after beamforming yields an array gain of 25.9 dB. Compared to the actual analysis results, the prediction error of the calculation method described in this invention is approximately 1.4 dB, which is within an acceptable range.

Claims

1. A broadband array gain prediction method based on acoustic field spatial correlation correction, characterized in that, The method includes the following steps: Step 1: Obtain the array gain evaluation calculation parameters and marine environmental parameters; Step 2: Utilize array gain evaluation calculation parameters and marine environmental parameters to perform broadband acoustic field calculations, obtain the amplitude and phase of signals at different frequencies arriving at the receiving array element positions, and construct the channel frequency response function. Step 3: Use the channel frequency response function to estimate the correlation coefficient of the signal received by the array elements after the useful signal is distorted by the channel, and form a signal correlation coefficient matrix between array elements; Step 4: Use the isotropic noise field model to estimate the inter-channel noise correlation coefficient after the processing frequency band deviates from the ideal frequency, and form a noise correlation coefficient matrix; Step 5: Calculate the receiver array gain using the signal correlation coefficient matrix and the noise correlation coefficient matrix; The specific method for step 3 is as follows: The channel frequency response function is expressed as follows: ,in This represents the amplitude of the received signal at the i-th channel. This indicates the signal phase at the i-th channel. It is an imaginary number; Construct the frequency response matrix of the receiver array ,in This represents the channel frequency response from the target to the i-th array element; Construct the signal correlation coefficient matrix R using the frequency response matrix of the receiver array. s The element in the i-th row and j-th column is represented as: In the formula, This indicates the lower limit of the calculated frequency. This indicates the upper limit of the calculated frequency. This indicates the operation of taking the real part. This represents the channel frequency response from the target to the i-th array element. Indicates the calculated frequency. Indicates a time interval; The specific method for step 4 is as follows: The noise correlation coefficients between channels after the processing frequency band deviates from the ideal frequency are estimated using an isotropic noise field model, forming a noise correlation coefficient matrix R. n， The element in the i-th row and j-th column is represented as: In the formula, Indicates the calculated frequency. Indicates the first Each element to the first The distance between each array element, It indicates the speed of sound.

2. The broadband array gain prediction method based on acoustic field spatial correlation correction as described in claim 1, characterized in that, The array gain evaluation calculation parameters include array element position, number of array elements, target position, calculation frequency, and frequency interval.

3. The broadband array gain prediction method based on acoustic field spatial correlation correction as described in claim 1, characterized in that, The broadband sound field calculation employs a sound field modeling method based on ray acoustics.

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