A target depth segmentation method based on the angle of arrival difference of direct waves

Abstract

This invention relates to a target depth classification method based on the difference in arrival angle of direct waves. In a known deep-sea area, there is a horizontal linear array, and a moving sound source moves in a straight line through the array towards its forward trajectory. The minimum value of the curve showing the change in arrival angle of the direct waves over time is compared with the angle boundary value for the same motion trajectory characteristic in the known sea area to obtain the depth information of the moving sound source; that is, the depth of the moving sound source is either less than or greater than the depth boundary value. This invention can quickly calculate the depth boundary value and angle boundary value based on simulation. Furthermore, it can pre-calculate the parameter information corresponding to different target motion trajectories in the known sea area, facilitating rapid target depth classification, greatly improving computational efficiency, and is easy to implement in engineering practice.

Description

Technical Field

[0001] This invention belongs to the field of underwater acoustic signal processing and relates to a target depth segmentation method based on the angle of arrival difference of direct waves. It is applicable to the rapid differentiation of surface and underwater targets based on horizontal line arrays and belongs to the fields of marine engineering, underwater acoustic engineering, array signal processing, and sonar technology. Background Technology

[0002] With the rapid development of unmanned and information technologies, underwater detection based on Unmanned Underwater Vehicles (UUVs) has become an important development trend. Horizontal linear array sonar, as a common target detection sonar, can be widely applied on various detection platforms. When used as an acoustic detection payload for underwater targets on UUVs, common mounting methods include flank arrays and towed arrays. However, for smaller UUV platforms, due to limited energy and space, the aperture of the horizontal linear array is often restricted. For small UUVs, the reliable target detection range of their acoustic payloads is currently mainly concentrated in the direct wave region.

[0003] Consider a UUV underwater patrol and detection scenario where the UUV and target frequently intersect, meaning the moving target appears directly in front of the UUV. In this situation, because a single horizontal line array lacks vertical directional accuracy, it cannot distinguish between incoming wave signals in the horizontal and vertical planes. This results in the signal arrival angle of the target appearing directly in front of the UUV not being 0 degrees, and this arrival angle is depth-dependent. Therefore, the target depth can be distinguished by analyzing the angle change pattern before and after the UUV and target intersect. Based on the above analysis, this invention proposes a target depth classification method based on the direct wave arrival angle difference. By analyzing the relationship between the direct wave arrival angle and the target depth and comparing it with copied field data, the depth classification of moving targets can be quickly achieved. Summary of the Invention

[0004] Technical problems to be solved

[0005] To avoid the shortcomings of existing technologies, this invention proposes a target depth segmentation method based on the difference in the angle of arrival of direct waves, in order to distinguish targets at different depths;

[0006] This invention utilizes a horizontal linear array to estimate the direct wave azimuth of a moving sound source passing through the array's end-firing direction. The target depth is then defined by analyzing the variation in the direct wave arrival angle. This method is characterized by its strong real-time performance and wide applicability, adapting to various environmental changes and providing reliable technical support for fields such as marine monitoring and underwater defense.

[0007] Technical solution

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

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

[0010] Step 2: Calculate the angular boundary value θ used for target depth segmentation using the sound field model. crit θ is defined as the angle of arrival of the direct wave when the target depth d = 0 m. crit =θ arr (d=0m);

[0011] Step 3: Calculate the minimum value θ of the angle of arrival of the direct wave. estimin With the angular boundary value θ crit The angle difference is used to define the target depth.

[0012] The criterion for dividing target depth based on angle difference is as follows: calculate Δθ = θ estimin -θ crit When Δθ > 0°, it indicates that the target depth is greater than the depth boundary value D. crit When Δθ < 0°, it indicates that the target depth is less than the depth boundary value D. crit .

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

[0014] The minimum value of the angle of arrival θ of the direct wave estimin The calculation is as follows: First, the angle of arrival of the direct wave at a certain moment, i.e., the estimated target azimuth value θ, is estimated using conventional beamforming methods. esti The target azimuth estimates at different times constitute a function of time, denoted as θ. esti (t), which has a minimum value of θ when the target intersects with the UUV. estimin .

[0015] The conventional beamforming method estimates the angle of arrival of the direct wave, i.e., the target azimuth estimate θ. esti Yes: The azimuth estimate is the position corresponding to the point where the beam output power reaches its maximum value: θ esti =argmax(P dB (θ)); where: P dB (θ) is the normalized decibel value of the output power of a conventional beamformer, i.e.: P dB(θ)=20lg(P(θ) / max(P(θ))), where P(θ) is the output power of the beamformer.

[0016] The output power of the beamformer is calculated as follows: P(θ) = w(θ) H R x w(θ); where: R x Let w(θ) represent the covariance matrix of the array received signal, w(θ) represent the beam weighting vector, and H represent the transpose symbol.

[0017] The direct wave arrival angle θ arr The calculation involves using the Bellhop toolbox to calculate the direct wave arrival angle θ corresponding to different target depths d. arr (d) In the calculation, the horizontal distance between the moving target and the UUV at the intersection is known to be R, and the horizontal array receiving depth is D. rec Furthermore, it is necessary to combine local hydrological and environmental information of UUVs.

[0018] Step 1 and Step 2 can be completed simultaneously, or Step 2 can be performed first, followed by Step 1.

[0019] An electronic device is characterized by comprising a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement a data migration step as described in the target depth segmentation method based on the direct wave angle of arrival difference.

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

[0021] Beneficial effects

[0022] This invention proposes a target depth classification method based on the difference in arrival angle of direct waves. In a known deep-sea area, there is a horizontal linear array, and a moving sound source moves in a straight line through the array towards its forward trajectory. The minimum value of the curve showing the change in the arrival angle of the direct waves over time is compared with the angle boundary value for the same motion trajectory characteristic in the known sea area to obtain the depth information of the moving sound source; that is, the depth of the moving sound source is either less than or greater than the depth boundary value. This invention can quickly calculate the depth and angle boundary values ​​based on simulation. Furthermore, it can pre-calculate the parameter information corresponding to different target motion trajectories in the known sea area, facilitating rapid target depth classification, greatly improving computational efficiency, and is easy to implement in engineering practice. Attached Figure Description

[0023] Figure 1 The sound velocity profile used in the simulation - the Munk sound velocity profile

[0024] Figure 2Scene top view

[0025] Figure 3 Method Flowchart

[0026] Figure 4 Output of conventional beamforming of horizontal linear array at time t1

[0027] Figure 5 Target azimuth estimate changing over time curve

[0028] Figure 6 Curve showing the minimum angle of arrival of the direct wave from a linear array as a function of the sound source depth. Detailed Implementation

[0029] The present invention will now be further described in conjunction with the embodiments and accompanying drawings:

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

[0031] To verify the effectiveness of the method of this invention, a computer simulation experiment was conducted. This embodiment considers a typical deep-sea environment at a depth of 5000m, and the Munk sound velocity profile used is shown in the attached figure. Figure 1 As shown. The sound speed at the sea surface is 1550 m / s, the acoustic duct axis depth is 1100 m, the acoustic duct axis speed is 1500 m / s, the critical depth is 4430 m, and the sound speed on the seabed is 1552 m / s. The model above the sea surface represents a vacuum environment, while the seabed model represents an acoustic half-space. Specific seabed sediment parameters are: seabed sound speed is 1600 m / s, and seabed density is 1.8 g / cm³. 3 The substrate attenuation coefficient is 0.8 dB / λ.

[0032] A top view of the relative positions of the moving, regularly oriented sound source and the M=20 element linear array is attached. Figure 2 As shown, a moving sound source travels in a straight line through the forward-facing direction of the linear array, continuously radiating a single-frequency regular sound signal with a frequency of f = 750 Hz into the horizontal linear array. At time t1, the moving sound source is located on the port side of the horizontal array, at 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, at a distance r2 = 2000 m and an azimuth θ2 = 45°. The velocity of the moving sound source is 3 m / s. The depth D of the moving sound source is... soc =300m, the depth D of the receiving array rec =50m.

[0033] Combining environmental and scene information, under the assumption of far-field plane waves, the Bellhop toolbox is used to simulate the horizontal line array t1~t2, that is, the signal x(t) received at different times within the target's motion time range.

[0034] According to the design scheme provided by this invention, a flowchart of a target depth segmentation method based on the arrival angle difference of direct waves is attached. Figure 3 As shown, the features are as follows:

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

[0036] Azimuth estimate θ esti

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

[0038] Assume the horizontal linear array has M elements and the element spacing is d. Perform conventional beamforming on the received signal from the array and calculate the target azimuth estimate θ. esti The specific process is as follows:

[0039] Conventional beamforming methods are calculated using 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 Let w(θ) represent the covariance matrix of the array received signal, w(θ) represent the beam weighting vector, and H represent the transpose symbol.

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

[0043]

[0044] The azimuth estimate θ corresponds to the point where the beam output power reaches its maximum value. esti ,Right now,

[0045] θ esti =argmax(P dB (θ)). (3)

[0046] In Formula 1

[0047] The R x It is calculated using 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 the expectation.

[0050] The w(θ) is calculated using the following formula.

[0051]

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

[0053] In the example:

[0054] The procedure for estimating the direct wave angle of arrival using conventional beamforming methods on the signal x(t1) received by the horizontal line array at time t1 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 elements M = 20, the signal frequency f = 750Hz and the reference sound speed c = 1500m / s into equation (5) to calculate the beam weighting vector w(θ);

[0057] (3) The R calculated in the above two steps x Substituting w(θ) into equation (1), the output power P(θ) of the beamformer is calculated;

[0058] (4) Substitute the output power P(θ) of the beamformer into equation (2) to calculate the normalized output power P of the beamformer in decibels. dB (θ);

[0059] (5) According to formula (3), the azimuth at which the beam output power reaches its maximum value is the azimuth estimate θ. esti .

[0060] The result of normalizing the output power of conventional beamforming to decibels is shown in the attached figure. Figure 4 As shown, the estimated azimuth is 45.4°.

[0061] Sub-step 2: Calculate the minimum value θ of the target azimuth estimate. estimin .

[0062] Target azimuth estimate θ esti It is a function of time, denoted as θ esti (t), which has a minimum value when the target intersects with the UUV, denoted as θ. estimin ,Right now,

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

[0064] In the example:

[0065] For the horizontal line array t1~t2, i.e., the target movement time range, the five steps of sub-step one above are performed on the signals received at different times, i.e., the direct wave angle of arrival is estimated using conventional beamforming methods to obtain the target azimuth estimate θ at different times. esti (t).

[0066] Plot the curve of the target azimuth estimate over time θ esti (t) As attached Figure 5 As shown. The target azimuth estimate θ esti Substituting (t) into equation (6) yields θ. estimin =9.4°.

[0067] Step 2: Calculate the angular boundary θ between the water surface and the underwater target using the sound field model. crit .

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

[0069] Assume the horizontal distance between the moving target and the UUV at the intersection is R, and the horizontal array receiving depth is D. rec By combining local hydrological information of UUVs, the Bellhop toolbox was used to calculate the direct wave angle of arrival θ for targets at different depths. arr (d)

[0070] In the example:

[0071] The horizontal distance R = 1212m is known when the moving target intersects with the UUV. Using local hydrological information about the UUV, the Bellhop toolbox is used to calculate the direct wave angle of arrival θ for targets at different depths. arr (d) As attached Figure 6 As shown.

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

[0073] Angular boundary value θ crit Defined as the angle of arrival of the direct wave when the target depth d = 0m, i.e.

[0074] θ crit =θ arr (d=0m) (7)

[0075] As the target depth d increases, the depth at which the calculated direct wave angle of arrival equals the direct wave angle of arrival corresponding to the target depth d = 0m is defined as the depth boundary value D. crit That is, satisfying

[0076] θ arr (Dcrit )=θ crit (8)

[0077] In the example:

[0078] Analysis Appendix Figure 6 Combined with the angle boundary value θ in equation (7) crit The definition is that the angle of arrival of the direct wave corresponding to the target depth d = 0m is taken as the angle boundary value θ. crit , that is, θ crit =4.9°, combined with the depth boundary value D in equation (8) crit The definition is used to calculate the depth at which the angle of arrival of the direct wave is equal to the angle of arrival of the target depth d = 0m, i.e., D. crit =208m.

[0079] Step 3: Calculate the angle difference to define the target depth

[0080] Minimum value of target azimuth estimate θ estimin With the angular boundary value θ crit Compare and calculate the angle difference

[0081] Δθ=θ estimin -θ crit (9)

[0082] When Δθ > 0°, it indicates that the target depth is greater than the depth boundary value D. crit When Δθ < 0°, it indicates that the target depth is less than the depth boundary value D. crit .

[0083] In the example:

[0084] The angle difference Δθ = θ is calculated according to equation (9). estimin -θ crit =9.4° - 4.9° = 4.5°, since Δθ > 0°, it means D soc >D crit That is, the target depth is greater than the depth boundary value.

[0085] This invention is applicable not only to conformal arrays on the hull side, but also to other horizontal arrays such as towed arrays.

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

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

Claims

1. A target depth segmentation method based on the difference in arrival angle of direct waves, characterized in that... The steps are as follows: Step 1: Estimate the minimum angle of arrival of the direct wave using spectral estimation methods. θ estimin ; Step 2: Calculate the angular boundary value for target depth segmentation using the sound field model. θ crit , defined as target depth d Angle of arrival of the direct wave at =0m θ crit = θ arr ; Step 3: Calculate the minimum value of the angle of arrival of the direct wave. θ estimin and angle boundary value θ crit The angle difference is used to define the target depth; The minimum value of the angle of arrival of the direct wave θ estimin The calculation is as follows: First, the angle of arrival of the direct wave at a certain moment, i.e., the estimated target azimuth, is estimated using conventional beamforming methods. θ esti The target azimuth estimates at different times constitute a function of time, denoted as . θ esti ( t When the target intersects with a UUV, there is a minimum value. θ estimin ; The conventional beamforming method estimates the angle of arrival of the direct wave, i.e., the target azimuth estimate. θ esti Yes: The azimuth estimate is the azimuth value corresponding to the point where the beam output power reaches its maximum value. θ esti =argmax( P dB ( θ ));in: P dB ( θ The output power of a conventional beamformer is normalized to a decibel value, i.e.: P dB ( θ ) = 20lg( P ( θ ) / max( P ( θ ))), P ( θ ) represents the output power of the beamformer; Calculation of the output power of the beamformer: P ( θ )= w ( θ ) H R x w ( θ );in: R x This represents the covariance matrix of the received signal from the array. w ( θ ) represents the beam weighting vector, and H represents the transpose symbol.

2. The target depth segmentation method based on the direct wave arrival angle difference according to claim 1, characterized in that: The criterion for dividing target depth based on angle difference is as follows: Calculate ,when When, it indicates that the target depth is greater than the depth threshold. D crit ;when When, it indicates that the target depth is less than the depth threshold. D crit .

3. The target depth segmentation method based on the direct wave arrival angle difference according to claim 2, characterized in that: The depth boundary value D crit Defined as: with target depth d The increase in the angle of arrival of the direct wave and the target depth d When the angle of arrival of the direct waves corresponding to 0m is equal, the depth at which this occurs is defined as the depth boundary value. D crit ,satisfy θ arr = θ crit .

4. The target depth segmentation method based on the direct wave arrival angle difference according to claim 1, characterized in that: The angle of arrival of the direct wave θ arr The calculation involves using the Bellhop toolbox to calculate different target depths. d Corresponding direct wave angle of arrival θ arr ( d In the calculation, the horizontal distance between the moving target and the UUV at the point of intersection is known to be... R The horizontal array receiving depth is D rec Furthermore, it is necessary to combine local hydrological and environmental information of UUVs.

5. The target depth segmentation method based on the direct wave arrival angle difference according to claim 1, characterized in that: Step 1 and Step 2 can be completed simultaneously, or Step 2 can be performed first, followed by Step 1.

6. An electronic device, characterized in that, It includes a processor and a memory, wherein the processor is used to execute a computer program stored in the memory to implement the data migration step of the target depth segmentation method based on the direct wave angle of arrival difference as described in any one of claims 1 to 5.

7. A computer program product, characterized in that... It includes computer-executable instructions, which, when executed, are used to implement the target depth segmentation method based on the direct wave angle of arrival difference as described in any one of claims 1 to 5.

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