Tugboat multipath interference suppression method based on successive variational mode decomposition and cross entropy

Abstract

The present invention discloses a method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy. The method comprises: first, in a period when no transmission signal is received, broadband beamforming is performed on the towed array sonar receiving waveform to estimate the tugboat multipath interference azimuth, a tugboat interference reference waveform corresponding to the interference azimuth is obtained, and an interference azimuth interval corresponding to each tugboat interference path is set; then, in a period when the transmission signal is received, the waveform to be decomposed corresponding to each tugboat interference path is obtained, and within the interference azimuth interval, the waveform to be decomposed is subjected to successive variational mode decomposition in combination with the tugboat interference reference waveform, and the interference waveform is reconstructed by selecting effective modes through power spectrum cross entropy to achieve tugboat interference suppression; the waveform to be decomposed corresponding to the remaining tugboat interference paths is traversed and processed, and finally the tugboat interference suppression on all paths is completed. The present invention effectively improves the zero-pitching problem of the IBF method, and achieves the retention of reverberation while suppressing tugboat multipath interference.

Description

Technical Field

[0001] The present invention relates to a tugboat interference suppression method in the technical field of underwater acoustic signal processing, and in particular to a tugboat multipath interference suppression method based on successive variational mode decomposition and cross entropy. Background Art

[0002] The horizontal receiving array sonar system towed by a tugboat is an important tool in the current field of underwater acoustic signal processing. Due to its simple structure and variable depth, it is widely used in the collection and processing of various types of underwater acoustic signals. Although the towed array is located hundreds to thousands of meters behind the tugboat platform, the self-noise of the tugboat during navigation is still a strong interference, such as Figure 2 As shown. And because the tugboat interference has the characteristics of multipath propagation in the ocean waveguide, there are not only direct waves, but also seabed reflection waves and sea surface reflection waves. The tugboat multipath interference is manifested in the azimuth-time diagram as strong interference in the near end-fire azimuth and weak interference in the away end-fire azimuth, which seriously affects the detection, positioning and imaging performance of the towed array.

[0003] Existing tugboat interference array element domain cancellation methods, such as the inverse beam forming (IBF) method, can effectively suppress tugboat interference, and have the advantages of not being limited by frequency band and suppressing the main lobe and side lobes at the same time. However, when the tugboat interference and the transmitted signal are aliased, the null generated by the IBF method will suppress the reverberation used for seabed imaging in that direction while suppressing the tugboat interference, resulting in the loss of reverberation information in that direction. Existing improved methods based on IBF usually use empirical mode decomposition (EMD). Although EMD can realize adaptive decomposition of modes, it does not have a rigorous mathematical derivation and is greatly affected by noise. It is easy to cause mode aliasing or over-decomposition problems, affecting the effectiveness of tugboat interference suppression. Summary of the invention

[0004] In view of the problems existing in the background technology, the present invention provides a method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy. The method uses successive variational mode decomposition of the beam output waveform of the tugboat interference azimuth, calculates the power spectrum cross entropy of the intrinsic mode (IMF) obtained after decomposition and the reference waveform, selects the mode that meets the judgment criterion to re-synthesize the tugboat interference time domain waveform, and reconstructs the tugboat interference waveform of each array element in the array element domain, thereby realizing array element domain interference cancellation. The present invention effectively solves the problem that when there is aliasing of multipath propagated tugboat interference and reverberation in the acoustic remote sensing imaging scenario, while suppressing the multipath tugboat interference, a zero pit will be formed in the interference azimuth, thereby causing the reverberation in this azimuth to be suppressed at the same time, and has a strong engineering application value in actual underwater acoustic signal processing.

[0005] The technical solution of the present invention is as follows:

[0006] 1. A method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy

[0007] S1: When no transmission signal is received, the towed array sonar receiving waveform is subjected to broadband beamforming, and the interference azimuth corresponding to each tugboat interference path is estimated respectively, so as to obtain the tugboat multipath interference azimuth, and then the interference azimuth interval corresponding to each tugboat interference path and the tugboat interference reference waveform are generated;

[0008] S2: When receiving the transmission signal, the waveform to be decomposed corresponding to each tugboat interference path is obtained; in the interference azimuth interval corresponding to the current tugboat interference path, the tugboat interference reference waveform is combined, and the tugboat interference suppression is performed on the towed array sonar receiving waveform by using the successive variational mode decomposition and power spectrum cross entropy judgment method;

[0009] S3: Repeat S2, traverse and process the waveforms to be decomposed corresponding to the remaining tugboat interference paths obtained during the period of receiving the transmission signal, and complete the tugboat interference suppression on all tugboat interference paths.

[0010] In S1, for each tugboat interference path, the interference azimuth θ of the current tugboat interference path is combined p , the towing distance and depth of the towed array and the interference azimuth interval corresponding to the sea depth setting [θ p - Δθ,θ p +Δθ], Δθ is the interference deviation angle.

[0011] In the different tugboat interference paths, the interference deviation angle of the tugboat interference direct wave path is greater than the interference deviation angle of the tugboat interference seabed reflection path and the seabed-sea surface reflection path.

[0012] In S1, for each tugboat interference path, the interference azimuth θ aligned with the current tugboat interference path is p After beam output, the corresponding tugboat interference frequency domain waveform is obtained, and then the tugboat interference frequency domain waveform is inverse Fourier transformed to obtain the tugboat interference reference waveform i''(t) corresponding to the current tugboat interference path.

[0013] The S2 is specifically:

[0014] S2.1: When receiving the transmission signal, align the current towed array sonar receiving waveform with the current interference azimuth of each towing ship interference path as a beam output to obtain the waveform to be decomposed; then perform successive variational mode decomposition on the current waveform to be decomposed to obtain multiple eigenmodes;

[0015] S2.2: Calculate the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current interference path, select the eigenmode according to the power spectrum cross entropy and reconstruct the tugboat interference time domain waveform;

[0016] S2.3: After reconstructing the waveform of each array element of the reconstructed tugboat interference time domain waveform in the array element domain, a reconstructed tugboat interference waveform is obtained, and the current towed array sonar receiving waveform and the reconstructed tugboat interference waveform are offset in the array element domain to obtain an updated towed array sonar receiving waveform;

[0017] S2.4: Obtain a new interference azimuth angle after searching through broadband beamforming within the interference azimuth interval of the current tugboat interference path, repeat S2.1-S2.3, perform array element domain cancellation on the towed array sonar receiving waveform of the current tugboat interference path, traverse and search for the azimuth angle within the interference azimuth interval of the current tugboat interference path and process it until no tugboat interference is detected within the interference azimuth interval of the current tugboat interference path, thereby achieving tugboat interference suppression.

[0018] In S2.2, the calculation formula of the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current tugboat interference path is as follows:

[0019] H=-Σ Nh n=Nl P u (f n )log(P i (f n ))

[0020] Where H is the power spectrum cross entropy of each eigenmode, P u (f n ) is each eigenmode u(t) at frequency f n The normalized power spectrum of the corresponding frequency point, P i (f n ) is the tugboat interference reference waveform i''(t) at frequency f n Normalized power spectrum of the corresponding frequency point; Nl is the lower limit frequency f of the Fourier transform of the towed array sonar receiving waveform l The corresponding frequency index value, Nh is the upper limit frequency f after Fourier transform of the towed array sonar receiving waveform h The corresponding frequency index value, n is the frequency index value.

[0021] In 2.2, the eigenmode is selected according to the power spectrum cross entropy and the tugboat interference time domain waveform is reconstructed, specifically:

[0022] The power spectrum cross entropy is less than or equal to the preset entropy value H T After adding the eigenmodes in the time domain, the reconstructed tugboat interference time domain waveform i is obtained. new (t), the formula is as follows:

[0023] i new (t)=Σ Kk =1 u k (t)

[0024] Among them, K is less than or equal to the preset entropy value H T The number of eigenmodes, u k (t) is the eigenmode that meets the power spectrum cross entropy decision criterion.

[0025] In 2.3, after the reconstructed tugboat interference time domain waveform is reconstructed on the array element domain, the reconstructed tugboat interference waveform x is obtained. tow (t), the reconstruction formula is as follows:

[0026] x tow (t)=IFFT[i new (t)exp(-j2πf(m-1)d cosθ p / c)],m=1,2,…M

[0027] Where IFFT[ ] represents inverse Fourier transform, i new (t) represents the reconstructed tugboat interference time domain waveform, f represents the frequency, m represents the array element number of the towed array, d represents the array element spacing, θ p represents the interference azimuth of the current towing ship interference path, c represents the speed of sound in water, and M represents the number of towline array elements.

[0028] 2. A computer device

[0029] The device includes a memory and a processor, wherein the memory stores a computer program, and when the processor executes the computer program, the steps of the method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy are implemented.

[0030] 3. A computer-readable storage medium

[0031] The medium stores a computer program, and when the computer program is executed by the processor, the steps of the method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy are implemented.

[0032] The beneficial effects of the present invention are:

[0033] The present invention introduces successive variational mode decomposition into interference decomposition, takes power spectrum cross entropy as the decision criterion for selecting effective modes, and reconstructs the waveform of the tugboat interference array element domain. This effectively solves the problem that when there is aliasing between the multipath propagated tugboat interference and reverberation in the acoustic remote sensing imaging scenario, a null sink will be formed in the interference azimuth while suppressing the multipath tugboat interference, thereby causing the reverberation in the azimuth to be suppressed at the same time. That is, the null sink problem of the IBF method is effectively improved, and the reverberation is retained while the tugboat multipath interference is suppressed. This method has a strong engineering application value in actual underwater acoustic signal processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the method of the present invention.

[0035] Figure 2 This is a schematic diagram of multipath propagation of tugboat interference in ocean waveguide.

[0036] Figure 3 is a azimuth-time diagram for periods when no transmitted signals are received.

[0037] Figure 4 It is the SVMD decomposition result of the beam output of the tugboat interference direct wave azimuth (157.5° azimuth), where (a) is the eigenmodes 1-4 obtained by modal decomposition, and (b) is the eigenmodes 5-8 obtained by modal decomposition.

[0038] Figure 5 It is the eigenmodes 9-13 in the SVMD decomposition result of the beam output of the tugboat interference direct wave azimuth (157.5° azimuth).

[0039] Figure 6 is the azimuth-time diagram of conventional beamforming.

[0040] Figure 7 It is the azimuth-time diagram after tugboat interference suppression by broadband inverse beamforming.

[0041] Figure 8 It is a azimuth-time diagram after the tugboat interference is suppressed by the method of the present invention.

[0042] Fig. 9 This is the time slice diagram of conventional beamforming at t=5.286s.

[0043] Fig.10 It is the time slice diagram after broadband inverse beamforming is used to suppress tugboat interference at t=5.286s.

[0044] Fig.11 It is a time slice diagram after the tugboat interference suppression is performed by the method of the present invention at t=5.286s. DETAILED DESCRIPTION

[0045] The present invention is further described using the towed array data from an imaging experiment in a certain year. In this embodiment, the number of array elements of the towed array is 96, the array element spacing is 0.417 meters, the sampling frequency is 16kHz, and the transmitted signal is a linear frequency modulation signal with a pulse width of 1s and a frequency band range of 1.7k-1.9kHz. The frequency point interval is 0.1Hz, and the array element spacing is 0.417m. The search azimuth is [0°, 180°], and the speed of sound in water is 1500m. The flow chart of the method proposed by the present invention is as follows: Figure 1 As shown, the specific steps are as follows:

[0046] S1: During the period when no transmission signal is received, the towed array sonar receiving waveform is subjected to broadband beamforming, and the interference azimuth corresponding to each tugboat interference path is estimated respectively, so as to obtain the tugboat multipath interference azimuth, and then the interference azimuth interval and tugboat interference reference waveform corresponding to each tugboat interference path are generated; in this embodiment, the frequency point interval is 0.1Hz, and the array element spacing is 0.417m. Search azimuth [0°, 180°], the speed of sound in water is 1500m. During the period when no transmission signal is received, the towed array sonar receiving waveform x'(t) contains only tugboat interference and noise, and the formula is as follows:

[0047] x'(t) =i'(t) +n'(t)

[0048] Wherein, i'(t) is the tugboat interference during the period when the transmission signal is not received, and n'(t) is the noise during the period when the transmission signal is not received.

[0049] For each tugboat interference path, combined with the interference azimuth θ of the current tugboat interference path p , the towing distance and depth of the towed array and the sea depth (i.e., prior information) to set the corresponding interference azimuth interval [θ p - Δθ,θ p +Δθ], Δθ is the interference deviation angle. The interference azimuth angle θ in the interference azimuth interval p is the direction where the beam output power is maximum.

[0050] Among different tugboat interference paths, the interference deviation angle of the tugboat interference direct wave path is greater than the interference deviation angle of the tugboat interference seabed reflection path and the seabed-sea surface reflection path, and the interference deviation angle of the tugboat interference seabed reflection path and the seabed-sea surface reflection path are the same.

[0051] Specifically:

[0052] In this embodiment, there are three multipath interference azimuths [θ1, θ2, θ3]. The first interference azimuth θ1 is 157.5°, corresponding to the tugboat interference direct wave path; the second interference azimuth θ2 is 109°, and the third interference azimuth θ3 is 90.5°, both corresponding to the tugboat interference reflected wave path. The towing depth is about 50m, the towing distance is about 800m, and the sea depth is about 1100m. The azimuth-time diagram of the period when the transmission signal is not received is as follows: Figure 3 shown.

[0053] For the direct wave path of the tugboat interference, its azimuth angle θ p It is mainly affected by the towing depth and towing distance of the towed array. The towing depth and towing distance change little during the tugboat’s voyage, so the azimuth angle remains basically unchanged. Considering the beam broadening phenomenon in the azimuth of the direct wave, the interference azimuth interval is set to [θ p -5°,θ p +5°].

[0054] For the tugboat interference seabed reflection path and seabed-sea surface reflection path, its azimuth angle θ p It is mainly affected by the towing depth, towing distance and sea depth. The towing depth and towing distance change little during the tugboat’s voyage, but the sea depth will change as the tugboat sails, which will cause the azimuth to change. Therefore, the interference azimuth interval is set to [θ p -2°,θ p +2°].

[0055] For each tugboat interference path, the interference azimuth θ aligned with the current tugboat interference path p After beam output, the corresponding tugboat interference frequency domain waveform is obtained, and then the tugboat interference frequency domain waveform is inverse Fourier transformed to obtain the tugboat interference reference waveform i''(t) corresponding to the current tugboat interference path.

[0056] S2: During the period of receiving the transmission signal, the waveform to be decomposed corresponding to each tugboat interference path is obtained; within the interference azimuth interval corresponding to the current tugboat interference path, the tugboat interference reference waveform is combined, and the tugboat interference suppression is performed on the towed array sonar receiving waveform using the successive variational mode decomposition and power spectrum cross entropy judgment method; during the period of receiving the transmission signal, the towed array sonar receiving waveform x(t) satisfies the following formula:

[0057] x(t)=s(t)+i(t)+n(t)

[0058] Where s(t) is the signal received by the array, i(t) is the tugboat interference during the period of receiving the transmission signal, and n(t) is the noise during the period of receiving the transmission signal.

[0059] S2 is specifically:

[0060] S2.1: During the period of receiving the transmission signal, the current towed array sonar receiving waveform is aligned with the current interference azimuth of each tugboat interference path as a beam output to obtain a waveform to be decomposed; and then the current waveform to be decomposed is subjected to successive variational mode decomposition (SVMD) to obtain multiple eigenmodes; in this embodiment, the SVMD decomposition result of the waveform to be decomposed outputted at the azimuth θ1 of the tugboat interference direct wave is as follows: Figure 4 (a) Figure 4 (b) and Figure 5 shown.

[0061] S2.2: Calculate the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current interference path, select the eigenmode according to the power spectrum cross entropy and reconstruct the tugboat interference time domain waveform;

[0062] The calculation formula of the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current interference path is as follows:

[0063] H=-Σ Nh n=Nl P u (f n )log(P i (f n ))

[0064] Where H is the power spectrum cross entropy of each eigenmode, P u (f n ) is each eigenmode u(t) at frequency f n The normalized power spectrum of the corresponding frequency point, P i (f n ) is the tugboat interference reference waveform i''(t) at frequency f n Normalized power spectrum of the corresponding frequency point; Nl is the lower limit frequency f of the Fourier transform of the towed array sonar receiving waveform l The corresponding frequency index value, Nh is the upper limit frequency f after Fourier transform of the towed array sonar receiving waveform h The corresponding frequency index value, n is the frequency index value.

[0065] According to the power spectrum cross entropy, the eigenmode is selected and the time domain waveform of the tugboat interference is reconstructed, which is as follows:

[0066] The power spectrum cross entropy is less than or equal to the preset entropy value H T After adding the eigenmodes in the time domain, the reconstructed tugboat interference time domain waveform i is obtained. new (t), the formula is as follows:

[0067] i new (t)=Σ K k =1 uk (t)

[0068] Among them, K is less than or equal to the preset entropy value H T The number of eigenmodes, u k (t) is the eigenmode that meets the power spectrum cross entropy judgment criterion, that is, the power spectrum cross entropy is less than or equal to the preset entropy value H T The eigenmode of .

[0069] In this embodiment, the cross entropy threshold is set to H T =9, and the azimuth of the direct wave of the tugboat interference is taken as an example for explanation. The results of solving the power spectrum cross entropy of the 13 eigenmodes corresponding to the azimuth of the direct wave of the tugboat interference θ1 and the interference reference waveform are shown in Table 1. Among the 13 eigenmodes, the 8th and 9th eigenmodes meet the judgment criteria, and the 8th and 9th eigenmodes are added to reconstruct the tugboat interference time domain waveform of this azimuth.

[0070] Table 1 shows the power spectrum cross entropy results corresponding to the 13 eigenmodes under the azimuth θ1 of the direct wave of the tugboat interference

[0071]

[0072] S2.3: After reconstructing the waveform of each element in the array element domain, the reconstructed tugboat interference waveform is obtained. The current towed array sonar receiving waveform and the reconstructed tugboat interference waveform are offset in the array element domain to obtain the updated towed array sonar receiving waveform. The formula is x(t)=x(t)-x tow (t), the towed array sonar receiving waveform x(t) is updated at each array element domain cancellation, and the updated towed array sonar receiving waveform x(t) is used as the input value for the next round of array element domain cancellation iteration;

[0073] Among them, after the reconstructed tugboat interference time domain waveform is reconstructed on the array element domain, the reconstructed tugboat interference waveform x is obtained. tow (t), the reconstruction formula is as follows:

[0074] x tow (t)=IFFT[i new (t)exp(-j2πf(m-1)d cosθ p / c)],m=1,2,…M

[0075] Where IFFT[ ] represents inverse Fourier transform, i new (t) represents the reconstructed tugboat interference time domain waveform, f represents the frequency, m represents the array element number of the towed array, d represents the array element spacing, θ p represents the interference azimuth of the current interference path, c represents the speed of sound in water, and M represents the number of towed array elements.

[0076] S2.4: Obtain a new interference azimuth angle after searching through broadband beamforming within the interference azimuth interval of the current tugboat interference path, repeat S2.1-S2.3, perform array element domain cancellation on the towed array sonar receiving waveform of the current tugboat interference path, traverse and search for the azimuth angle within the interference azimuth interval of the current tugboat interference path and process it until no tugboat interference is detected within the interference azimuth interval of the current tugboat interference path, thereby achieving tugboat interference suppression.

[0077] S3: Repeat S2, traverse and process the waveforms to be decomposed corresponding to the remaining tugboat interference paths obtained during the period of receiving the transmission signal, and complete the tugboat interference suppression on all tugboat interference paths.

[0078] The results of solving the power spectrum cross entropy of the eigenmodes corresponding to the second interference azimuth angle θ2 and the third interference azimuth angle θ3 and the interference reference waveform are shown in Table 2 and Table 3 respectively. Among the eigenmodes obtained at the second interference azimuth angle θ2, the eigenmode No. 6 meets the judgment criteria, and the eigenmode No. 6 is used as the interference time domain waveform of the tugboat at this azimuth; among the eigenmodes obtained at the third interference azimuth angle θ3, the eigenmode No. 7 meets the judgment criteria, and the eigenmode No. 7 is used as the interference time domain waveform of the tugboat at this azimuth.

[0079] Table 2 shows the power spectrum cross entropy results corresponding to the six eigenmodes at 109°.

[0080]

[0081] Table 3 shows the power spectrum cross entropy results corresponding to the 7 eigenmodes at 90.5°.

[0082]

[0083] Figure 6 , Figure 7 and Figure 8 They are the azimuth-time diagrams comparing various tugboat multipath interference suppression methods. During this period, the tugboat multipath interference overlaps with the reverberation in three azimuths.

[0084] Figure 6 This is the azimuth-time diagram of conventional beamforming. It can be seen that there is direct wave path tugboat interference at 157.5° azimuth, and there is obvious beam broadening due to near-field multipath transmission. There is reflected path tugboat interference at 109° and 90.5° azimuths. In the figure, 1.6s-2.6s is the arrival time of the transmitted signal. In the period of 2.5s-6.5s, there is reverberation generated by the scattering of the transmitted signal on the seabed. The tugboat multipath interference overlaps with the reverberation at 157.5°, 109° and 90.5° azimuths.

[0085] Figure 7It is the azimuth-time diagram after broadband inverse beamforming is used to suppress tugboat interference. Broadband inverse beamforming is used to suppress tugboat multipath interference. The tugboat interference is suppressed at the azimuth of 157.5°, and the phenomenon of interference beam broadening is also suppressed, but the reverberation at this azimuth is also suppressed. The extremely strong interference suppression capability suppresses the transmission signal in the period of 1.6s-2.6s. The tugboat interference is suppressed at the azimuths of 109° and 90.5°, but the reverberation and transmission signal at this azimuth are also suppressed.

[0086] Figure 8 It is an azimuth-time diagram after tugboat interference suppression by the method of the present invention. By using the method of the present invention to suppress tugboat interference, tugboat interference is suppressed at 157.5°, 109° and 90.5° azimuths, the beam broadening phenomenon of interference at 157.5° azimuth is suppressed, and the amplitude of suppression of transmission signal and reverberation is greatly reduced.

[0087] Fig. 9 , Fig.10 and Fig.11 They are time slice diagrams for comparing tugboat multipath interference suppression methods at t=5.286s, when the reverberation generated by the transmitted signal and the tugboat multipath interference are overlapped in the multipath interference direction.

[0088] Fig. 9 This is the time slice diagram at t=5.286s after conventional beamforming. The amplitude at 157.5° azimuth is -24.94dB, the amplitude at 109° azimuth is -29.52dB, and the amplitude at 90.5° azimuth is -35.06dB.

[0089] Fig.10 This is the time slice diagram at t=5.286s after broadband inverse beamforming is used for suppression. The amplitude at the azimuth of 157.5° is -54.18dB, which is suppressed by 29.24dB; the amplitude at the azimuth of 109° is -41.32dB, which is suppressed by 11.80dB; the amplitude at the azimuth of 90.5° is -41.92dB, which is suppressed by 6.86dB. Broadband inverse beamforming greatly suppresses the tugboat interference, forms a null in the interference azimuth and suppresses the reverberation, resulting in the loss of effective information.

[0090] Fig.11This is a time slice diagram at t=5.286s after suppression using the method of the present invention. The amplitude at the azimuth of 157.5° is -29.69dB, which is suppressed by 4.75dB; the amplitude at the azimuth of 109° is -33.29dB, which is suppressed by 3.77dB; the amplitude at the azimuth of 90.5° is -36.69dB, which is suppressed by 1.63dB. The method of the present invention effectively suppresses the tugboat multipath interference, improves the zero-pitching problem of broadband inverse beamforming, and retains the reverberation as much as possible in the interference azimuth, with an effect better than broadband inverse beamforming.

[0091] In summary, the method of the present invention performs successive variational mode decomposition and tugboat interference reconstruction on the tugboat interference signal, can effectively suppress the tugboat multipath interference through array element domain cancellation, improve the nulling problem of broadband inverse beamforming, and retain the reverberation in the interference direction as much as possible while suppressing the tugboat multipath interference. The performance is better than that of the broadband inverse beamforming method.

[0092] The present invention provides a computer device, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of the method when executing the computer program.

[0093] The present invention provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the method are implemented.

[0094] The present invention proposes a computer program product, comprising a computer program / instructions, which implement the steps of the method when executed by a processor.

[0095] Finally, it should be noted that the above embodiments and explanations are only used to illustrate the technical solution of the present invention rather than to limit it. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope disclosed in the technical solution of the present invention, which should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy, characterized in that: The following steps are involved: S1: When no transmission signal is received, the towed array sonar receiving waveform is subjected to broadband beamforming, and the interference azimuth corresponding to each tugboat interference path is estimated respectively, so as to obtain the tugboat multipath interference azimuth, and then the interference azimuth interval corresponding to each tugboat interference path and the tugboat interference reference waveform are generated; S2: When receiving the transmission signal, the waveform to be decomposed corresponding to each tugboat interference path is obtained; In the interference azimuth interval corresponding to the current tugboat interference path, combined with the tugboat interference reference waveform, the tugboat interference suppression is performed on the towed array sonar receiving waveform using the successive variational mode decomposition and power spectrum cross entropy judgment method. S3: Repeat S2, traverse and process the waveforms to be decomposed corresponding to the remaining tugboat interference paths obtained during the period of receiving the transmission signal, and complete the tugboat interference suppression on all tugboat interference paths.

2. According to claim 1, a method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy is characterized in that: In S1, for each tugboat interference path, the interference azimuth θ of the current tugboat interference path is combined p , the towing distance and depth of the towed array and the interference azimuth interval corresponding to the sea depth setting [θ p - Δθ,θ p +Δθ], Δθ is the interference deviation angle.

3. The method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 2 is characterized in that: In the different tugboat interference paths, the interference deviation angle of the tugboat interference direct wave path is greater than the interference deviation angle of the tugboat interference seabed reflection path and the seabed-sea surface reflection path.

4. The method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 1, characterized in that: In S1, for each tugboat interference path, the interference azimuth θ aligned with the current tugboat interference path is p After beam output, the corresponding tugboat interference frequency domain waveform is obtained, and then the tugboat interference frequency domain waveform is inverse Fourier transformed to obtain the tugboat interference reference waveform i''(t) corresponding to the current tugboat interference path.

5. The method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 1, characterized in that: The S2 is specifically: S2.1: When receiving the transmission signal, align the current towed array sonar receiving waveform with the current interference azimuth of each towing ship interference path as a beam output to obtain the waveform to be decomposed; then perform successive variational mode decomposition on the current waveform to be decomposed to obtain multiple eigenmodes; S2.2: Calculate the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current interference path, select the eigenmode according to the power spectrum cross entropy and reconstruct the tugboat interference time domain waveform; S2.3: After reconstructing the waveform of each array element of the reconstructed tugboat interference time domain waveform in the array element domain, a reconstructed tugboat interference waveform is obtained, and the current towed array sonar receiving waveform and the reconstructed tugboat interference waveform are offset in the array element domain to obtain an updated towed array sonar receiving waveform; S2.4: Obtain a new interference azimuth angle after searching through broadband beamforming within the interference azimuth interval of the current tugboat interference path, repeat S2.1-S2.3, perform array element domain cancellation on the towed array sonar receiving waveform of the current tugboat interference path, traverse and search for the azimuth angle within the interference azimuth interval of the current tugboat interference path and process it until no tugboat interference is detected within the interference azimuth interval of the current tugboat interference path, thereby achieving tugboat interference suppression.

6. A method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 5, characterized in that: In S2.2, the calculation formula of the power spectrum cross entropy between each eigenmode and the tugboat interference reference waveform of the current tugboat interference path is as follows: H=-Σ Nh n=Nl P u (f n )log(P i (f n )) Where H is the power spectrum cross entropy of each eigenmode, P u (f n ) is each eigenmode u(t) at frequency f n The normalized power spectrum of the corresponding frequency point, P i (f n ) is the tugboat interference reference waveform i''(t) at frequency f n Normalized power spectrum of the corresponding frequency point; Nl is the lower limit frequency f of the Fourier transform of the towed array sonar receiving waveform l The corresponding frequency index value, Nh is the upper limit frequency f after Fourier transform of the towed array sonar receiving waveform h The corresponding frequency index value, n is the frequency index value.

7. The method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 5, characterized in that: In 2.2, the eigenmode is selected according to the power spectrum cross entropy and the tugboat interference time domain waveform is reconstructed, specifically: The power spectrum cross entropy is less than or equal to the preset entropy value H T After adding the eigenmodes in the time domain, the reconstructed tugboat interference time domain waveform i is obtained. new (t), the formula is as follows: i new (t)=Σ K k =1 u k (t) Among them, K is less than or equal to the preset entropy value H T The number of eigenmodes, u k (t) is the eigenmode that meets the power spectrum cross entropy decision criterion.

8. The method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy according to claim 5, characterized in that: In 2.3, after the reconstructed tugboat interference time domain waveform is reconstructed on the array element domain, the reconstructed tugboat interference waveform x is obtained. tow (t), the reconstruction formula is as follows: x tow (t)=IFFT[i new (t)exp(-j2πf(m-1)d cosθ p / c)],m=1,2,…M Where IFFT[ ] represents inverse Fourier transform, i new (t) represents the reconstructed tugboat interference time domain waveform, f represents the frequency, m represents the array element number of the towed array, d represents the array element spacing, θ p represents the interference azimuth of the current towing ship interference path, c represents the speed of sound in water, and M represents the number of towline array elements.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, wherein: When the processor executes the computer program, the steps of a method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy as described in any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a method for suppressing tugboat multipath interference based on successive variational mode decomposition and cross entropy as described in any one of claims 1 to 8 are implemented.

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