Beam-controlled emission pitch angle design method for continuous tracking of upward-looking active target

Abstract

The invention provides a beam-controlled emission pitch angle design method for continuous tracking of a look-up active target, a multi-path arrival structure for receiving near sea surface target receiving sound rays including direct sound and sea surface primary reflection sound under a deep sea look-up active detection background is mainly researched, and an internal mechanism of correlation between a pitch angle and target distance change is analyzed. Aiming at the specific background of deep-sea look-up active detection, firstly, the research basis of deep-sea large-depth sound propagation characteristics and sound field correlation is fully utilized, and target information carried by an excavated deep-sea sound field echo space-time multi-path arrival structure is utilized, so that an emission angle is firstly changed to reach an expected distance emission beam control angle of a next emission period; therefore, more accurate positioning of the target is realized, and continuous tracking of the target is realized by circulating the process.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater acoustic detection and tracking recognition, and mainly relates to a beam control emission elevation angle design method for continuous tracking of upward-looking active targets. Background Technique

[0002] The active detection technology of underwater acoustic targets refers to the signal processing technology that realizes the detection, tracking, positioning and recognition of underwater acoustic targets within a certain range by receiving the scattered echoes of underwater acoustic targets. On the one hand, with the rapid development of modern ship engineering technology, the echo intensity of ships in the traditional working frequency band of active detection has decreased by 5-15 dB [1] , on the other hand, the increasing frequency of human ocean activities and submarine geological movements has led to a significant increase in ocean ambient noise, especially low-frequency noise [2,3] . At the same time, the characteristics of spatio-temporal random fluctuations, environmental uncertainty, channel uncertainty, and parameter uncertainty caused by complex ocean environments [4] and the uncertainty of the number of target types, the unknown target motion model, the uncertainty of measurement-target association, and the lack of robustness of tracking algorithms, etc., jointly cause the instability and inaccuracy of underwater acoustic target tracking. Coupled with poor underwater acoustic communication quality, information transmission being limited by bandwidth, and interference from acoustic propagation multipath effects, etc., it leads to untimely target information interaction and information loss. All of the above factors will seriously affect the performance of underwater acoustic target tracking [5] .

[0003] Currently, underwater acoustic target tracking mainly relies on passive tracking. The observed values and state variables have a non-linear relationship. The mainstream methods are all developed based on filtering methods such as the Extended Kalman Filter (EKF), second-order filter, iterative filter, Particle Filter (PF), and Shifted Rayleigh Filter (SRF), etc. [6-8] , and have relatively high requirements for signal-to-noise ratio. For example, EKF transforms the non-linear solution into a linear estimate through a spatial transformation matrix to achieve underwater acoustic target tracking under weak interference. CKF [9] transforms the non-linear filtering estimate into an integral problem of the product of a non-linear function and a Gaussian probability density function to solve the underwater high-dimensional non-linear problem and reduce the calculation amount. The PF

[10] algorithm uses a non-parametric sequential Monte Carlo simulation method to implement recursive Bayesian filtering. Further, some scholars also thought of combining methods such as KF, EKF, UKF, and PF with the Interacting Multiple Model (IMM)

[11] To improve the stability of target tracking. From the development from EKF to CKF, PF and subsequent progress, it can be seen that scholars have mainly focused on researching tracking methods that are not limited by linearization errors or Gaussian noise assumptions and are applicable to various state transitions or measurement models in various environments. However, the research on this "predictive interception type" that uses the known target information to change the emission parameters to achieve more accurate tracking and positioning of the target in the next emission cycle is still blank.

[0004] [1] Huang Haining, Li Yu. Research Status and Prospect of Underwater Acoustic Target Detection Technology [J]. Bulletin of the Chinese Academy of Sciences, 2019, 34(03): 264-271. DOI: 10.16418 / j.issn.1000-3045.2019.03.003.

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[0007] [4] Yang Shi'e. Principles of Underwater Acoustic Propagation. Harbin: Harbin Engineering University Press, 2007.

[0008] [5] Liu Meiqin, Han Xueyan, Zhang Senlin, et al. Research Status and Prospect of Target Tracking Technology Based on Underwater Sensor Networks [J]. Acta Automatica Sinica, 2021, 47(2): 235-251.

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[0010] [7] YI Wei, FU Lingzhi, F, et al. Particle filtering - based track - before - detect method for passive array sonar systems[J]. Signal Processing, 2019, 165: 303 - 314.

[0011] [8] Radhakrishnan R, Bhaumik S, Tomar N K. Gaussian sum shifted Rayleigh filter for underwater bearings - only target tracking problems[J]. IEEE Journal of Oceanic Engineering, 2019, 44(2): 492 - 501.

[0012] [9] Guo Ge, Wang Xingkai, Xu Huipu. Review of underwater target detection, recognition and tracking based on sonar images[J]. Control and Decision, 2018, 33(5): 906 - 922.

[0013]

[10] Ahwiadi M, Wang W. An adaptive particle filter technique for system state estimation and prognosis[J]. IEEE Transactions on Instrumentation and Measurement, 2020, 69(9): 6756 - 6765.

[0014]

[11] LIANG H, KANG F. Tracking UUV based on interacting multiple model unscented particle filter with multi - sensor information fusion[J]. Optik, 2015, 126(24): 5067 - 5073. Summary of the Invention

[0015] The object of the present invention is to overcome the deficiencies existing in the prior art, and to provide a beam - controlled launch elevation angle design method for continuous tracking of upward - looking active targets.

[0016] The object of the present invention is achieved by the following technical solutions. A beam - controlled launch elevation angle design method for continuous tracking of upward - looking active targets, the method comprising the following steps:

[0017] Step (1): Based on the input parameters, calculate the target distance at a certain moment according to the pitch angle - distance matching method.

[0018] Step (2): Based on the input parameters, calculate the radial velocity of the target movement at this moment according to the Doppler frequency shift.

[0019] Step (3): Calculate the movement distance of the target in one emission cycle.

[0020] Step (4): Predict the target distance at the next cycle of emission.

[0021] Step (5): According to the corresponding relationship between the pitch angle and the distance, calculate the pitch angle corresponding to the distance at the next cycle of emission.

[0022] Through the above steps, after discovering the target at any moment and obtaining the distance and speed information, by controlling the active emission angle, more accurate positioning of the target can be achieved. By cycling through the above steps, continuous tracking can be realized.

[0023] The beneficial effects of the present invention are as follows: The present invention focuses on studying the multi - path arrival structure of the received sound rays of near - sea surface targets including direct sound and sea - surface primary reflected sound under the background of deep - sea upward - looking active detection, and analyzes the internal mechanism of the correlation between the pitch angle and the target distance change. For the specific background of deep - sea upward - looking active detection, first, make full use of the research basis of the deep - sea large - depth sound propagation characteristics and the sound field correlation, and use the target information carried by the spatio - temporal multi - path arrival structure of the deep - sea sound field echo. First, change the emission angle to reach the expected distance emission beam - control angle at the next emission cycle, so as to achieve more accurate positioning of the target. By cycling through the above process, continuous tracking of the target can be realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following - described drawings are only some embodiments of the present invention. For those skilled in the art or ordinary technicians, without creative efforts, other drawings can be obtained based on these drawings.

[0025] Figure 1 It is a flowchart for realizing continuous tracking of the target by changing the beam - control emission pitch angle under the background of deep - sea upward - looking active detection.

[0026] Figure 2 It is a schematic diagram of the geometric propagation of sound rays.

[0027] Figure 3 It is the relationship between the pitch angles of the direct sound and the sea - surface primary reflected sound obtained by simulation and the change of the target distance.

[0028] Figure 4 Top view of the relative position relationship.

[0029] Figure 5 Schematic diagram of continuously tracking a target by changing the numerical control emission angle. Specific implementation manner

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] As Figure 1 shown, the present invention provides a flowchart for continuously tracking a target by changing the elevation angle of beam control in the context of deep-sea upward-looking active detection. First, using the environmental parameters such as the sound speed and sea depth of a certain sea area obtained by actual measurement, and the equipment parameters such as the emission and reception time and period, on the one hand, calculate the distance between the target and the array at a certain moment according to the method of matching the elevation angle - distance, and on the other hand, obtain the radial velocity of the target movement at this moment according to the Doppler frequency shift; then calculate the distance of the target at the next moment based on this information; then obtain the angle that needs to be changed for the next cycle of emission according to the corresponding relationship between the elevation angle and the distance, and use the time delay difference of multiple emission elements to achieve the change of the beam control angle. Finally, repeating these steps can achieve continuous tracking of the target.

[0032] The method includes the following steps:

[0033] (1) Calculate the target distance at a certain moment based on the elevation angle - distance matching method

[0034] Assume that the position of the sound source near the sea surface is S(r, z s ), the position of the virtual source is S′(r, -z s ), the position of the receiving hydrophone is P(0, z r ), the sound source makes a uniform linear motion with a speed of v, and the closest distance r between the sound source and the vertical array min , the sailing distance is v(t - t0), where t is a certain observation moment and t0 is the moment when the horizontal distance between the sound source and the vertical array is the closest. Then the distance between the vertical hydrophone array and the target at time t is:

[0035]

[0036] The direct sound elevation angle of the hydrophone array receiving the target radiation sound signal at time t is

[0037]

[0038] The elevation angle of the sea surface's first - order reflected sound of the target - radiated acoustic signal received by the hydrophone array at time t is

[0039]

[0040] As can be seen from Equations (2) and (3), for a vertical array deployed near the seabed in deep - sea, the depth of the sound source near the sea surface in deep - sea is a small quantity compared to the depth of the array at the seabed. At this time, the direct sound wave and the sea - surface's first - order reflected sound wave can be regarded as approximately equal. At this time, the target distance r at a certain moment can be obtained by using the elevation angle estimated by the matched vertical array.

[0041] Figure 2 The geometric propagation schematic diagram of the sound ray is given. In the deep - sea reliable sound path mode, for a deep - sea shallow - layer sound source, the energy received by a large - depth acoustic receiver mainly comes from the superposition of the direct sound and the sea - surface reflected sound, which is called Lloyd mirror interference.

[0042] Figure 3 The relationship between the elevation angles of the direct sound and the sea - surface's first - order reflected sound varying with the target distance obtained by simulation is given. It can be seen that when the sea depth is determined, there is a one - to - one correspondence between the elevation angles of the direct sound and the sea - surface's first - order reflected sound and the target distance, that is, the target distance can be obtained from the arrival elevation angle, and vice versa.

[0043] (2) Calculate the radial velocity of the target's movement at this moment using the Doppler shift

[0044] In water, the Doppler - shift formula can be expressed as:

[0045]

[0046] where f is the original frequency of transmission; f′ is the received frequency; v is the propagation speed of sound waves in water; v g is the velocity of the target relative to the water.

[0047] Then the target velocity v g can be solved as:

[0048]

[0049] And it can be judged whether the target is in a state of moving away from or approaching the array according to the magnitudes of the frequencies f and f′.

[0050] (3) Calculate the moving distance of the target in one transmission period

[0051] Given that the transmission period of the transmission system is T, then the distance s that the target moves in one transmission period (assuming the target is in uniform linear motion) is T = v g ·T.

[0052] (4) Predict the target distance at the time of launch in the next cycle

[0053] Based on the horizontal distance of the target relative to the array at a certain moment obtained in step (1) and the distance the target moves within one launch cycle obtained in step (3), and combined with the information on whether the target is moving away from or towards the array in step (2), the horizontal distance of the target relative to the array at the time of launch in the next cycle can be obtained:

[0054] s next = s ± s T (6)

[0055] Where, if f < f′ then s next = s - s T , conversely, s next = s + s T .

[0056] (5) Calculate the elevation angle corresponding to the distance at the time of launch in the next cycle

[0057] According to step (1), it can be known that the elevation angle corresponds one-to-one with the target distance. Thus, the elevation angle θ2 corresponding to the distance at the time of launch in the next cycle can be obtained. If there are multiple transmitting elements in the active transmission system, different time delays can be applied to each element to form sound beams with different angles. This beam angle can be calculated by the following formula:

[0058]

[0059] Where, c is the speed of sound, Δt is the time delay between adjacent elements, and d is the element spacing.

[0060] Figure 4 shows a top view of the relative position relationship, Figure 5 shows a schematic diagram of continuously tracking the target by changing the numerically controlled transmission angle. Through the above steps, after detecting the target and obtaining the distance and speed information at any moment, more accurate positioning of the target can be achieved by controlling the active transmission angle. By looping through the above process, continuous tracking can be realized.

[0061] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claimed rights.

Claims

1. A method for designing the elevation angle of beam control emission for continuous tracking of an upward-looking active target, characterized in that: The method includes the following steps: Step (1), based on the input parameters, calculate the target distance at a certain moment according to the pitch angle - distance matching method; Step (2), based on the input parameters, calculate the radial velocity of the target movement at this moment according to the Doppler frequency shift; Step (3), calculate the movement distance of the target in one emission period; Step (4), predict the target distance at the next emission period; Step (5), according to the corresponding relationship between the pitch angle and the distance, calculate the pitch angle corresponding to the distance at the next emission period; Through the above steps, after discovering the target at any moment and obtaining the distance and velocity information, by controlling the active emission angle, more accurate positioning of the target can be achieved. By looping through the above steps, continuous tracking can be realized.

2. The elevation angle design method of beam control emission for upward-looking active target continuous tracking according to claim 1, characterized in that: In the said step (1) or (2), the input parameters include the sound speed, sea depth, emission time, reception time, and emission period.

3. The elevation angle design method of beam control emission for continuously tracking an upward-looking active target according to claim 2, wherein: In the said step (1), Suppose the position of the sound source near the sea surface is S(r, z s ), the position of the virtual source is S′(r, -z s ), the position of the receiving hydrophone is P(0, z r ), the sound source moves in a uniform straight line with a speed of v, and the closest distance r between the sound source and the vertical array min , the sailing distance is v(t - t0), where t is a certain observation time and t0 is the time when the horizontal distance between the sound source and the vertical array is the closest; then the distance between the vertical hydrophone array and the target at time t is: The direct - wave pitch angle of the target - radiated acoustic signal received by the hydrophone array at time t is The sea - surface first - reflection pitch angle of the target - radiated acoustic signal received by the hydrophone array at time t is It can be seen from Equation (2) and Equation (3) that for a vertical array deployed near the seabed in deep sea, the source depth near the sea surface in deep sea is a small quantity compared with the array depth at the seabed. At this time, the direct wave and the sea - surface first - reflection wave are regarded as approximately equal; at this time, the target distance r at a certain moment can be obtained by using the pitch angle estimated by the matched vertical array.

4. The elevation angle design method of beam control emission for continuous tracking of upward-looking active targets according to claim 3, characterized in that: In the said step (2), In water, the Doppler frequency - shift formula is expressed as: Among them, f is the original frequency of emission; f' is the received frequency; v is the propagation speed of sound waves in water; v g is the speed of the target relative to the water; Then the target speed v can be calculated g : And the state of whether the target is moving away from or approaching the array relative to the array can be judged by the magnitudes of the frequencies f and f'.

5. The elevation angle design method of beam control emission for upward-looking active target continuous tracking according to claim 4, wherein: In the said step (3), The emission period of the known emission system is T. Assuming that the target is moving in a uniform straight line, the distance traveled by the target within one emission period is s T = v g ·T.

6. The elevation angle design method of beam control emission for upward-looking active target continuous tracking according to claim 5, characterized in that: In the said step (4), According to the horizontal distance of the target relative to the array at a certain moment obtained in step (1) and the distance that the target moves within one emission period obtained in step (3), and combined with the information of whether the target is moving away from or approaching the array in step (2), the horizontal distance of the target relative to the array at the next emission period can be obtained: s next = s ± s T (6) Wherein, if f < f', then s next = s - s T , and vice versa, s next = s + s T .

7. The pitch angle design method for beam control emission for continuous tracking of upward-looking active targets according to claim 6, characterized in that: In the said step (5), According to step (1), the pitch angle corresponds one-to-one with the target distance, that is, the pitch angle θ2 corresponding to the distance at the next cycle of launch can be obtained. When there are multiple transmitting elements in the active transmitting system, different time delays can be applied to each element to form sound beams with different angles; the angle of this beam is calculated by the following formula: Where c is the sound speed, Δt is the time delay between adjacent array elements, and d is the array - element spacing.

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