Broadband array gain forecasting method based on sound field spatial correlation correction

Abstract

The invention discloses a broadband array gain forecasting method based on sound field spatial correlation correction. The method comprises the following steps: carrying out sound field modeling by utilizing marine environment data, calculating a channel frequency response function from a target to each array element position, estimating a correlation coefficient of an array element receiving signal after a useful signal is subjected to channel distortion, and forming a signal correlation coefficient matrix; an isotropic noise field model is used for estimating inter-channel noise correlation coefficients after the processing frequency band deviates from the ideal frequency, and a noise correlation coefficient matrix is formed; and finally calculating the array gain by using the two correlation coefficient matrixes. According to the method, the coupling condition of the underwater acoustic array and the actual marine environment in the working process can be effectively reflected, and the accuracy degree of the array gain calculation result can be improved.

Description

Technical Field

[0001] The invention belongs to the field of underwater acoustic signal processing, and in particular relates to a broadband array gain prediction method based on sound field spatial correlation correction. Background Art

[0002] In the field of modern underwater acoustic signal processing, array signal processing technology often plays a vital role. In sonar systems, beamforming technology is often used to improve the signal-to-noise ratio of received signals by utilizing the spatial correlation of array received signals. In the process of underwater target detection, it is necessary to master the detection efficiency of the sonar system in the actual environment based on the accurate calculation of array gain, which is of great significance for the combined use of techniques and tactics.

[0003] Array gain estimation is an important part of sonar equipment decision-making assistance technology. In the process of conventional sonar signal processing, the ocean waveguide environment is often regarded as an isotropic uniform environment, and the array spacing meets the half-wavelength condition, that is, the received target signal is completely correlated and the background noise is completely uncorrelated; but the actual ocean environment is affected by internal waves, wind and waves, surface ships and other factors, and the underwater acoustic channel shows time-varying and space-varying characteristics, resulting in reduced signal time-space correlation. In sonar systems, beamforming technology is often used. This technology uses the spatial correlation of the received signal of the array to improve the signal-to-noise ratio of the received signal. However, as the sonar frequency decreases and the array element spacing increases, the signal correlation between the array elements decreases, the array processing gain deviates from the theoretical value, and the accuracy of the sonar detection effectiveness evaluation is reduced. Therefore, it is of great significance to study the impact of the acoustic field time-space correlation on the sonar system time-space processing gain and improve the accuracy of the detection effectiveness evaluation. Summary of the invention

[0004] The purpose of the present invention is to provide a broadband array gain prediction method based on sound field spatial correlation correction to solve the problem in the background technology that the working environment of the underwater acoustic array is inconsistent with the ideal environment, resulting in reduced accuracy in array gain calculation.

[0005] To achieve the above object, the present invention provides the following technical solutions:

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

[0007] Step 1, obtaining array gain evaluation calculation parameters and ocean environment parameters;

[0008] Step 2: Calculate the broadband sound field using the array gain evaluation calculation parameters and the ocean environment parameters to obtain the amplitude and phase of different frequency signals arriving at the receiving array element position, so as to construct a channel frequency response function;

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

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

[0011] Step 5: Calculate the receiving 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 adopts a sound field modeling method of ray acoustics.

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

[0015] In the formula, ω1 represents the lower limit of the calculation frequency, ω2 represents the upper limit of the calculation frequency, Re[·] represents the real part operation, and P i (ω) represents the channel frequency response from the target to the i-th array element, and ω represents the calculation frequency.

[0016] Preferably, the element in the i-th row and j-th column of the noise correlation coefficient matrix is ​​expressed as:

[0017]

[0018] In the formula, ω represents the calculation frequency, a ij represents the distance from the ith array element to the jth array element, and c represents the speed of sound.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This method can effectively reflect the coupling situation between the underwater acoustic array and the actual ocean environment during its operation, and can improve the accuracy of the array gain calculation results. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Flow chart of the method of the present invention.

[0022] Figure 2 A schematic diagram of the bilinear interpolation method for ocean depth data.

[0023] Figure 3 Schematic diagram of the trilinear interpolation method for sound velocity profile data.

[0024] Figure 4Schematic diagram of the calculation process of the ray acoustics sound field model.

[0025] Figure 5 Schematic diagram of the test scene.

[0026] Figure 6 Schematic diagram of the measured sound velocity profile.

[0027] Figure 7 Schematic diagram of the results of modeling propagation loss.

[0028] Figure 8 Schematic diagram of the signal correlation coefficient matrix obtained using the sound field model.

[0029] Fig. 9 Schematic diagram of received signal in time domain.

[0030] Fig.10 This is a time-frequency diagram of the received signal.

[0031] Fig.11 This is a schematic diagram of the correlation coefficient matrix obtained using actual received data. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the protection scope of the present invention.

[0033] Reference Figure 1 As shown, a broadband array gain prediction method based on sound field spatial correlation correction includes the following five steps.

[0034] Step 1, obtain array gain evaluation calculation parameters and ocean environment parameters; the array gain evaluation calculation parameters mainly include the number and position of array elements, target position, calculation frequency band, and frequency interval; the ocean environment parameters include sound velocity profile, sea depth, bottom quality and other parameters, which are read from the ocean environment history database.

[0035] Step 2: Use the array gain evaluation calculation parameters and ocean environment parameters to perform broadband sound field calculations to obtain the amplitude and phase of different frequency signals arriving at the receiving array element position, and use the calculated amplitude and phase to construct the channel frequency response function. The specific process of this step is as follows:

[0036] (2.1) Input parameter configuration: Configure the acoustic field calculation parameters, input the ocean environment parameters (sea depth, sound velocity profile, seabed bottom type and its acoustic parameters corresponding to each distance sampling point in a certain direction) and array gain evaluation calculation parameters.

[0037] (2.2) Preprocessing: seabed data initialization, sound velocity profile initialization.

[0038] In the present invention, the marine environment database is generally grid data with a certain resolution. In order to obtain the sea depth and sound speed profile data on the target to the array element survey line, the read sea depth data and sound speed profile data need to be interpolated.

[0039] The bilinear interpolation method is used for the sea depth data, such as Figure 2 As shown in the figure, for the sea depth f(x, y) of a point on the survey line, where x and y represent the spatial position coordinates, the four nearest measured sea depth data are taken, namely f(x1, y1), f(x1, y2), f(x2, y1), and f(x2, y2), then f(x, y) can be expressed as:

[0040]

[0041] in:

[0042]

[0043]

[0044] For the sound velocity profile data, the present invention adopts a trilinear interpolation method, such as Figure 3 As shown in the figure, for the sound velocity f(x, y, z) of a point on the survey line, where x, y, z represent the spatial position coordinates, the 8 nearest measured sound velocity data are taken, namely 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 the 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 ) d +f(x2,y1,z2)x d (1-y d ) 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: The sound field modeling method of ray acoustics is used to perform broadband sound field calculation.

[0051] like Figure 4 As shown, in this step, a single sound line trajectory, sound line information and sound pressure are first obtained through single sound line tracking, and then a loop operation is performed to superimpose all sound line tracking results to obtain the whole sea area sound line trajectory, intrinsic sound line arrival information, and sound field superposition sound pressure, wherein the intrinsic sound line arrival information and sound field superposition sound pressure need to be corrected by the set loss type, etc. The propagation loss can be obtained by using the corrected sound field superposition sound pressure, and the amplitude and phase of different frequency signals arriving at the receiving array element position can be calculated by using the corrected intrinsic sound line arrival information. In this step, how to use ray acoustics to model the sound field is a conventional technical means in this field, and will not be described in detail here.

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

[0053]

[0054] Among them A i represents the received signal amplitude at the i-th channel, θ i Represents the signal phase at the i-th channel, and j is an imaginary number.

[0055] In step 2 of the present invention, the combination of ocean environment data and the sound field modeling method is adopted, which is closer to the actual situation, more clearly reflects the influence of the underwater acoustic channel on the target signal, and can more accurately calculate the target signal correlation coefficient.

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

[0057] (3.1) Construct the receiving 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) Use the receiving array frequency response matrix to construct the signal correlation coefficient matrix R s , where the element in the i-th row and j-th column can be expressed as:

[0059]

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

[0061] 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 the noise correlation coefficient matrix R n , where the element in the i-th row and j-th column can be expressed as:

[0062]

[0063] Where ω represents the calculation frequency, d ij represents the distance from the ith array element to the jth array element, and c represents the speed of sound.

[0064] In step 4 of the present invention, an isotropic noise field model is used. Compared with the traditional method, it is able to calculate the noise correlation coefficient between channels when the array element spacing does not meet the half wavelength, and has a wider scope of application.

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

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

[0067]

[0068] The array gain is defined as the decibel ratio of the output signal-to-noise ratio to the input signal-to-noise ratio, so the array gain can be expressed as:

[0069]

[0070] In summary, since the calculation accuracy of the receiving array gain is determined by the calculation accuracy of the signal gain and the noise gain, the present invention obtains the signal gain and the noise gain by calculating the signal correlation coefficient matrix and the noise correlation coefficient matrix, thereby improving the calculation accuracy of the array gain.

[0071] In order to compare the actual array gain with the calculation result of the method described in the present invention, the data of a certain sound field spatial correlation measurement offshore test were used for data analysis. The test scene is as follows: Figure 5 As shown in the figure, in this test, a transmitting array is used as the sound source, and a towed linear array is used for receiving; the linear array is 2.50km away from the sound source, the azimuth is 127.971°, and the heading is 21.8. The sea depth in this sea area is about 2800m, and the seabed is relatively flat. The measured sound velocity profile is as follows Figure 6 As shown; during the test, the signal form is a linear frequency modulation signal of 1400-1600Hz, the receiving array depth is 145m, and the transmitting array depth is 150m.

[0072] In this test scenario, the sound field model is modeled using the sound line acoustic model. The calculation frequency band is 1400-1600Hz, the frequency resolution is 10Hz, and the 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 result is as follows Figure 8 As shown in the figure, the fringes generated by signal interference can be observed. The actual received data is used to calculate the acoustic field spatial correlation coefficient matrix. The typical received signal time domain waveform is shown in Fig. 9 As shown, the typical received signal time-frequency diagram is as follows Fig.10 At this time, the distance between the transmitting array and the receiving array is relatively close, and it can be clearly observed that the useful signal time-frequency diagram has a linear frequency modulation characteristic, and the signal-to-noise ratio is relatively high.

[0073] The signal correlation coefficient matrix between array elements is calculated using the method described in step 3. The result is as follows: Fig.11 The diagonal line in the figure is the sound channel self-correlation coefficient, which is 1. Parallel to the diagonal line, it can be clearly observed that the spatial correlation coefficient changes periodically, and the distribution of stripes is similar to Figure 8 However, since the actual received signal contains noise components, the correlation coefficient at the dark fringes is higher than the simulation result.

[0074] The array gain prediction calculation is performed using step 5, and the result is 24.7 dB. The processing gain is analyzed using actual data, and the received signal is beamformed. The time domain waveform of the processing result is as follows: Fig.11 As shown, the array gain can be obtained by analyzing the signal-to-noise ratio before and after beamforming to be 25.9 dB. Compared with the actual analysis result, the prediction error of the calculation method of the present invention is about 1.4 dB, which is within an acceptable range.

Claims

1. A broadband array gain prediction method based on sound field spatial correlation correction, characterized in that: The method comprises the following steps: Step 1, obtaining array gain evaluation calculation parameters and ocean environment parameters; Step 2: Calculate the broadband sound field using the array gain evaluation calculation parameters and the ocean environment parameters to obtain the amplitude and phase of different frequency signals arriving at the receiving array element position, so as to construct a channel frequency response function; Step 3, using the channel frequency response function to estimate the correlation coefficient of the array element receiving signal after the useful signal is distorted by the channel, to form a signal correlation coefficient matrix between the array elements; Step 4, using an isotropic noise field model to estimate the inter-channel noise correlation coefficient after the processing frequency band deviates from the ideal frequency, and forming a noise correlation coefficient matrix; Step 5: Calculate the receiving array gain using the signal correlation coefficient matrix and the noise correlation coefficient matrix.

2. A broadband array gain prediction method based on sound field spatial correlation correction as claimed in claim 1, characterized in that: The array gain evaluation calculation parameters include array element position, array element quantity, target position, calculation frequency, and frequency interval.

3. The broadband array gain prediction method based on sound field spatial correlation correction according to claim 1, characterized in that: The broadband sound field calculation adopts the sound field modeling method of ray acoustics.

4. The broadband array gain prediction method based on sound field spatial correlation correction according to claim 1, characterized in that: The element in the i-th row and j-th column of the signal correlation coefficient matrix is ​​expressed as: In the formula, ω1 represents the lower limit of the calculation frequency, ω2 represents the upper limit of the calculation frequency, Re[·] represents the real part operation, and P i (ω) represents the channel frequency response from the target to the i-th array element, and ω represents the calculation frequency.

5. The broadband array gain prediction method based on sound field spatial correlation correction according to claim 1, characterized in that: The element in the ith row and jth column of the noise correlation coefficient matrix is ​​expressed as: In the formula, ω represents the calculation frequency, d ij represents the distance from the ith array element to the ith array element, and c represents the speed of sound.

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