Target depth division method based on direct wave arrival angle difference

Abstract

The invention relates to a target depth division method based on a direct wave arrival angle difference. A horizontal line array is arranged in a known sea area of a deep sea, and a motion sound source linearly moves to pass through the forward end fire direction of the horizontal line array. And comparing the minimum value of the time-varying curve of the arrival angle of the linear array direct wave with the angle demarcation value of the same motion track characteristic of the known sea area to obtain the depth information of the motion sound source, namely, the depth of the motion sound source is smaller than the depth demarcation value or greater than the depth demarcation value. The depth demarcation value and the angle demarcation value can be quickly calculated according to simulation, in addition, parameter information corresponding to different target movement tracks of a known sea area can be calculated in advance, target depth classification can be quickly carried out, the calculation efficiency is greatly improved, and engineering practice is easy.

Description

Technical Field

[0001] The present invention belongs to the field of underwater acoustic signal processing, and relates to a method for dividing the depth of a target based on the difference in arrival angles of direct waves. It is applicable to quickly distinguishing surface and underwater targets based on a horizontal line array, and belongs to the fields of ocean engineering, underwater acoustic engineering, array signal processing, sonar technology, etc. Background Art

[0002] With the rapid development of unmanned and information technologies, underwater detection based on unmanned underwater vehicles (UUVs) has become an important development trend. As a common target detection sonar, a horizontal line array sonar can be applied and promoted on various detection platforms. When used as an underwater target acoustic detection payload based on a UUV, common loading methods include a side array and a towed array. However, for a UUV platform with a small size, due to limited energy and space, the aperture of the horizontal line array is often restricted. For a small UUV, the reliable target detection range of its acoustic payload mainly focuses on the direct wave region at present.

[0003] Considering a UUV underwater cruise detection scenario, the UUV and the target often intersect, that is, the moving target appears directly in front of the UUV. At this time, due to the lack of directivity in the vertical dimension of a single horizontal line array, the incoming wave signals in the horizontal plane and the vertical plane cannot be distinguished, resulting in the signal arrival angle of the target appearing directly in front of the UUV not being 0 degrees, and this arrival angle is related to the depth. Therefore, the depth of the target can be distinguished by analyzing the angle change law before and after the intersection of the UUV and the target. Based on the above analysis, the present invention proposes a method for dividing the depth of a target based on the difference in arrival angles of direct waves. By analyzing the relationship between the direct wave arrival angle and the target depth and comparing it with the copy field data, the depth division of the moving target can be quickly realized. Summary of the Invention

[0004] Technical Problems to be Solved

[0005] In order to avoid the deficiencies of the prior art, the present invention proposes a method for dividing the depth of a target based on the difference in arrival angles of direct waves to distinguish targets at different depths;

[0006] The method of the present invention uses a horizontal line array to estimate the azimuth of the direct wave of a moving sound source passing through the end-fire direction of the line array, and divides the target depth by analyzing the change law of the direct wave arrival angle. This method has the characteristics of strong real-time performance and wide application range, can adapt to various environmental changes, and provides reliable technical support for fields such as ocean monitoring and underwater defense.

[0007] Technical Solution

[0008] A method for dividing the target depth based on the difference in arrival angles of direct waves, characterized by the following steps:

[0009] Step 1: Estimate the minimum value θ of the arrival angle of the direct wave using the spectral estimation method estimin ;

[0010] Step 2: Calculate the angle boundary value θ for target depth division using the acoustic field model crit , defined as the arrival angle θ of the direct wave corresponding to the target depth d = 0m crit = θ arr (d = 0m);

[0011] Step 3: Calculate the angle difference between the minimum value θ of the arrival angle of the direct wave estimin and the angle boundary value θ crit , and divide the target depth by the angle difference.

[0012] The division criterion for dividing the target depth by the angle difference is: Calculate Δθ = θ estimin - θ crit , when Δθ > 0°, it means the target depth is greater than the depth boundary value D crit ; when Δθ < 0°, it means the target depth is less than the depth boundary value D crit .

[0013] The depth boundary value D crit is defined as: as the target depth d increases, when the arrival angle of the direct wave is equal to the arrival angle of the direct wave corresponding to the target depth d = 0m, the depth at this time is defined as the depth boundary value D crit , satisfying θ arr (D crit ) = θ crit .

[0014] The calculation of the minimum value θ of the arrival angle of the direct wave estimin is: First, use the conventional beamforming method to estimate the arrival angle of the direct wave at a certain moment, that is, the target azimuth estimation value θ esti , and the target azimuth estimation values at different moments form a function of time, denoted as θ esti (t), and when the target intersects with the UUV, there is a minimum value of θ estimin .

[0015] The conventional beamforming method for estimating the arrival angle of the direct wave, that is, the target azimuth estimation value θ esti is: The azimuth corresponding to the maximum value of the beam output power is the azimuth estimation value: θ esti = argmax(P dB (θ)); where: P dB (θ) is the normalized decibel value of the output power of the conventional beamformer, that is: P dB($\theta$) = 20lg(P($\theta$) / max(P($\theta$))), where P($\theta$) is the output power of the beamformer.

[0016] The calculation of the output power of the beamformer: P($\theta$) = w($\theta$) H R x w($\theta$); where: R x represents the covariance matrix of the array received signals, w($\theta$) represents the beam weighting vector, and H represents the transpose symbol.

[0017] The arrival angle $\theta$ of the direct wave arr is calculated by using the Bellhop toolbox to calculate the arrival angle $\theta$ arr (d) corresponding to different target depths d. When calculating, the horizontal distance between the moving target and the UUV during intersection is known as R, and the receiving depth of the horizontal array is D rec , and the local hydrographic environment information of the UUV needs to be combined.

[0018] Step 1 and Step 2 are completed synchronously or Step 2 is carried out first, and then Step 1 is implemented.

[0019] An electronic device, characterized in that it includes a processor and a memory. When the processor executes the computer program stored in the memory, it realizes the data migration steps of the target depth division method based on the direct wave arrival angle difference as described.

[0020] A computer program product, characterized in that it includes computer executable instructions, and the instructions are used to realize the target depth division method based on the direct wave arrival angle difference when executed.

[0021] Beneficial effects

[0022] A target depth division method based on the direct wave arrival angle difference proposed by the present invention. In a deep - sea known sea area, there is a horizontal line array, and a moving sound source moves linearly through the forward end - fire direction of the horizontal line array. By comparing the minimum value of the direct wave arrival angle curve of the line array with time with the angle boundary value of the same moving trajectory characteristic in the known sea area, the depth information of the moving sound source can be obtained, that is, the depth of the moving sound source is less than the depth boundary value or the depth of the moving sound source is greater than the depth boundary value. The present invention can quickly calculate the depth boundary value and the angle boundary value according to the simulation. In addition, the parameter information corresponding to different target movement trajectories in the known sea area can be calculated in advance, which is convenient for quickly classifying the target depth, greatly improving the calculation efficiency and being easy for engineering practice. Description of the drawings

[0023] Figure 1 : Sound speed profile used in the simulation - Munk sound speed profile

[0024] Figure 2: Top view of the scenario

[0025] Figure 3 : Method flow chart

[0026] Figure 4 : Conventional beamforming output of the horizontal line array at time t1

[0027] Figure 5 : Curve of the estimated target azimuth changing with time

[0028] Figure 6 : Curve of the minimum arrival angle of the direct wave of the line array changing with the depth of the sound source Specific implementation manner

[0029] The present invention will be further described in combination with embodiments and drawings:

[0030] Deep - sea environment configuration and array signal simulation:

[0031] To verify the effectiveness of the method of the present invention, a computer simulation experiment is carried out. In this embodiment, a typical deep - sea environment is considered, with a sea depth of 5000 m, and the Munk sound - speed profile is as shown in the appendix Figure 1 The sound speed at the sea surface is 1550 m / s, the depth of the sound - channel axis is 1100 m, the sound speed at the sound - channel axis is 1500 m / s, the critical depth is 4430 m, and the sound speed at the seabed is 1552 m / s. The area above the sea surface is modeled as a vacuum environment, and the seabed is modeled as an acoustic half - space. The specific parameters related to the seabed sediment are as follows: the sediment sound speed is 1600 m / s, the sediment density is 1.8 g / cm 3 , and the sediment attenuation coefficient is 0.8 dB / λ.

[0032] The top view of the relative position of the regularly moving sound source and the M = 20 - element line array is as shown in the appendix Figure 2 The moving sound source moves in a straight line through the forward end - fire direction of the line array and continuously radiates a single - frequency regular sound signal with a frequency f = 750 Hz to the horizontal line array. At time t1, the moving sound source is located on the port side of the horizontal array, with a distance r1 = 1500 m and an azimuth θ1 = 45°. At time t2, the moving sound source is located on the starboard side of the horizontal array, with a distance r2 = 2000 m and an azimuth θ2 = 45°. The speed of the moving sound source is 3 m / s. The depth D of the moving sound source soc = 300 m, and the depth D of the receiving array rec = 50 m.

[0033] Combining the environmental and scenario information, under the assumption of a far - field plane wave, the Bellhop toolbox is used to simulate the signals x(t) received by the horizontal line array at different times within the time range of t1 - t2, that is, the target movement time.

[0034] According to the design scheme provided by the present invention, a method flow chart for target depth division based on the difference in arrival angles of direct waves is as shown in the appendixFigure 3 As shown in the figure, the steps are as follows:

[0035] Step 1: Estimate the minimum value θ of the arrival angle of the direct wave using the spectral estimation method estimin .

[0036] Azimuth estimation value θ esti

[0037] Sub-step 1: Estimate the arrival angle of the direct wave using the conventional beamforming method.

[0038] Assume that the number of horizontal array elements is M and the element spacing is d. Perform conventional beamforming on the array received signal to calculate the target azimuth estimation value θ esti . The specific process is as follows:

[0039] The conventional beamforming method is calculated by the following formula,

[0040] P(θ) = w(θ) H R x w(θ), (1)

[0041] where P(θ) represents the output power of the beamformer, R x represents the covariance matrix of the array received signal, w(θ) represents the beam weighting vector, and H represents the transpose symbol.

[0042] In practical applications, the output power of the beamformer is often normalized to decibels, that is

[0043]

[0044] The azimuth corresponding to the maximum value of the beam output power is the azimuth estimation value θ esti , that is,

[0045] θ esti = argmax(P dB (θ)). (3)

[0046] In the formula 1

[0047] The R x is calculated by the following formula,

[0048] R x = E[x(t0)x(t0) H , (4)

[0049] where x(t0) is the acoustic signal received by the horizontal array at time t0, and E[.] represents taking the expectation.

[0050] The w(θ) is calculated by the following formula,

[0051]

[0052] Among them, c is the reference sound speed, defined as the sound speed value at the receiving depth of the horizontal array, d is the element spacing, M is the number of array elements, and f is the signal frequency.

[0053] In the embodiment:

[0054] Take the signal x(t1) received by the horizontal line array at time t1, and the process of estimating the arrival angle of the direct wave using the conventional beamforming method is as follows:

[0055] (1) Substitute the array received signal x(t1) into Equation (4) to calculate the covariance matrix R of the array received signal x ;

[0056] (2) Substitute the element spacing d = 2m, the number of array elements M = 20, the signal frequency f = 750 Hz, and the reference sound speed c = 1500 m / s into Equation (5) to calculate the beam weighting vector w(θ);

[0057] (3) Substitute the R x and w(θ) obtained from the above two steps into Equation (1) to calculate the output power P(θ) of the beamformer;

[0058] (4) Substitute the output power P(θ) of the beamformer into Equation (2) to calculate the result P dB (θ) after normalizing the output power of the beamformer and taking decibels;

[0059] (5) According to Equation (3), the azimuth corresponding to the maximum value of the beam output power is the azimuth estimation value θ esti .

[0060] The result after normalizing the output power of the conventional beamforming and taking decibels is as shown in the appendix Figure 4 , and the azimuth estimation value is 45.4° at this time.

[0061] Sub-step two: Calculate the minimum value θ of the target azimuth estimation value estimin .

[0062] The target azimuth estimation value θ esti is a function of time, denoted as θ esti (t), and it has a minimum value when the target intersects with the UUV, denoted as θ estimin , that is,

[0063] θ estimin = min(θ esti (t)). (6)

[0064] In the embodiment:

[0065] For the horizontal line array from t1 to t2, that is, within the target motion time range, the above five steps of Sub-step 1 are respectively executed on the signals received at different times, that is, the conventional beamforming method is used to estimate the arrival angle of the direct wave, and the target azimuth estimation value θ esti (t) is obtained.

[0066] Plot the curve of the target azimuth estimation value changing with time θ esti (t) as shown in the appendix Figure 5 . Substitute the target azimuth estimation value θ esti (t) into Equation (6) for calculation, and θ estimin = 9.4° can be obtained.

[0067] Step 2: Calculate the angle demarcation value θ crit between the water surface and the underwater target using the acoustic field model.

[0068] Sub-step 1: Simulate the arrival angle of the direct wave corresponding to targets at different depths.

[0069] Assume that the horizontal distance between the moving target and the UUV during the encounter is R, and the receiving depth of the horizontal array is D rec . Combining the local hydrographic environment information of the UUV, use the Bellhop toolbox to calculate the arrival angle of the direct wave θ arr (d) corresponding to targets at different depths.

[0070] In the embodiment:

[0071] It is known that the horizontal distance R = 1212 m between the moving target and the UUV during the encounter. Combining the local hydrographic environment information of the UUV, use the Bellhop toolbox to calculate the arrival angle of the direct wave θ arr (d) as shown in the appendix Figure 6 .

[0072] Sub-step 2: Calculate the angle demarcation value θ crit and the depth demarcation value D crit .

[0073] The angle demarcation value θ crit is defined as the arrival angle of the direct wave corresponding to the target depth d = 0 m, that is,

[0074] θ crit = θ arr (d = 0 m) (7)

[0075] As the target depth d increases, when the simulated arrival angle of the direct wave is equal to the arrival angle of the direct wave corresponding to the target depth d = 0 m, the depth where it is located is defined as the depth demarcation value D crit , that is, it satisfies

[0076] θ arr (Dcrit ) = θ crit (8)

[0077] In the embodiment:

[0078] Analysis appendix Figure 6 , combined with the angle demarcation value θ in formula (7) crit , take the arrival angle of the direct wave corresponding to the target depth d = 0m as the angle demarcation value θ crit , that is, θ crit = 4.9°, combined with the definition of the depth demarcation value D in formula (8) crit , calculate the depth at which the arrival angle of the direct wave is equal to the arrival angle of the direct wave corresponding to the target depth d = 0m, that is, D crit = 208m.

[0079] Step three: Calculate the angle difference to divide the target depth

[0080] Compare the minimum value θ of the target azimuth estimation value estimin with the angle demarcation value θ crit , calculate the angle difference

[0081] Δθ = θ estimin - θ crit (9)

[0082] When Δθ > 0°, it means that the target depth is greater than the depth demarcation value D crit ; when Δθ < 0°, it means that the target depth is less than the depth demarcation value D crit .

[0083] In the embodiment:

[0084] According to formula (9), calculate the angle difference Δθ = θ estimin - θ crit = 9.4° - 4.9° = 4.5°, since Δθ > 0°, it means that D soc > D crit , that is, the target depth is greater than the depth demarcation value.

[0085] The present invention is not only applicable to the side conformal array, but also applicable to other horizontal line arrays such as the towed line array.

[0086] The present invention is not only applicable to the conventional beamforming method, but also applicable to other methods that can be used for azimuth estimation.

[0087] The present invention is applicable to the sea area where there is a direct wave between the target and the receiving array.

Claims

1. A method for dividing the target depth based on the difference in arrival angles of direct waves, characterized in that The steps are as follows: Step 1: Estimate the minimum value θ of the arrival angle of the direct wave using the spectral estimation method estimin ; Step 2: Calculate the angular demarcation value θ for target depth division using the sound field model crit , defined as the arrival angle θ of the direct wave corresponding to the target depth d = 0m crit = θ arr (d = 0m); Step 3: Calculate the minimum value θ of the arrival angle of the direct wave estimin and the angular demarcation value θ crit to divide the target depth by the angular difference.

2. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 1, wherein: The division criterion for dividing the target depth by the angular difference is: calculate Δθ = θ estimin - θ crit , when Δθ > 0°, it means that the target depth is greater than the depth boundary value D crit ; when Δθ < 0°, it means that the target depth is less than the depth boundary value D crit .

3. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 2, characterized in that: The depth demarcation value D crit is defined as: as the target depth d increases, when the arrival angle of the direct wave is equal to the arrival angle of the direct wave corresponding to the target depth d = 0m, the depth at which it is located is defined as the depth demarcation value D crit , satisfying θ arr (D crit ) = θ crit .

4. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 1, wherein: The minimum value θ of the arrival angle of the direct wave estimin is calculated as follows: First, use the conventional beamforming method to estimate the arrival angle of the direct wave at a certain moment, that is, the target azimuth estimation value θ esti , and the target azimuth estimation values at different moments form a function of time, denoted as θ esti (t). When the target intersects with the UUV, the minimum value is θ estimin。 5. The target depth division method based on the difference in arrival angles of direct waves according to claim 4, characterized in that: The conventional beamforming method estimates the arrival angle of the direct wave, i.e., the target azimuth estimation value θ esti which is: the azimuth corresponding to the maximum value of the beam output power is the azimuth estimation value: θ esti = argmax(P dB (θ)); where: P dB (θ) is the decibel value obtained by normalizing the output power of the conventional beamformer, i.e.: P dB (θ) = 20lg(P(θ) / max(P(θ))), P(θ) is the output power of the beamformer.

6. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 5, wherein: Output power calculation of the beamformer: P(θ) = w(θ) H R x w(θ); where: R x represents the covariance matrix of the array received signals, w(θ) represents the beam weighting vector, and H represents the transpose symbol.

7. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 1, wherein: The arrival angle θ of the direct wave arr is calculated by using the Bellhop toolbox to calculate the arrival angle θ of the direct wave corresponding to different target depths d arr (d). When calculating, the horizontal distance at the intersection of the moving target and the UUV is known as R, and the receiving depth of the horizontal array is D rec , and it is necessary to combine the local hydrographic environment information of the UUV.

8. The method for dividing target depth based on the difference in arrival angles of direct waves according to claim 1, wherein: Step 1 and Step 2 are completed synchronously or Step 2 is performed first and then Step 1 is implemented.

9. An electronic device, characterized in that, It includes a processor and a memory. When the processor executes the computer program stored in the memory, it implements the data migration steps of the target depth division method based on the difference in arrival angles of direct waves as described in any one of claims 1 to 7.

10. A computer program product, characterized in that It includes computer-executable instructions that, when executed, are used to implement the target depth division method based on the difference in arrival angles of direct waves as described in any one of claims 1 to 7.

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