A method for suppressing direct wave signal of a continuous wave active sonar detection system

Abstract

The application belongs to the technical field of underwater acoustic signal processing, and provides a direct wave signal suppression method of a continuous wave active sonar detection system, comprising the following steps: obtaining a receiving signal of a hydrophone and calculating an original time-frequency spectrum of the sound intensity of the receiving signal; performing first filtering processing on the original time-frequency spectrum, wherein the first filtering processing is used for filtering a continuous direct wave main component term in the original time-frequency spectrum; performing second filtering processing on the result of the first filtering processing, wherein the second filtering processing is used for filtering a continuous direct wave-target echo interference term in the result of the first filtering processing, and wherein logarithmic transformation is performed on the result of the first filtering processing before the second filtering processing is performed. The method provided by the application can effectively suppress the high-intensity direct wave signal component contained in the original underwater acoustic signal received by a bistatic continuous wave active sonar system.

Description

Technical Field

[0001] This application belongs to the field of underwater acoustic signal processing technology, specifically, it provides a method for suppressing direct wave signals in a continuous wave active sonar detection system. Background Technology

[0002] Bistatic active sonar detection systems employ a separate transmit and receive mechanism, where the active sonar transmits underwater acoustic signals, and the hydrophone receives them. Traditional active sonars mostly transmit pulse signals. Due to the intervals between pulses, it is relatively easy to separate the direct wave signal from the echo signal in the time domain within the underwater acoustic signal received by the hydrophone. In recent years, continuous wave active sonar detection systems have become increasingly widely used in underwater detection due to their higher time gain and larger detection range. Currently, continuous wave active sonars can transmit various forms of long-pulse continuous wave signals, such as linear frequency modulation (LFM) and hyperbolic frequency modulation (HFM). Because of these long pulse widths, the intensity of the direct wave signal (the signal that propagates directly from the active sonar to the hydrophone) is much higher than the target echo signal, thus masking weak echoes and creating a large detection blind zone.

[0003] Several schemes have been proposed to suppress the direct wave component in the received signal of a continuous wave active sonar detection system. However, these schemes have significant limitations: First, matched filter sidelobe suppression technology reduces matched filter sidelobes through window function methods or signal design (such as nonlinear frequency modulation), but its performance degrades or even fails when the signal is distorted or Doppler shifted in shallow sea dispersion channel environments. Second, spatial filtering methods create nulls in the direct wave azimuth based on beamforming techniques (such as blocking matrices and null constraints) to suppress interference, but this also suppresses the echo signal in that azimuth, creating a azimuth blind zone. Third, adaptive interference cancellation technology requires a clean direct wave reference signal, but in real-world environments, the reference signal is easily mixed with echoes or other interference, leading to performance degradation. It also has high computational complexity and is sensitive to channel time-varying characteristics. Finally, acoustic shielding technology cancels the direct wave by adjusting the transmitted signal, but this requires precise knowledge of the channel information, which is difficult to implement in real-world marine environments.

[0004] It is evident that for signal and information processing of bistatic continuous wave active sonar detection systems, there is an urgent need for a method that is simple in structure, low in computational complexity, robust to shallow sea dispersion channels, and applicable to various frequency modulation signal forms. This method should be able to efficiently suppress direct waves while completely preserving echo signals, thereby improving the discernibility of target echoes on time-frequency structure diagrams in low signal-to-noise ratio environments. Summary of the Invention

[0005] The purpose of this application is to provide a method for suppressing direct wave signals in a continuous wave active sonar detection system, the method comprising the following steps:

[0006] The received signal from the hydrophone is acquired and its original time spectrum of sound intensity is calculated. The received signal includes the continuous direct wave signal from the active sonar and the target echo signal.

[0007] The original time spectrum is subjected to a first filtering process, which is used to filter out the continuous direct wave principal component terms in the original time spectrum.

[0008] The result of the first filtering process is subjected to a second filtering process, which is used to filter out the continuous direct wave-target echo interference term in the result of the first filtering process. Before performing the second filtering process, the result of the first filtering process is subjected to a logarithmic transformation.

[0009] Furthermore, the target echo signal is the signal received by the hydrophone after the continuous signal emitted by the active sonar is reflected and scattered by the moving target; the number of the active sonar and the hydrophone is 1, and the positions of the active sonar and the hydrophone remain unchanged during the detection process.

[0010] Furthermore, both filtering processes include a two-dimensional Fourier transform operation, a binary mask operation, and a two-dimensional inverse Fourier transform operation.

[0011] Furthermore, the two-dimensional Fourier transform operation and the two-dimensional inverse Fourier transform operation are performed by equations (1) and (2), respectively:

[0012] (1),

[0013] (2),

[0014] in, , These are time variables and frequency variables, respectively. Two-dimensional spectrum in - Expressions of the domain , These are the independent variables of the two-dimensional Fourier transform. The imaginary unit, for Transform to - Expressions for the domain;

[0015] Furthermore, the binary masking operation is performed based on equation (3):

[0016] (3),

[0017] in, It is a binary mask matrix. Multiply the matrix elements one by one. To The result of performing a binary masking operation. and The dimensions are all with Maintain consistency.

[0018] Furthermore, the binary mask matrix As shown in equation (4):

[0019] (4).

[0020] Furthermore, and All are two-dimensional matrices, where, and The dimensions remain consistent, and middle Dimensions and middle The dimensions are all odd numbers.

[0021] Preferably, the energy of the principal component terms of the target echo signal is in - The distribution of the domain satisfies the energy dispersion condition shown in the following equation:

[0022] ,

[0023] in, The sound intensity time-frequency transformation of the principal components of the target echo signal to... - Expressions of the domain For the summation function, This is the preset dispersion threshold.

[0024] Furthermore, in the original time spectrum, the total energy of the continuous direct wave principal component term is much greater than the total energy of the continuous direct wave-target echo interferometry term, and the total energy of the continuous direct wave-target echo interferometry term is much greater than the total energy of the principal component term of the target echo signal.

[0025] This application provides a direct wave signal suppression method for a continuous wave active sonar detection system. It fully utilizes the different distribution characteristics of the target echo signal from a moving target and the direct wave signal from a stationary active sonar in the two-dimensional Fourier transform domain. By employing two filtering processes, it sequentially removes the principal component of the continuous direct wave and the interference term between the continuous direct wave and the target echo. This results in the interference structure characteristics reflected in the processed sound intensity time spectrum being dominated by the principal component of the target echo signal, with the intensity distributed within a reasonable upper and lower limit. The method employed in this application, from the perspective of sound field interference, utilizes the characteristic differences in interference fringes of different signals, exhibiting strong anti-interference capability in shallow sea dispersion channels and is not limited by the direction of arrival of the target echo and the direct wave. Attached Figure Description

[0026] Figure 1 A schematic diagram of the principle of a continuous wave active sonar detection system;

[0027] Figure 2 The acoustic intensity time spectrum of the target echo signal under ideal conditions;

[0028] Figure 3 The sound intensity time spectrum of the direct wave signal;

[0029] Figure 4 The frequency spectrum of the original received signal from the hydrophone;

[0030] Figure 5 The result is a two-dimensional Fourier transform of the acoustic intensity time spectrum of the target echo signal under ideal conditions.

[0031] Figure 6 The result is a two-dimensional Fourier transform of the sound intensity time spectrum of the direct wave signal;

[0032] Figure 7 This is a flowchart of a direct wave signal suppression method for a continuous wave active sonar detection system according to an embodiment of this application;

[0033] Figure 8 The result is a two-dimensional Fourier transform of the sound intensity time spectrum of the original received signal;

[0034] Figure 9 This is a schematic diagram of the result after the first filtering of the original time spectrum according to the embodiments of this application;

[0035] Figure 10 This is a schematic diagram of the result after the original time spectrum has undergone two filtering processes according to the embodiments of this application. Detailed Implementation

[0036] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0037] In the description of the embodiments of this application, it should be noted that if terms such as "upper," "lower," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use, they are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, in the description of this application, in order to distinguish different units, the terms "first," "second," etc. are used in this specification, but these are not limited by the manufacturing order, nor should they be construed as indicating or implying relative importance. Their names may differ in the detailed description and claims of this application.

[0038] The vocabulary used in this specification is for illustrative purposes and is not intended to limit the scope of this application. It should also be noted that, unless otherwise expressly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection via an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of these terms in this application.

[0039] In order to clearly explain the technical solution of this application, the working principle of the continuous wave active sonar detection system and the implementation mechanism of the technical solution adopted in this application will be explained first.

[0040] Figure 1 This is a schematic diagram of a continuous wave active sonar detection system. The X and Y directions in the diagram represent two orthogonal directions on the sea level, as shown below. Figure 1 As shown, in this detection system, the sound source is an active sonar capable of continuously emitting underwater acoustic signals in the 300-500Hz frequency band. This active sonar is located at a horizontal plane (0km, 5km), and the hydrophone is located at a horizontal plane (0km, 0km). Simultaneously, there is a moving target in the sea area where the detection system is located, and its position and direction of movement are... Figure 1 The middle section is indicated by a red line.

[0041] like Figure 1 As shown, the underwater acoustic signal emitted by the active sonar first undergoes a one-way sound propagation to reach the target's real-time location, then is scattered by the target. The scattered sound wave then undergoes another one-way sound propagation from the target to the hydrophone, forming the target echo signal. In addition, the acoustic signal emitted by the sound source can directly reach the hydrophone, forming a direct wave signal. The direct wave signal and the target echo signal together constitute the raw underwater acoustic signal received by this bistatic continuous wave sonar detection system.

[0042] When a target moves relative to an active sonar and hydrophone in the XOY plane, the target echo signal will exhibit obvious time-frequency interference characteristics. Figure 1 Taking the illustrated embodiment as an example, with the target's initial position at a horizontal plane (2km, -8km) and its final position at a horizontal plane (20km, 10km), moving at a constant speed (5m / s, 5m / s) along the red line direction, a short-time Fourier transform of the target echo signal can yield the following result: Figure 2 The time spectrum of the acoustic intensity of the target echo signal shown ,in , These are time and frequency variables, respectively.

[0043] from Figure 2 Two sets of interference fringes with different degrees of curvature can be observed. These two sets of fringes are caused by the motion of the target relative to the sound source and the target relative to the hydrophone, respectively. It should be noted that... Figure 2 The acoustic intensity time spectrum of the target echo signal shown This is the processing result under ideal conditions without direct wave interference. However, when a continuous wave active sonar continuously emits underwater acoustic signals, the raw underwater acoustic signal received by the hydrophone also includes the direct wave signal from the sound source to the hydrophone. Since there is no relative motion between the sound source and the hydrophone, the sound intensity time spectrum obtained by performing a short-time Fourier transform on the direct wave signal... like Figure 3 As shown, it has only one type of interference fringe without bending.

[0044] Furthermore, since the target echo signal is an underwater acoustic signal emitted by the active sonar, reflected by the moving target, and then received by the hydrophone, the intensity of the direct wave is much higher than the intensity of the target echo, such as... Figure 4 As shown, the original time spectrum of the sound intensity is obtained by performing a short-time Fourier transform on the raw underwater acoustic signal received by the hydrophone. The signal is almost entirely dominated by the direct wave signal. Obviously, if the direct wave signal cannot be effectively suppressed, it is impossible to extract effective information about the target from the received signal.

[0045] However, as analyzed in the background section, current direct wave signal component suppression schemes for continuous wave active sonar are either sensitive to the environment, have azimuth blind spots, or are computationally complex and difficult to adapt to actual marine environments.

[0046] To achieve simple, efficient, and universal suppression of direct wave signal components, the applicant first analyzed the characteristic distribution of the echo signal and the direct wave signal of the moving target in the time-frequency space to obtain the characteristic differences and separation difficulty of the two in different computational domains, and then determined the optimal scheme for suppressing the direct wave component.

[0047] Specifically, Figure 5 To Figure 2 acoustic intensity time spectrum of the target echo signal The result of performing a two-dimensional Fourier transform (2D FFT). Figure 6 To Figure 3 The sound intensity time spectrum of the direct wave signal The result of performing a two-dimensional Fourier transform. (Through...) Figure 5 and Figure 6 As can be seen, a two-dimensional Fourier transform is performed on the sound intensity frequency spectrum, resulting in... Domain transformation to After the target moves relative to the sound source and the hydrophone, and the relative positions between the sound source and the hydrophone remain unchanged, the target echo and the direct wave are separated. The distribution characteristics show obvious differences within the domain, with the energy of the direct wave component varying in... Concentrated in space On the vertical axis; at the same time, since there is an order of magnitude difference in intensity between the two (in some specific embodiments, the intensity of the direct wave component is much greater than that of the target echo component, for example, the intensity of the two components differs by more than three orders of magnitude), and the image features of the direct wave component after two-dimensional Fourier transform are extremely simple, it can be easily filtered out using a simple and convenient masking operation.

[0048] Based on the above analysis, this application provides a direct wave signal suppression method for continuous wave active sonar detection systems that differs from existing direct wave suppression technologies. (Refer to...) Figure 7 The method includes the following steps:

[0049] Step S1: Obtain the received signal from the hydrophone and calculate the original time spectrum of its sound intensity.

[0050] Based on the analysis above, for Figure 1 The continuous wave active sonar detection system shown above uses a hydrophone to receive signals. Continuous direct wave signal containing active sonar and target echo signal In some specific embodiments, a short time window can be used to slide across the received signal of the hydrophone and perform a short-time Fourier transform to obtain the spectrum at each time window. Then, the square of the modulus is taken to obtain the original time spectrum of the received signal intensity. For example, in one specific embodiment, the received signal is used for processing. The duration should be no less than 3600 seconds, and a time window of 3.6 seconds can be used. The original time spectrum generated by performing a short-time Fourier transform. The dimension is That is, 201 frequency points and 1001 time points, with a lower frequency limit of 300Hz and an upper frequency limit of 500Hz. See the intensity map for details. Figure 4 .

[0051] Step S2, for the original time spectrum Perform the first filtration process.

[0052] In embodiments of this application, the first filtering process includes the following steps:

[0053] First of all, Perform a two-dimensional Fourier transform operation to obtain its... - Domain representation Then, for Perform a binary masking operation to obtain the masked result. Finally, a two-dimensional inverse Fourier transform is performed to obtain the result of the first filtering. .

[0054] Generally, for any one - Two-dimensional spectrum of the domain Its two-dimensional Fourier transform is shown in equation (1):

[0055] (1),

[0056] in, , These are the independent variables of the two-dimensional Fourier transform. The imaginary unit, for Transform to - Expressions for the domain.

[0057] Accordingly, from - Domain transformation back - The two-dimensional inverse Fourier transform operation of the domain is shown in equation (2):

[0058] (2).

[0059] It should be understood that, in the field of signal processing technology, the above... , All are in the form of two-dimensional matrices.

[0060] Obviously, for the original time spectrum Substituting it into equation (1), we can obtain the result of the two-dimensional Fourier transform operation as shown in the following equation:

[0061] .

[0062] Figure 8 It shows the Figure 4 The original time spectrum shown The result of performing a two-dimensional Fourier transform ,pass Figure 8 It can be seen that, because the intensity of the continuous direct wave component is much greater than that of the target echo component in the original time spectrum, after the two-dimensional Fourier transform... exist The intensity of the bright line at this location is much higher than that at other locations, which causes the characteristics of the target echo signal to be compressed within the intensity range.

[0063] In this application - The filtering of continuous direct wave components in the domain is performed using a binary mask operation, the general form of which is shown in equation (3):

[0064] (3),

[0065] (3) In the formula It is a binary mask matrix. To be and The matrix elements are multiplied one-to-one. To The result of the binary masking operation, where, and The dimensions are all with Maintain consistency.

[0066] Accordingly, for Obtained through two-dimensional Fourier transform Substituting it into equation (3), we can achieve the binary masking operation shown in the following equation:

[0067] ,

[0068] To distinguish it from subsequent steps, the result of this binary masking operation is denoted as... .

[0069] The form determines in - The signal components filtered by the domain, due to the two-dimensional Fourier transform, Transform to - After the domain is defined, the distribution of continuous direct wave components becomes very easy to characterize. Therefore, the form of the binary mask matrix also becomes extremely simple. Preferably, It can be constructed using the form of equation (4):

[0070] (4),

[0071] That is, only need to Setting the matrix elements on the axis equal to 0 to zero, while keeping the values ​​at other positions unchanged, completes the process of... - The domain filters out continuous direct wave components.

[0072] Since binary masking is performed on... The matrix elements on the axis are set to zero. To facilitate this operation, in some preferred embodiments, the two two-dimensional spectra involved in equations (1) and (2) can be set to zero. and The dimensions remain consistent, and variable and Medium variables The dimensions are all odd numbers, for example, 1001 points each.

[0073] After completing the The binary mask operation is performed to obtain... Then, substituting it into equation (2), we can obtain the result of the first filtration process. Without loss of generality, the result of the first filtration process is denoted as... .

[0074] Figure 9 It shows the Figure 8 shown The result of the first filtration process As can be seen, the first binary masking operation enables... The continuous direct wave components that remain unchanged over time are filtered out, and the interference structure characteristics of the darker target echo signal are revealed.

[0075] However, Figure 9 The results cannot be used for target echo feature extraction based on signal strength because after the first binary masking operation, - There are still some brighter regions scattered throughout the domain, and the intensity of these regions is much higher than that of the interference structure of the target echo signal. This results in the intensity of the interference structure of the target echo signal being compressed to a low level. Furthermore, since the continuous direct wave components that remain unchanged over time are filtered out after the first binary masking operation, the intensity of the filtered regions also becomes extremely low. Therefore, it is impossible to distinguish between the two based on the difference in signal intensity.

[0076] The following analysis examines the generation mechanism of the brighter portion mentioned above. As discussed earlier, the signal received by the hydrophone... From continuous direct wave Composition and target echo composition Composition, that is The sound intensity of the received signal It can be expressed as equation (5):

[0077] (5),

[0078] Among them, superscript This indicates the conjugate transpose operation. This is an operation to extract the real part.

[0079] Observing equation (5), we can find that, It consists of three parts, among which, This represents the sound intensity when only a continuous direct wave exists in the received signal; in this application, this part is referred to as the continuous direct wave principal component term; similarly, This represents the sound intensity when only the target echo signal exists in the received signal. In this application, this part is referred to as the principal component of the target echo signal.

[0080] In addition to the principal component terms in the two ideal cases mentioned above, due to the interference between the continuous direct wave and the target echo, the result of the sound intensity calculation of the received signal also contains... This part is the result of the interference between the continuous direct wave and the target echo, which is referred to in this application as the continuous direct wave-target echo interference term.

[0081] During the initial filtering process, a two-dimensional Fourier transform is used to separate the principal components of the continuous direct wave. All concentrated in - domain On the axis, therefore the first binary masking operation can be performed from Eliminating direct wave principal component terms .

[0082] However, the first filtration process cannot remove... The reason for filtering this part is that it is the result of interference between a continuous direct wave with invariant time-frequency characteristics and a target echo with time-varying time-frequency characteristics. Therefore, directly performing a two-dimensional Fourier transform cannot eliminate this part. - The domain is concentrated in The shaft has simple structural features, therefore, this part cannot be filtered out by the first filtering process.

[0083] At the same time, considering For example, in some specific embodiments, Exceed Three orders of magnitude, therefore, in Much higher At the same time, It is also much higher than .

[0084] The above analysis leads to the conclusion that: after the first filtering process, the continuous direct wave principal component terms will be... After filtration, The bright spots present in the image are due to the continuous direct wave-target echo interferometry term, i.e. This is the cause.

[0085] In this application, this portion is much larger than the principal component of the target echo signal. The component removal is carried out in step S3, specifically, because That is, the sound intensity time spectrum at this time is the inner product of the continuous direct wave sound pressure and the target echo sound pressure. Therefore, it is necessary to first... Perform a logarithmic transformation, that is... Logarithmic operations are performed on each element in the equation. After the logarithmic operation, as shown in equation (6), the following can be obtained: The interference term becomes the summation term:

[0086] (6),

[0087] In formula (6), The cosine of the phase angle between the continuous direct wave signal and the target echo signal. It is a constant.

[0088] As can be seen from equation (6), after logarithmic operation, the continuous direct wave component that was originally coupled together in the time spectrum of sound intensity is separated from the target echo component. Simultaneously, considering the... Performing logarithmic operations does not affect its characteristics. - The form in the domain, therefore, after logarithmic processing, in step S3, the same steps as the first filtering process are used to perform a two-dimensional Fourier transform to... Transform to - The domain, and then the same equation (4) is used. A binary masking operation is performed to remove continuous direct wave components. Finally, a two-dimensional inverse Fourier transform is performed on the result after binary masking to obtain the result of the second filtering process. :

[0089] .

[0090] Figure 10 It shows the Figure 9 In The result after the second filtration process ,pass Figure 10 As can be seen, through two filtering processes, the continuous direct wave principal component and interference term contained in the sound intensity time spectrum of the hydrophone received signal can be filtered out in turn, so that the interference structure features reflected by the filtered time spectrum are dominated by the principal component of the target echo signal. Since the intensity of the interference structure of the target echo signal is higher than that of other locations at this time, intensity-based feature extraction can be easily performed on it.

[0091] Because the filtering operation based on binary masks used in this application directly converts the time spectrum into... - In the domain transformation result, some elements are set to zero. To avoid loss of effective information in the target echo signal, in some preferred embodiments, the characteristics of the moving target's echo signal can be further defined. Specifically, the energy of the principal component terms of the target echo signal is... - The distribution of the domain must satisfy the energy dispersion condition shown in equation (7):

[0092] (7),

[0093] in, The sound intensity time-frequency transformation of the principal components of the target echo signal to... - Expressions of the domain For the summation function, The preset dispersion threshold can be set, for example, to 0.1 or smaller. Equation (7) avoids the interference characteristics of the target echo signal from concentrating after transformation. The axis causes excessive target echo information to be filtered out as a continuous direct wave component during the binary masking process.

[0094] The specific embodiments of this application have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for suppressing direct wave signals in a continuous wave active sonar detection system, characterized in that, Includes the following steps: The received signal from the hydrophone is acquired and its original time spectrum of sound intensity is calculated. The received signal includes the continuous direct wave signal from the active sonar and the target echo signal. The original time spectrum is subjected to a first filtering process, which is used to filter out the continuous direct wave principal component terms in the original time spectrum. The result of the first filtering process is subjected to a second filtering process, which is used to filter out the continuous direct wave-target echo interference terms in the result of the first filtering process. Before performing the second filtering process, the result of the first filtering process is subjected to a logarithmic transformation. Both filtering processes include two-dimensional Fourier transform operations, binary masking operations, and two-dimensional inverse Fourier transform operations. The two-dimensional Fourier transform operation and the two-dimensional inverse Fourier transform operation are performed by equations (1) and (2), respectively: （1）， （2）， in, , These are time variables and frequency variables, respectively. Two-dimensional spectrum in - Expressions of the domain , These are the independent variables of the two-dimensional Fourier transform. The imaginary unit, for Transform to - Expressions for the domain; Furthermore, the binary masking operation is performed based on equation (3): （3）， in, It is a binary mask matrix. Multiply the matrix elements one by one. To The result of performing a binary masking operation. and The dimensions are all with Maintain consistency; The binary mask matrix As shown in equation (4): （4）。 2. The direct wave signal suppression method for a continuous wave active sonar detection system according to claim 1, characterized in that, The target echo signal is the signal received by the hydrophone after the continuous signal emitted by the active sonar is reflected and scattered by the moving target. The number of active sonar and hydrophone is 1, and the positions of active sonar and hydrophone remain unchanged during the detection process.

3. The direct wave signal suppression method for a continuous wave active sonar detection system according to claim 1, characterized in that, and All are two-dimensional matrices, where, and The dimensions remain consistent, and middle Dimensions and middle The dimensions are all odd numbers.

4. The direct wave signal suppression method for a continuous wave active sonar detection system according to claim 1, characterized in that, The energy of the principal component of the target echo signal is in - The distribution of the domain satisfies the energy dispersion condition shown in the following equation: ， in, The sound intensity time-frequency transformation of the principal components of the target echo signal to... - Expressions of the domain For the summation function, This is the preset dispersion threshold.

5. The direct wave signal suppression method for a continuous wave active sonar detection system according to claim 1, characterized in that, In the original time spectrum, the total energy of the continuous direct wave principal component term is much greater than the total energy of the continuous direct wave-target echo interferometry term, and the total energy of the continuous direct wave-target echo interferometry term is much greater than the total energy of the principal component term of the target echo signal.

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