Indirect-coherent measurement method for forward sound scattering target intensity of underwater object

Abstract

The invention belongs to the technical field of underwater acoustic measurement, and relates to an indirect-coherent measurement method for the forward acoustic scattering target intensity of an underwater object. The method comprises the following steps: respectively carrying out background field measurement when an underwater object does not exist and target field measurement when the underwater object exists, and storing and recording receiving signals of an observation channel and a reference channel; based on the measurement signals of the background field and the target field, through time delay estimation and signal coherence subtraction processing, forward sound scattering signals of the underwater object are extracted; and calculating the forward sound scattering target intensity of the underwater object by using the extracted forward sound scattering signal based on the sound propagation loss estimation and the signal power. According to the method, after the forward sound scattering wave signal of the object is extracted, the definition formula of the target intensity in the sonar equation is directly used for measuring and calculating the forward sound scattering target intensity, the number of calculation links is small, and the calculation efficiency is high.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of underwater acoustic measurement, and relates to an indirect-coherent measurement method for forward acoustic scattering target strength of an underwater object. BACKGROUND

[0002] Forward acoustic scattering has been considered as one of the four basic detection modes of sonar, and mainly utilizes the forward scattering wave (also known as diffraction wave) formed by the shielding of an underwater object to an incident sound wave to detect and identify the underwater object invading the bistatic receiving-transmitting line. Although theoretical analysis and numerical calculation results show that the forward scattering target strength of the object is greater than the backscattering and other lateral scattering target strengths, and there are preliminary laboratory measurement results, in actual application, the forward acoustic scattering wave will be disturbed by the direct penetrating wave from the sound source. In the forward acoustic scattering detection mode, due to the fact that the forward acoustic scattering wave and the direct penetrating wave arrive at the receiving end at nearly the same time, combined with the multipath effect of the ocean channel, it is almost impossible to separate the two kinds of sound waves by directly using the arrival time delay. Furthermore, since the strength of the forward acoustic scattering wave is far less than that of the direct penetrating wave, after the two kinds of waves are superimposed at the receiving end, the forward acoustic scattering wave is nearly completely hidden by the direct penetrating wave. Accurately separating the forward acoustic scattering wave from the strong interference background of the direct penetrating wave, or effectively suppressing the strong interference of the direct penetrating wave, is the basis for measuring the forward scattering target strength, and has important academic significance and practical value for further proving from the experimental measurement angle that the forward scattering target strength is greater than the backscattering and other lateral scattering target strengths.

[0003] The disclosed reference and technical materials show that there are two different methods for measuring the forward scattering target strength of an underwater object in the laboratory, the first one can be called a "direct-coherent" method, and the other one can be called a "direct-non-coherent" method. Both of the two methods directly process and analyze the signals of the forward scattering receiving channel (or called observation channel) in the presence and absence of the scattering body, and obtain the forward acoustic scattering signal of the object, only the signal processing ideas are different.

[0004] The key of the "direct-coherent" method is to realize the clock synchronization between the transmitting end and the receiving end by hardware triggering, that is, to accurately obtain the time of the sound wave transmitted from the transmitting end to the receiving end when the signal is collected and recorded, which is equivalent to measuring the absolute time delay of the receiving end relative to the transmitting end. The outstanding advantage of the "direct-coherent" method is that it can accurately measure the absolute transmission time delay of the sound signal, and the scattered signal of the target can be obtained by directly subtracting the signals recorded in the presence and absence of the target. However, the method has the following disadvantages: it has high requirements for the transmitting and collecting hardware system, and it is not intuitive to measure the target strength by using the scattering far-field pattern function, which may introduce additional calculation errors. When the hardware conditions of the measurement experiment cannot guarantee the clock synchronization between the transmitting and receiving ends, an approximate processing method, the "direct-incoherent" method, can be used. Similar to the "direct-coherent" method, the "direct-incoherent" method also measures the observation channel signal when the underwater object exists and the observation channel signal when the underwater object does not exist . Since the clock synchronization between the transmitting and receiving ends cannot be guaranteed, the forward scattering wave of the object cannot be directly obtained by subtracting the two signals. The alternative measure is to calculate the cross-correlation function of and and extract the time delay difference (or relative time delay) of the arrival of the two sound signals at the receiving end according to the position of the maximum value of the cross-correlation function. According to the relative time delay, the two signals are "aligned" in time and then subtracted, and the difference signal Figure 1 is considered as the forward acoustic scattering signal of the target (see ). The corresponding formula is . The subsequent steps are similar to the "direct-coherent" method, and the scattering far-field pattern function of the target is calculated, and the forward acoustic scattering target strength of the object is calculated by substituting the relationship between the target strength and the scattering far-field pattern function.

[0005] When the amplitude of the forward scattering wave is much smaller than the amplitude of the straight-through wave, the "direct-incoherent" method can achieve good approximation effect; when the amplitude of the forward scattering wave increases (for example, in the typical normal incidence condition), the approximation error of the method also increases, and the approximation effect becomes worse. SUMMARY

[0006] In view of the deficiencies of the forward acoustic scattering target intensity measurement method under current laboratory conditions, the application provides an indirect-coherent measurement method for forward acoustic scattering target intensity of underwater objects, which adds a reference receiving channel to provide time delay difference auxiliary measurement on the basis of the original measurement system configuration, so that the phase difference between the straight-through wave and the interference superimposed wave can be accurately obtained without the need for the transmission-collecting hardware system to guarantee the clock synchronization of the transmission and reception ends; on the basis of the obtained forward scattering wave of the target, the sound velocity and the propagation loss measurement results are combined, and the forward acoustic scattering target intensity of the underwater object is directly measured according to the standard definition formula.

[0007] The technical scheme provided by the application is as follows: an indirect-coherent measurement method for forward acoustic scattering target intensity of underwater objects, comprising: (S1) measurement and recording step: respectively performing background field measurement when there is no underwater object and target field measurement when there is an underwater object, and recording the received signals of the observation channel and the reference channel; (S2) forward acoustic scattering signal extraction step: based on the measurement signals of the background field and the target field, the forward acoustic scattering signal caused by the underwater object is extracted through time delay estimation and signal coherent subtraction processing; (S3) target intensity calculation step: based on the sound propagation loss estimation and the signal power, the forward acoustic scattering target intensity of the underwater object is calculated by using the extracted forward acoustic scattering signal.

[0008] Preferably, the step (S1) comprises: (1) under the condition that there is no underwater object, a predetermined signal is emitted by controlling the underwater sound source, and the observation channel signal and the reference channel signal are recorded synchronously; (2) under the condition that there is an underwater object, the positions of the sound source and the receiving channel remain unchanged, after the object to be measured is placed, the same signal is emitted by controlling the sound source, and the observation channel signal and the reference channel signal are recorded synchronously.

[0009] Preferably, the step (S2) comprises sound velocity and propagation loss estimation: (1) the time delay difference is calculated based on the cross-correlation function of the signals of any two channels in the background field measurement, the sound velocity is estimated in combination with the channel spacing , and the arithmetic mean of multiple measurement values is taken as the sound velocity measurement value ; (2) the sound propagation loss is estimated based on the sound pressure power of the signals of each channel in the background field measurement and the sound source level of the transmitting transducer, and the sound propagation expansion law coefficient is determined by performing least square fitting with a theoretical model . .

[0010] Preferably, the extraction of the forward acoustic scattering signal in step (S2) specifically includes: (1) Calculate the reference channel signal under the background field and the target field. and The cross-correlation function is used to determine the relative time delay difference. ; (2) Calculate the observation channel signal under the background field With reference channel signal The cross-correlation function is used to determine the relative time delay difference. ; (3) Refer to the aforementioned time delay difference and Signal in the target field observation channel and background field observation channel signal The signals of the same duration are extracted and denoted as follows: and ; (4) Subtract the two time window signals to obtain the forward acoustic scattering signal: .

[0011] Preferably, step (S3) includes: (1) Establish a coordinate system with the target location as the origin, and determine the position coordinate vectors of the sound source, observation channel and reference channel. , , ; (2) Based on the established laws of sound propagation, calculate the propagation loss from the sound source to the object, the propagation loss from the object to the observation channel, and the propagation loss from the sound source to the reference channel; (3) Calculate the forward acoustic scattering signal power level And calculate the reference channel time window signal under the background field. power level .

[0012] Preferably, in step (S3), the forward acoustic scattering target intensity Calculated using the following formula: ; in, To observe the sensitivity of the hydrophone in the channel, The hydrophone sensitivity is used as a reference channel; , , These are the propagation losses from the sound source to the object, from the object to the observation channel, and from the sound source to the reference channel, respectively.

[0013] The present application has the advantages over the "direct-coherent" method in that the operation steps are simple, the hardware requirements for the experimental equipment are not high, and only a reference channel is needed to indirectly realize the phase synchronization of the measurement signals in the two states of "no underwater object" and "underwater object", without the need for the hardware system to ensure the clock synchronization of transmission and collection and thus ensure the phase synchronization of the signals. The present application has the advantages over the "direct-incoherent" method in that the phase difference between the straight-through wave and the interference superposition wave can be more accurately estimated and thus the forward acoustic scattering signal of the object can be extracted, instead of the projection of the forward acoustic scattering signal extracted by the "direct-incoherent" method in the direction of the interference superposition wave. Furthermore, after the forward acoustic scattering signal of the object is obtained by the "direct-coherent" method and the "direct-incoherent" method, the target strength is estimated by means of the scattering far-field pattern function of the object. The method of the present application directly utilizes the definition formula of the target strength in the sonar equation to measure the forward acoustic scattering target strength after the forward acoustic scattering wave signal of the object is extracted, with less calculation links and high calculation efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 A schematic diagram of the extraction of the forward acoustic scattering wave of an underwater object by the "direct-incoherent" method in the prior art; Figure 2 A schematic diagram of the extraction of the forward acoustic scattering wave of an underwater object by the "indirect-coherent" method provided by the present application; Figure 3 A top view of the layout of the anechoic tank experiment for the target strength measurement of a rusted steel cylindrical shell; Figure 4 The measurement results of the sound speed in water during the experiment; Figure 5 The experimental measurement results of the sound propagation spreading loss and the fitting curve thereof; Figure 6 An example of the signal phase alignment results of the reference channel (No. 6 channel); wherein (a) the signals and ; (b) the residual signal after the alignment of the two signals; Figure 7 An example of the signal phase alignment results of the observation channel (No. 2 channel); wherein (a) the signals and ; (b) the extracted forward acoustic scattering wave signal ; Figure 8 The measurement results of the forward acoustic scattering target strength of the No. 2 channel. DETAILED DESCRIPTION

[0015] With reference to the accompanying drawings, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of the present application.

[0016] In the examples of the present application, subscript "O" represents "observation channel", and subscripts "A" and "P" represent "no underwater object" and "underwater object" respectively; the reference receiving channel is marked with subscript "R".

[0017] Embodiment 1, the present application provides an indirect-coherent measurement method of forward acoustic scattering target strength of underwater object, which is suitable for measuring the forward acoustic scattering target strength of underwater object under laboratory (such as anechoic tank) conditions. After the whole measurement system is built, the technical solution can be divided into three implementation steps: measurement recording and labeling, forward acoustic scattering signal extraction and target strength calculation. The forward acoustic scattering signal extraction of underwater object is the core of the technical solution, and the principle is as shown in Figure 2 The complete implementation steps and operation process are as follows: 1. Measurement recording and labeling (1) Measurement recording and labeling when "no underwater object" (background field): the underwater sound source emits a set signal, and the observation channel and the reference channel synchronously receive and record signal data, wherein the signal of the observation channel is recorded as , and the signal of the reference channel is recorded as .

[0018] (2) Measurement recording and labeling when "underwater object" (target field): the underwater sound source and the positions of the receiving channels remain unchanged, and the object to be measured is placed at a predetermined position underwater; the sound source emits the same signal as when "no underwater object" is measured, and the observation channel and the reference channel synchronously receive and record signal data, wherein the signal of the observation channel is recorded as , and the signal of the reference channel is recorded as .

[0019] 2. Forward acoustic scattering signal extraction (3) Under the condition of "no underwater object", two receiving channels (channels i and j ) are arbitrarily selected, the time delay difference of the signals of the two channels is calculated by the cross-correlation function, and the distance between the two channels is divided by the time delay difference to obtain the speed estimation value . The arithmetic mean of the speed estimation values obtained by multiple measurements of different channel combinations is taken as the measured value of the speed under the experimental conditions .

[0020] (4) Under the condition of "no underwater object", calculate the electrical power of the measurement signal of each channel, and then calculate its sound pressure power in combination with the calibration value of the sensitivity level of the corresponding hydrophone. Then, based on the sound source level of the transmitting transducer at the signal frequency, estimate the sound propagation loss in the experiment, and compare it with the actual sound pressure level of the hydrophone. ( r To determine the propagation spread law of sound (i.e., to determine the propagation spread law coefficients), a least-squares fit is performed on the distance. (value).

[0021] (5) Reference channel received signal when calculating "no underwater object". Reference channel received signal when "underwater object is present" The cross-correlation function between the two signals is used to determine the relative time delay (or time delay difference) between them by identifying the location of the maximum cross-correlation value. .

[0022] (6) Calculate the reference channel received signal under the condition of "no underwater object". Signals from the observation channel The cross-correlation function between the two variables is used to determine the relative time delay (or time delay difference) between them based on the location of the maximum cross-correlation value. .

[0023] Reference delay difference and The relative time delay difference between them is used to extract the observation channel signal under the condition of "the presence of an underwater object" using time windows of the same length. and the observation channel signal when "no underwater object exists" ,get and The difference between the two signals is the forward acoustic scattering signal of the object. .

[0024] 3. Target Intensity Measurement (7) Establish a three-dimensional Cartesian coordinate system with the target location as the origin, and convert the measured relative distance information of the sound source, reference channel, and observation channel into position coordinates (the coordinates of the sound source, reference channel, and observation channel are successively converted into vectors). , , (Represented). Based on the sound wave propagation law calculated in step (4), calculate the sound propagation loss value from the sound source to the underwater object, the sound propagation loss value from the underwater object to the observation channel, and the sound propagation loss value between the sound source and the reference channel.

[0025] (8) Further calculate the result obtained in step (6) signal power level and used with Equal-length time windows are used to capture the reference channel signal. get Calculate the power level of the signal. .

[0026] (9) Substitute the propagation loss value calculated in step (7), the signal power level calculated in step (8), and the hydrophone sensitivity levels of the reference channel and the observation channel into the target strength calculation formula to obtain the forward scattering target strength. : ; in, To observe the sensitivity of the hydrophone in the channel, The hydrophone sensitivity is used as a reference channel; , , These are the propagation losses from the sound source to the object, from the object to the observation channel, and from the sound source to the reference channel, respectively.

[0027] Example 2: This invention demonstrates a specific implementation method by combining a target strength measurement experiment of a stainless steel cylindrical shell completed in a silencing water tank. (See attached document.) Figure 3 The layout of the transmitter, cylindrical shell, and receiver during the experiment is presented, and the distance parameters between the transmitter and receiver, measured with the target location as a reference point, are labeled. During the experimental measurements, the underwater depth of the transmitter, cylindrical shell, and receiver was consistently 2.0 m, and their positions remained fixed. The target rotated half a revolution around its center in the horizontal plane, which is the target's attitude angle relative to the incident wave from the sound source. Ψ It is variable, and the range is... Hydrophones 1-5 measure the target intensity in the forward-scattered far field. Hydrophone 6 is the reference channel in this invention. Hydrophone 8 measures the target intensity in the forward-scattered near field. Hydrophone 7 measures the target intensity in the backscattered far field, which is unrelated to the content of this invention. The sensitivity levels of the hydrophones in all receiving channels are... Test and measurement data are available for all channels: Channels 1, 6, 7, and 8. Values ​​are -160 dB, -163 dB, -160 dB, -161 dB; channels 2-5 The values ​​were all around -190 dB. In the experiment, a spherical transducer was used as the transmitter, and the transmitted signal was a CW pulse signal with a center frequency of 30 kHz and a pulse width of 20 carrier cycles, with a repetition period of 1.0 s.

[0028] (1) When conducting the "no underwater object" measurement, the signals received and recorded by channels 1-5 are labeled as follows: , , , , , the signal received by the 6th channel is marked as , the signal received by the 8th channel is marked as .

[0029] (2) When measuring the "existence of underwater objects", the signals received by the 1st-5th channels are marked in turn as: , , , , , the signal received by the 6th channel is marked as .

[0030] (3) Using the measurement data when there is no underwater object, select any two receiving channels (for example, channels 1 and 6) from the 1st-5th, 6th and 8th channels, calculate the cross-correlation functions of the signals and and determine the time delay difference of the two channels through the position of the maximum cross-correlation value , then the sound speed estimate is the ratio of the distance between the two channels and the time delay difference, that is . According to this, the sound speed measurement and estimation under other channel combinations are completed, and the arithmetic mean of the sound speed values measured under all channel combinations is taken as the measured value of the sound speed under the experimental conditions , the results are shown in the attached Figure 4 . The measured result shows that the sound speed value in the anechoic tank is about 1486 m / s, close to the sound speed value of fresh water in summer, which conforms to the objective reality.

[0031] (4) Then according to the receiving-transmitting layout relationship shown in the attached Figure 3 , the distance from the 6th channel to the sound source is calculated directly , and the distance from the 8th channel to the sound source is calculated directly . The corresponding sound power values and are calculated from the signals received by the 6th and 8th channels respectively and , and combined with the receiving sensitivity values of the two channels, the sound pressure levels at the two distances can be obtained and . Since the lateral aperture (0.9 m) covered by the 1st-5th channels is much smaller than the horizontal distance (14.1 m) to the sound source, the arithmetic mean of the sound pressure levels of these five channels is taken as the sound pressure level at the observation distance of 14.1 m (the 3rd channel) . Thus the sound pressure levels at three horizontal distances of 4.43 m, 7.13 m and 14.10 m are obtained , and The sound source level of the transmitting transducer at 30 kHz was then determined, and the estimated sound propagation loss under the experimental conditions is shown in the attached figure. Figure 5 As shown. The measurement results show that the sound propagation loss during the experiment follows a spherical propagation law as distance increases, i.e. .

[0032] (5) Calculation and The cross-correlation function between the two signals is used to determine the relative time delay between them by identifying the location of the maximum cross-correlation value. Based on this relative time delay, the start times of the two signals in the time domain are "aligned," and the results are shown in the appendix. Figure 6 As shown in the figure, the blue curve represents the residual signal after the two signals are aligned, and its amplitude is much smaller than that of the residual signal. and The amplitude indicates that it was determined by calculating the cross-correlation function. and The relative time delay between them is guaranteed to have a certain degree of accuracy.

[0033] (6) If channel 2 is selected as the observation channel, then calculate... and The cross-correlation function between the two is used to determine the relative time delay between them based on the location of the maximum cross-correlation value. .in accordance with and The relative time delay difference between them is used to extract the observation signal when "underwater object exists" using time windows of the same length. Observation signals when "no underwater objects exist" ,get and Subtracting the two signals gives the forward acoustic scattering signal of the object. Appendix Figure 7 The processing results for this step are shown, where the black solid line and the red solid line represent... and The blue solid line represents the extracted... The signal is used for subsequent calculations of the electrical power level of the forward acoustic scattering signal. .

[0034] (7) Attachment Figure 3 The location of the target is set as the origin, and a three-dimensional Cartesian coordinate system is established. Based on the measured relative distance information, the position coordinates of the sound source, reference channel, and observation channel are obtained, as shown in Table 1. The propagation loss from the sound source to the target is calculated based on the sound propagation extension law obtained in step (4). The acoustic propagation loss from the target to the second observation channel is... ; and the sound propagation loss value between the sound source and the reference channel is .

[0035] Table 1. List of position coordinates of sound source and receivers .

[0036] (8) For all the target aspect angle values, calculate the signal electric power level of the signal obtained in step (6) (8) For all the target aspect angle values, calculate the signal electric power level of the signal obtained in step (6) (the value is different for different values of Ψ , for example, the result is 0.0016 dB when ); use the same time window as the time length of to intercept to obtain , and calculate the electric power level of the signal (the value is a fixed value).

[0037] (9) Substitute the propagation loss value TL S , TL O2 and TL RS , the signal electric power level and calculated in step (8), the hydrophone sensitivity level of channel No. 6 and the hydrophone sensitivity level of channel No. 2 into the target intensity calculation formula to obtain the estimated value of the forward scattering target intensity , and the results are shown in the attached Figure 8 , in which the red solid line marked is the measurement result of the "indirect-coherent" method, the blue solid line marked is the measurement result of the "indirect-incoherent" method, and the black dashed line is the numerical result of the forward acoustic scattering target intensity of the stainless steel cylindrical shell calculated by the Kirchhoff integral approximation method.

[0038] The results show that: (1) the forward scattering target intensity value of the "indirect-coherent" method is generally higher than the measurement result of the "direct-incoherent" method, which can confirm that the forward acoustic scattering signal extracted by the "direct-incoherent" method is the projection of the real forward acoustic scattering signal in the direction of interference superposition wave signal. (2) Within the aspect angle interval of , the matching degree of the forward acoustic scattering target intensity measurement result obtained by the "indirect-coherent" method to the typical numerical solution is obviously better than the measurement result of the "direct-incoherent" method. (3) Within the aspect angle interval of The deviation between the measurement results of the "indirect-coherent" method and the typical numerical results is higher than the deviation corresponding to the "direct-incoherent" method in the attitude angle interval. The reason for this phenomenon is that the hydrophone sensitivity level of the observation channel (channel No. 2) is about 27 dB lower than the sensitivity level of the reference channel (channel No. 6), and the measurement results at this time have not been accurate enough. If the hydrophone with the same or similar sensitivity level as the reference channel is also used in the observation channel, the measurement deviation in this attitude angle interval will certainly be further reduced as expected.

[0039] The embodiment shows that the "indirect-coherent" method proposed by the present application can effectively measure the forward acoustic scattering target strength of the underwater object, and the measurement results are overall better than the measurement results of the "direct-incoherent" method, especially in the interval of the incident attitude angle Although only the forward scattering target strength of the regular-shaped scattering body such as the finite-length stainless steel cylindrical shell is measured in the anechoic tank laboratory condition here, it can be inferred from the effectiveness of the measurement results that the "indirect-coherent" method is also applicable to the field test environment with stable or slowly-varying environment, and is also applicable to the scattering body with complex shape or internal structure.

Claims

1. An indirect-coherent method for measuring the intensity of forward acoustic scattering from an underwater object, characterized in that, include: (S1) Measurement and recording steps: Perform background field measurement when there are no underwater objects and target field measurement when there are underwater objects, and record the received signals of the observation channel and the reference channel. (S2) Forward acoustic scattering signal extraction step: Based on the measured signals of the background field and the target field, the forward acoustic scattering signal caused by the underwater object is extracted by time delay estimation and signal coherent subtraction. (S3) Target strength calculation steps: Based on the sound propagation loss estimation and signal power, the forward sound scattering target strength of the underwater object is calculated using the extracted forward sound scattering signal.

2. The method according to claim 1, characterized in that, The step (S1) includes: (1) Under the condition that there are no underwater objects, control the underwater sound source to emit a predetermined signal and simultaneously record the signal of the observation channel. and reference channel signal ; (2) In the presence of an underwater object, keep the positions of the sound source and the receiving channel unchanged. After placing the object to be measured, control the sound source to emit the same signal and synchronously record the signal of the observation channel. and reference channel signal .

3. The method according to claim 1 or 2, characterized in that, Step (S2) includes estimating the speed of sound and propagation loss: (1) Calculate the arrival time delay difference based on the cross-correlation function of any two channel signals in the background field measurement. Combined with channel spacing Estimating the speed of sound The arithmetic mean of multiple measurements was taken as the sound speed measurement value. ; (2) Based on the sound pressure power of each channel signal and the sound source level of the transmitting transducer in the background field measurement, the sound propagation loss is estimated and compared with the theoretical model. Perform least-squares fitting to determine the coefficients of sound propagation spread. .

4. The method according to claim 3, characterized in that, The extraction of the forward acoustic scattering signal in step (S2) specifically includes: (1) Calculate the reference channel signal under the background field and the target field. and The cross-correlation function is used to determine the relative time delay difference. ; (2) Calculate the observation channel signal under the background field With reference channel signal The cross-correlation function is used to determine the relative time delay difference. ; (3) Refer to the aforementioned time delay difference and Signal observed in the target field channel and background field observation channel signal The signals of the same duration are extracted and denoted as follows: and ; (4) Subtract the two time window signals to obtain the forward acoustic scattering signal: .

5. The method according to claim 4, characterized in that, The step (S3) includes: (1) Establish a coordinate system with the target location as the origin, and determine the position coordinate vectors of the sound source, observation channel and reference channel. , , ; (2) Based on the established laws of sound propagation, calculate the propagation loss from the sound source to the object, the propagation loss from the object to the observation channel, and the propagation loss from the sound source to the reference channel; (3) Calculate the forward acoustic scattering signal power level And calculate the reference channel time window signal under the background field. power level .

6. The method according to claim 5, characterized in that, In step (S3), the forward acoustic scattering target intensity Calculated using the following formula: ； in, To observe the sensitivity of the hydrophone in the channel, The hydrophone sensitivity is used as a reference channel; , , These are the propagation losses from the sound source to the object, from the object to the observation channel, and from the sound source to the reference channel, respectively.

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