Deep-sea shadow area target rapid orientation estimation method

Abstract

The invention relates to a deep-sea shadow region target rapid orientation estimation method, which comprises the following steps: firstly, performing orientation estimation on a target signal received by a large-aperture horizontal line array by using conventional beam forming, and assuming that a sound source distance is estimated by an existing signal processing method; secondly, on the basis of the virtual source theory, the arrival pitch angles of four primary seabed reflection sound ray paths in the shadow area are calculated; based on the representation relation among the sound ray arrival pitch angle, the target physical orientation and the orientation estimation value, the target orientation estimation result is corrected, then the real orientation of the target is obtained, and the direction finding precision of the deep-sea shadow region target is improved.

Description

Technical Field

[0001] The invention belongs to the fields of ocean engineering, hydroacoustic engineering, array signal processing and sonar technology, and relates to a method for fast azimuth estimation of targets in deep sea shadow areas, which is applicable to the problem of passive direction finding of near-sea targets by a deep sea large-aperture horizontal array. Background Art

[0002] Sonar is the main means of sensing underwater target information. It can be divided into active sonar and passive sonar according to different working principles. Passive sonar uses the target radiation noise signal for passive detection, positioning, tracking and identification. It has high concealment and is an important means of detecting underwater targets.

[0003] Towed linear array sonar is a typical passive detection form. It is not only far away from the working mother ship, significantly reducing the impact of the towed platform noise; and the array size is not limited by the ship. Compared with the broadside array sonar, the towed array can improve the receiving signal-to-noise ratio by increasing the number of hydrophones and increase the array element spacing to reduce the sonar working frequency band. Based on the above advantages, towed linear array plays an important role in the field of passive detection, and direction finding accuracy is one of the important indicators of this type of sonar.

[0004] However, for the horizontal array, due to its own axial symmetry, the horizontal array cannot distinguish the azimuth and elevation angle of the incident sound wave. In the actual ocean environment, the sound signal is often reflected from multiple interfaces before being incident on the receiving hydrophone. At this time, the incident direction of the sound wave has different directional components in the horizontal and vertical planes of the horizontal array. Therefore, the angle value obtained by the azimuth estimation is not the actual physical azimuth of the target.

[0005] In a deep-sea environment, when the sound source and the receiving array are both located at a shallow depth, the sound field can be spatially divided into a direct zone, an acoustic shadow zone, and a convergence zone. For the direct sound lines in the direct zone and the reverse sound lines in the convergence zone, the pitch angles of the sound lines are generally small; while the sound field in the acoustic shadow zone is composed of sound lines after multiple reflections from the sea surface and the seabed, and because the ocean is deep, the pitch angles of the sound lines are relatively large. When the receiving towed array is located within the acoustic shadow zone, the large-angle incident sound line will cause the target azimuth estimation result of the towed array to seriously deviate from the target's true physical azimuth, resulting in a direction-finding error. Since this direction-finding error is related to the pitch angle of the sound line arrival, when the distance of the sound source relative to the towed array is known, the pitch angle of the incident sound line can be calculated, and combined with its geometric relationship, the pitch angle of the sound line arrival can be used to correct the target azimuth. Based on the above background, the present invention proposes a method for fast physical azimuth estimation of deep-sea shadow zone targets to improve the direction-finding accuracy of deep-sea towed arrays. Summary of the invention

[0006] Technical issues to be solved

[0007] In order to avoid the shortcomings of the prior art, the present invention proposes a method for fast azimuth estimation of targets in deep sea shadow areas.

[0008] Technical Solution

[0009] A method for fast azimuth estimation of a target in a deep sea shadow area, characterized by the following steps:

[0010] Step 1: Use the conventional beamforming method to estimate the azimuth of the target signal received by the large aperture horizontal linear array, and obtain P(θ) to represent the output power spectrum of the beamformer. The azimuth value corresponding to the maximum output power is the azimuth estimate value.

[0011] Step 2: Under the condition that the depth and distance of the sound source are known, the pitch angles of the four primary seabed reflected sound rays in the shadow area are calculated according to the virtual source theory, and the pitch angles of the four sound rays are obtained, which are the pitch angles of the seabed receiving path BR The elevation angle of the BSR receiving path from the seabed to the sea surface The elevation angle of the SBR receiving path from the sea surface to the sea bottom The elevation angle of the SBSR receiving path from sea surface to sea bottom to sea surface

[0012] Step 3: Take the absolute value of the pitch angle of the four sound rays and then take the average to get

[0013]

[0014] Step 4: Estimate the direction based on the direction in step 1 The physical position of the target can be quickly estimated by the following calculation:

[0015]

[0016] The output power spectrum of the beamformer is P(θ)=w(θ) H R x w(θ), where: P(θ) represents the output power spectrum of the beamformer, R x represents the covariance matrix of the array receiving signal, w(θ) represents the beam weight vector, H represents the conjugate transposed sign, θ is the beam scanning azimuth, and the scanning angle range is 0-180°.

[0017] The covariance matrix R of the array received signal x =E[x(t)x(t) H ], where x(t) is the sound signal received by the horizontal array, and E[.] represents the expectation.

[0018] The beam weight vector w(θ)=[1,e iωdcosθ / c,e iω2dcosθ / c ,…,e iω(N-1)dcosθ / c ] / N, where ω is the angular frequency of the radiation frequency f, ω=2πf, c is the reference sound velocity, defined as the sound velocity value at the horizontal array receiving depth; d is the array element spacing, and N is the number of array elements.

[0019] The radiation frequency f is a single-frequency signal, which is suitable for broadband and narrowband receiving signals.

[0020] The pitch angles of the four sound rays are calculated as follows:

[0021]

[0022] Where: H is the sea depth, z s is the sound source depth, z r is the receiving depth, R is the sound source distance, which is defined as the horizontal distance between the first array element and the sound source, and tan -1 Represents the inverse tangent function.

[0023] A method for using the method for rapid azimuth estimation of targets in deep sea shadow areas is characterized in that the receiver is located near the sea surface in the deep sea acoustic shadow area. For a typical deep sea Munk environment, the receiving distance range is 6 to 25 km, and the receiving depth range is 0 to 1000 m.

[0024] An electronic device, characterized in that it includes a processor and a memory, wherein the processor is used to implement the steps of data migration of the method for rapid azimuth estimation of deep-sea shadow targets when executing a computer program stored in the memory.

[0025] A readable storage medium, characterized in that a computer program is stored on the readable storage medium, and when the computer program is executed by a processor, the steps of data migration of the method for rapid azimuth estimation of deep-sea shadow targets are implemented.

[0026] A computer program product, characterized by comprising computer executable instructions, which are used to implement the method for rapid azimuth estimation of deep-sea shadow area targets when executed.

[0027] Beneficial Effects

[0028] The present invention proposes a method for fast azimuth estimation of deep-sea shadow zone targets. Firstly, conventional beamforming is used to estimate the azimuth of target signals received by a large-aperture horizontal line array, and it is assumed that the sound source distance has been estimated by an existing signal processing method. Secondly, based on the virtual source theory, the arrival elevation angles of four primary seabed reflection sound line paths in the shadow zone are calculated. Based on the representation relationship between the arrival elevation angles of the sound lines, the physical azimuth of the target and the azimuth estimation value, the target azimuth estimation result is corrected to obtain the true azimuth of the target, thereby improving the direction finding accuracy of deep-sea shadow zone targets.

[0029] The beneficial effects are reflected in:

[0030] (1) The formula is concise and its physical meaning is clear; the true position of the target can be calculated based on the formula;

[0031] (2) The proposed method does not rely on sound field modeling, which greatly saves the amount of calculation and is easy to implement in engineering;

[0032] (3) The basic principle and implementation scheme of the method proposed in the present invention have been verified by computer numerical simulation. The results show that in a typical deep-sea Munk environment, the method proposed in the present invention can effectively estimate the physical orientation of near-sea surface targets. In the typical implementation case given, the method proposed in the present invention can reduce the orientation estimation error from 7.1° to 0.4° compared with the conventional method. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 : Schematic diagram of the sound speed profile of the simulation scenario.

[0034] Figure 2 : Top view of the sound source-horizontal array geometric position.

[0035] Figure 3 : Characteristic sound line propagation trajectory of deep-sea acoustic shadow zone obtained using the ray model (source depth 200m, receiving depth 200m, source distance 20km).

[0036] Figure 4 : Comparison results of theoretical and modeling calculations of sound arrival pitch angles at different sound source depths and distances in the acoustic shadow zone (sea depth 5000m, receiving depth 200m).

[0037] (a) BR arrival angle theoretical calculation results

[0038] (b) BR arrival angle sound field simulation results

[0039] (c) Theoretical calculation results of BSR arrival angle

[0040] (d) BSR arrival angle sound field simulation results

[0041] Figure 5 : Comparison of sound source direction estimation results under different sound source distances and directions (sound source depth 200m, receiving depth 200m).

[0042] (a) Sound source direction 30°

[0043] (b) Sound source direction 45°

[0044] (c) Sound source direction 60°

[0045] (d) Sound source direction 75° DETAILED DESCRIPTION

[0046] The present invention will now be further described with reference to the embodiments and the accompanying drawings:

[0047] The technical solution adopted by the present invention to solve its technical problem is:

[0048] 1. Deep sea environment configuration:

[0049] In order to verify the effectiveness of the method of the present invention, a simulation experiment was performed using a computer. This embodiment considers a typical deep sea environment, Munk sound velocity profile, and a sea depth of 5000m. Figure 1 As shown. The sea surface sound speed is 1550m / s, the channel axis depth is 1100m, the channel axis sound speed is 1500m / s, the critical depth is 4430m, and the seabed sound speed is 1552m / s. The seabed is modeled as a uniform infinite half space, the seabed sound speed is 1600m / s, and the density is 1.6g / m 3 , attenuation coefficient 0.2dB / λ.

[0050] 2. A method for fast azimuth estimation of a target in a deep sea shadow area, characterized by comprising the following steps:

[0051] Step 1: For a large aperture horizontal uniform linear array, assume that the number of array elements is N and the spacing is d; assume that the sound source is a point source that radiates a single-frequency signal with a frequency of f. The sound source distance is defined as the horizontal distance between the first array element of the horizontal array and the sound source, denoted as R. The angle formed by the line connecting the sound source and the first array element and the horizontal array axis is defined as the target azimuth, denoted as θ.

[0052] In the embodiment: for a large aperture horizontal uniform linear array, the number of array elements is N = 51, the array element spacing is d = 4m, and the array receiving depth is z r =200m; Assume that the sound source is a point source, the radiation frequency is a single-frequency signal of f=150Hz, and the depth of the sound source is z s = 100m; the sound source distance is defined as the horizontal distance between the first array element of the horizontal array and the sound source, denoted as R, and the angle formed by the line connecting the sound source and the first array element and the axis of the horizontal array is defined as the target azimuth, denoted as θ. The top view of the geometric position of the sound source relative to the horizontal array is shown in the attached figure. Figure 2 As shown, at time t, the target is located at R = 20 km, θ = 40° in the horizontal array.

[0053] The Bellhop ray model is used to simulate the propagation trajectory of the characteristic sound line received by the horizontal array head element, as shown in the attached figure. Figure 3As shown in the figure, the sound field in the deep sea acoustic shadow area is mainly contributed by the primary seabed reflection wave. The secondary and higher seabed reflection waves have a large energy attenuation due to the large number of interface reflections, so their influence on the sound field is negligible. The horizontal emission of the sound line in the vertical plane is defined as 0°, the emission angle pointing to the sea surface is negative, and the emission angle pointing to the seabed is positive. The four characteristic sound lines can be divided into two categories according to the positive and negative arrival angles. The arrival angles of the sound lines in the same category can be considered to be approximately equal.

[0054] Step 2: Perform conventional beamforming on the array received signal to obtain the target's azimuth estimate relative to the horizontal array The specific process is as follows:

[0055] The conventional beamforming method can be calculated by the following formula:

[0056] P(θ)=w(θ) H R x w(θ) (1)

[0057] Where P(θ) is the output power of the beamformer, R x represents the covariance matrix of the array received signal, w(θ) represents the beam weight vector, and H represents the transposed symbol. The azimuth corresponding to the maximum beam output power is the azimuth estimate.

[0058] The R x It is calculated by the following formula:

[0059] R x =E[x(t)x(t) H ] (2)

[0060] Among them, x(t) is the sound signal received by the horizontal array, and E[.] represents the expectation.

[0061] The w(θ) is calculated by the following formula,

[0062] w(θ)=[1,e iωdcosθ / c , e iω2dcosθ / c ,…,e iω(N-1)dcosθ / c ] / N (3)

[0063] Wherein, ω is the angular frequency, ω=2πf, c is the reference sound velocity, which is defined as the sound velocity value at the horizontal array receiving depth, d is the array element spacing, and N is the number of array elements.

[0064] In the embodiment: ω is the angular frequency, ω=2πf, f=150 Hz, the sound velocity c is defined as the sound velocity value at the horizontal array receiving depth, c=1527.6 m / s, d=4 m, N=51, wherein 0°≤θ≤180°.

[0065] From this, the conventional beam output diagram of the horizontal array can be calculated. It can be seen that the maximum azimuth of the target azimuth response is at The deviation from the target's actual physical position is θ=40°.

[0066] Step 3: Assuming that the depth and distance of the sound source are known, the arrival angles of the four primary seabed reflected sound rays in the shadow area can be calculated according to the virtual source theory. These four sound rays are the seabed receiving path (BR), the seabed-sea surface receiving path (BSR), the sea surface-seabed receiving path (SBR), and the sea surface-seabed-sea surface receiving path (SBSR). The specific calculation formula is as follows:

[0067]

[0068] In the formula denote the arrival pitch angles of BR, SBR, BSR and SBSR paths, respectively, H is the sea depth, z s is the sound source depth, z r is the receiving depth, R is the distance from the sound source, tan -1 Represents the inverse tangent function.

[0069] In the embodiment: denote the arrival pitch angles of BR, SBR, BSR and SBSR paths, respectively. The ocean depth is H = 5000 m and the sound source depth is z s =100m, receiving depth z r =200m, sound source distance R = 20km, tan -1 represents the inverse tangent function. By calculation, we get

[0070] The Bellhop ray model is used to model the sound field, simulate the distribution law of the pitch angle of sound rays at different sound source depths and distances in the sound shadow area, and compare it with the theoretical calculation results. The results are shown in the attached figure. Figure 5 It can be found that the theoretical calculation results are consistent with the sound field modeling results. Compared with the sound source depth, the arrival pitch angle is more sensitive to the change of the sound source distance; as the distance increases, the absolute values ​​of the arrival angles of the two types of sound rays gradually decrease.

[0071] Step 4: Take the absolute values ​​of the above four sound ray arrival angles and then take the average to get

[0072]

[0073] In the embodiment: the four sound rays arriving at the pitch angles obtained in step 3 are brought into the calculation to obtain

[0074] Step 5: Use formula (5) to calculate the average pitch angle of the sound ray at the current target distance. Combined with the target azimuth estimate, the physical azimuth of the target can be quickly estimated. The specific calculation formula is as follows:

[0075]

[0076] In the embodiment: the sound line reaches the average pitch angle and target position estimate Substituting this into the equation, we can get the target azimuth estimated by the present invention as θ≈40.4°, which is slightly lower than the azimuth estimated by the conventional beamforming method. The azimuth estimation error of the method proposed in the present invention is reduced from 7.1° to 0.4°.

[0077] The receiver of the present invention is located near the sea surface in the deep sea acoustic shadow area. For a typical deep sea Munk environment, the receiving distance ranges from 6 to 25 km and the receiving depth ranges from 0 to 1000 m.

[0078] Figure 6 shows the comparison of the sound source azimuth estimation results of the method proposed in the present invention and the conventional beamforming method at different sound source distances and azimuths. (a) Sound source azimuth 30°; (b) Sound source azimuth 45°; (c) Sound source azimuth 60°; (d) Sound source azimuth 75°. Sound source depth 100m, receiving depth 200m. It can be seen that the proposed method has a high azimuth estimation accuracy at different sound source positions, which also illustrates the effectiveness of the method proposed in the present invention.

[0079] The present invention is not only applicable to conventional beamforming methods and horizontal linear arrays, but also to other beamforming methods and non-uniform linear arrays.

Claims

1. A method for fast azimuth estimation of targets in deep sea shadow areas, characterized in that Here are the steps: Step 1: Use the conventional beamforming method to estimate the azimuth of the target signal received by the large aperture horizontal linear array, and obtain P(θ) to represent the output power spectrum of the beamformer. The azimuth value corresponding to the maximum output power is the azimuth estimate value. Step 2: Under the condition that the depth and distance of the sound source are known, the pitch angles of the four primary seabed reflected sound rays in the shadow area are calculated according to the virtual source theory, and the pitch angles of the four sound rays are obtained, which are the pitch angles of the seabed receiving path BR The elevation angle of the BSR receiving path from the seabed to the sea surface The elevation angle of the SBR receiving path from the sea surface to the sea bottom The elevation angle of the SBSR receiving path from sea surface to sea bottom to sea surface Step 3: Take the absolute value of the pitch angle of the four sound rays and then take the average to get Step 4: Estimate the direction based on the direction in step 1 The physical position of the target can be quickly estimated by the following calculation:

2. The method for rapid azimuth estimation of a target in a deep sea shadow area according to claim 1, characterized in that: The output power spectrum of the beamformer is P(θ)=w(θ) H R x w(θ), where: P(θ) represents the output power spectrum of the beamformer, R x represents the covariance matrix of the array receiving signal, w(θ) represents the beam weight vector, H represents the conjugate transposed sign, θ is the beam scanning azimuth, and the scanning angle range is 0-180°.

3. The method for rapid azimuth estimation of a target in a deep sea shadow area according to claim 1, characterized in that: The covariance matrix R of the array received signal x =E[x(t)x(t) H ], where x(t) is the sound signal received by the horizontal array, and E[.] represents the expectation.

4. The method for rapid azimuth estimation of a target in a deep sea shadow area according to claim 1, characterized in that: The beam weight vector w(θ)=[1,e iωdcosθ / c ,e iω2dcosθ / c ,…,e iω(N-1)dcosθ / c ] / N, where ω is the angular frequency of the radiation frequency f, ω=2πf, c is the reference sound velocity, defined as the sound velocity value at the horizontal array receiving depth; d is the array element spacing, and N is the number of array elements.

5. The method for rapid azimuth estimation of a target in a deep sea shadow area according to claim 1, characterized in that: The radiation frequency f is a single-frequency signal, which is suitable for broadband and narrowband receiving signals.

6. The method for rapid azimuth estimation of a target in a deep sea shadow area according to claim 1, characterized in that: The pitch angles of the four sound rays are calculated as follows: Where: H is the sea depth, z s is the sound source depth, z r is the receiving depth, R is the sound source distance, which is defined as the horizontal distance between the first array element and the sound source, and tan -1 Represents the inverse tangent function.

7. A method for using the method for rapid azimuth estimation of deep sea shadow area targets according to claims 1 to 6, characterized in that The receiving device is located near the sea surface in the deep sea acoustic shadow area. For a typical deep sea Munk environment, the receiving distance ranges from 6 to 25 km and the receiving depth ranges from 0 to 1000 m.

8. An electronic device, characterized in that: The method comprises a processor and a memory, wherein the processor is used to implement the data migration step of the method for rapid azimuth estimation of a deep-sea shadow target as claimed in any one of claims 1 to 6 when executing a computer program stored in the memory.

9. A readable storage medium, characterized in that: The readable storage medium stores a computer program, which, when executed by a processor, implements the steps of data migration of the method for rapid azimuth estimation of a deep-sea shadow target as claimed in any one of claims 1 to 6.

10. A computer program product, characterized in that It comprises computer executable instructions, which, when executed, are used to implement the method for rapid orientation estimation of a deep-sea shadow target as claimed in any one of claims 1 to 6.

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