A method for locating a near-field target at sea based on array shape estimation

Abstract

The application discloses a sea near-field target positioning method based on array shape estimation, and belongs to the technical field of sea target positioning. The application solves the problem of low positioning precision of the existing method based on towed array shape estimation for near-field target positioning without additional information. The method comprises the following steps: in step one, the positions of hydrophones in the towed array at the current time are calculated according to the signals received by the hydrophones; in step two, the array shape of the towed array at the current time is obtained according to the mechanical model of the towed array and the towed cable and the positions of the hydrophones; in step three, the target direction is obtained through focused beam forming according to the array shape of the towed array; and the position and speed of the target at the current time are estimated according to the target direction and Doppler information. The method can be applied to the field of sea target positioning.

Description

Technical Field

[0001] This invention belongs to the field of maritime target positioning technology, specifically relating to a method for locating near-field maritime targets based on formation estimation. Background Technology

[0002] Maritime target localization is of great practical significance. Traditional methods for maritime target localization mainly employ radio positioning, electromagnetic ranging, and optical positioning. In recent years, to meet the mission requirements of maritime vehicles, these vehicles often carry relatively expensive and complex towed arrays. After receiving commands, maritime vehicles perform maneuvers and turns; improper operation can lead to tangling or breakage of the towed array, resulting in serious losses. Simultaneously, to enhance detection efficiency, the length of towed arrays is continuously increasing, significantly increasing the difficulty of obstacle avoidance for vehicles. Accurate localization of targets entering the near field is a crucial step in achieving obstacle avoidance for maritime vehicles. In recent years, near-field target localization technology based on towed array formation estimation has made some progress; however, existing methods, without utilizing additional information, still cannot provide real-time and accurate estimation of the towed array formation.

[0003] Therefore, without utilizing additional information, the existing methods based on towed array formation estimation still have low accuracy in locating near-field targets, making it essential to propose a new near-field target localization method. Summary of the Invention

[0004] The purpose of this invention is to address the problem of low accuracy in near-field target localization using existing methods based on towed array formation estimation without utilizing additional information, and to propose a near-field target localization method based on array formation estimation at sea.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for locating near-field targets at sea based on formation estimation, the method specifically includes the following steps:

[0007] Step 1: Calculate the position of each hydrophone in the towed array at the current moment based on the signals received by each hydrophone at the current moment.

[0008] Step 2: Based on the mechanical model of the towed array and tow cable at the current moment and the position of each hydrophone, obtain the formation of the towed array at the current moment;

[0009] Step 3: Focus beamforming is performed based on the towed array configuration to obtain the target's azimuth; then, the target's position and velocity at the current moment are estimated based on the target's azimuth and Doppler information.

[0010] Furthermore, the towed array is an array composed of M isotropic hydrophones;

[0011] In the linear array state, the towed array is a uniform linear array. According to the distance between each hydrophone and the noise source of the tow body in the linear array state, each hydrophone is sequentially numbered as the 1st hydrophone, the 2nd hydrophone, ..., the Mth hydrophone. That is, the hydrophone with the smallest distance from the noise source of the tow body is numbered as the 1st hydrophone, and the hydrophone with the largest distance from the noise source of the tow body is numbered as the Mth hydrophone. The 1st hydrophone is used as the reference hydrophone.

[0012] Furthermore, the signal received by the towed array is:

[0013] x(t)=A·S(t)+N(t) (1)

[0014] Where x(t) is the signal vector received by the towed array at the current moment, and the dimension of x(t) is M×1, x(t)=[x1(t),x2(t),…,x M [(t)],x1(t),x2(t),…,x M (t) is the signal received by the 1st, 2nd, ..., Mth hydrophone in the towed array at the current moment, S(t) is the tow body noise source signal vector received by the towed array at the current moment, and the dimension of S(t) is M×1, N(t) is the environmental additive noise signal vector received by the towed array at the current moment, and the dimension of N(t) is M×1, and A is the M-dimensional array manifold vector;

[0015] The signal strength received by each hydrophone in the towed array is:

[0016]

[0017] Where, p m (t) represents the signal strength received by the m-th hydrophone in the towed array, where n m (t) represents the additive environmental noise signal received by the m-th hydrophone in the towed array, μ m Let s(t-μ) be the time difference between the towed body noise source signal and the m-th hydrophone. m Let be the noise source signal of the towed body received by the m-th hydrophone in the towed array, and L be the distance from the noise source of the towed body to the reference hydrophone, i.e., L = D1, D2. m Let m be the distance from the towed noise source to the m-th hydrophone.

[0018] Furthermore, the array manifold vector A is:

[0019]

[0020] Where e is the base of the natural logarithm, j is the imaginary unit, f0 is the center frequency of the towed body noise source signal, τ1 is the time delay from the towed body noise source to the reference hydrophone, τ2 is the time delay from the towed body noise source to the second hydrophone, and τ M Let M be the time delay from the towed body noise source to the Mth hydrophone, and m be the time delay from the towed body noise source to the mth hydrophone. m = 1, 2, ..., M, where c is the speed of sound.

[0021] Furthermore, the specific process of step one is as follows:

[0022] Step 11: Establish a tow cable motion coordinate system with the tow body as the origin, the direction from the tow body to the reference hydrophone as the positive x-axis, and the normal to the x-axis as the y-axis.

[0023] Step 1 and 2: Represent the signal received by the m-th hydrophone in the towed array at the current moment as x. m (t), let x represent the signal received by the (m+1)th hydrophone in the towed array at the current moment. m+1 (t), according to x m (t) and x m+1 (t) Calculate the time delay κ between the m-th hydrophone and the (m+1)-th hydrophone. m(m+1) ;

[0024] Then the distance D from the (m+1)th hydrophone to the noise source of the tow body m+1 for:

[0025]

[0026] And the distance D from the (m+1)th hydrophone to the noise source of the tow body m+1 Satisfies formula (5);

[0027]

[0028] Where θ is the incident direction of the noise source signal of the towed body, and d is the distance between two adjacent hydrophones in the towed array in the linear array state;

[0029] Step 13: Based on different maneuvering conditions, combine formulas (4) and (5) to calculate the distance D from each hydrophone to the noise source of the towed body. m m = 1, 2, ..., M;

[0030] Step 1, Section 4: Calculate the angle between the line connecting each hydrophone and the origin and the x-axis of the established coordinate system.

[0031]

[0032] Where, η m Let the angle between the line connecting the m-th hydrophone and the origin and the x-axis of the coordinate system.

[0033] Step 15: Calculate the deflection angle of each hydrophone based on the results of Step 14;

[0034] δ m =η m+1 -η m (7)

[0035] Where, δ m Let η be the deflection angle of the m-th hydrophone. m+1 Let the angle between the line connecting the (m+1)th hydrophone and the origin of the coordinate system and the x-axis of the coordinate system.

[0036] Step 16, according to D m and δ m Calculate the position coordinates of the m-th hydrophone;

[0037]

[0038] Where, x m Let x be the x-axis coordinate of the m-th hydrophone, and y be the y-axis coordinate of the m-th m Let y be the y-coordinate of the m-th hydrophone.

[0039] Furthermore, the specific process of steps one and three is as follows:

[0040] Under straight-line maneuvering, all hydrophones in the towed array are in a straight-line state. Then, after establishing equations (4) and (5) for each hydrophone, the equations are solved simultaneously to obtain the distance from each hydrophone to the noise source of the towed body.

[0041] During turning maneuvers, the hydrophones in the towed array are divided into three parts according to their motion state: straight-line state, moderate state, and turning state. For the straight-line state, equations (4) and (5) are established for each hydrophone in the straight-line state, and then the established equations are solved simultaneously to obtain the distance from each hydrophone in the straight-line state to the noise source of the towed body. Similarly, the distance from each hydrophone in the moderate state and the turning state to the noise source of the towed body is calculated.

[0042] Furthermore, the deflection angle of each hydrophone in the rotating state is the same;

[0043] For a hydrophone in a relaxed state, the difference in deflection angle between adjacent hydrophones is γ.

[0044] Furthermore, the step of focusing beamforming based on the towed array configuration to obtain the target azimuth is as follows:

[0045] After randomly dividing the towed array, the target is measured and searched using each subarray. The phase of the hydrophones at different positions is compensated according to the spherical wave to obtain the spatial spectrum of the hydrophones at different positions.

[0046] The spatial spectrum of the hydrophones at different positions is focused and beamformed to output a two-dimensional spatial spectrum P(r,θ). The target azimuth θ in the tow cable motion coordinate system is obtained from the two-dimensional spatial spectrum P(r,θ). t ;

[0047] The two-dimensional spatial spectrum P(r,θ) is:

[0048]

[0049] Among them, a m (r,θ) is the spatial focusing beamforming weight vector of the m-th hydrophone, where the superscript H represents the conjugate transpose, and R... m It is the frequency domain snapshot autocorrelation matrix.

[0050] Furthermore, the step of estimating the target's position and velocity at the current moment based on the target's azimuth and Doppler information specifically involves:

[0051] Step 3.1 The relationship between the first-order Doppler coefficient difference and the near-field target motion state is as follows:

[0052]

[0053] Where, χ nm v is the difference in the first-order Doppler coefficients between the m-th hydrophone and the n-th hydrophone. x (t) represents the component of the target's velocity projected onto the x-axis at the current moment, v y (t) represents the velocity component of the target projected onto the y-axis at the current moment. This represents the angle between the line connecting the target and the m-th hydrophone at the current moment and the x-axis. This represents the angle between the line connecting the target and the nth hydrophone at the current moment and the x-axis;

[0054] Step 3.2: The angle between the line connecting the target and the nth hydrophone and the x-axis. for:

[0055]

[0056] Where x(t) represents the target's coordinate in the x-axis direction at the current moment, and y(t) represents the target's coordinate in the y-axis direction at the current moment. n (t) represents the coordinate of the nth hydrophone in the x-axis direction at the current time, y n (t) represents the coordinate of the nth hydrophone in the y-axis direction at the current time, and satisfies θt (t) represents the target's orientation in the current coordinate system of the tow cable motion, and η n (t) is the angle between the line connecting the nth hydrophone and the origin at the current time and the x-axis of the coordinate system.

[0057] Step 3: The velocity v of the target relative to the nth hydrophone. n (t) is:

[0058]

[0059] Steps 3 and 4: Calculate the first-order Doppler coefficient difference between each pair of hydrophones using frequency domain cross-correlation. Establish equations (10), (11), and (12) for each pair of hydrophones, and then simultaneously solve all equations (10), (11), and (12) to calculate the target's v at the current moment. x (t), v y (t), x(t), and y(t).

[0060] Furthermore, the method further includes a fourth step, which is:

[0061] The target's trajectory is predicted based on its current position and velocity, as well as its velocity in the previous moment. Then, the risk of collision is determined based on the predicted target trajectory and the current towed formation.

[0062] If there is a risk of collision, a turning maneuver is applied to control the vehicle to turn.

[0063] If there is no risk of collision and no new control commands are input, the vehicle will continue to navigate in its current state.

[0064] If there is no risk of collision and new control commands are input, the vehicle will navigate according to the newly input control commands.

[0065] The specific process for determining whether there is a risk of collision is as follows:

[0066] Let v represent the velocity of the target in the x-axis direction at the previous moment. x (t-1), where the velocity of the target in the y-axis direction at the previous moment is expressed as v. y (t-1);

[0067]

[0068] Where Δt is the time difference between the current time and the previous time, and a subx Let a be the acceleration of the target in the x-axis direction. suby Let x be the acceleration of the target in the y-axis direction;

[0069] The target's trajectory is predicted based on acceleration, current position, and velocity. The target's trajectory and current formation are then used to determine if there is a risk of collision.

[0070] The beneficial effects of this invention are:

[0071] This invention solves for the real-time noise data of the towed array received by the towed vehicle, and combines it with a transition curve array fitting model to obtain a more accurate real-time maneuvering array shape than traditional array estimation, without requiring additional information. Using the accurate real-time array shape can improve the accuracy of near-field target localization. Furthermore, by combining the target's position, velocity, and acceleration, the possibility of a collision can be predicted. If a collision is suspected, timely maneuvering to avoid it is necessary. Simultaneously, this invention utilizes the towed vehicle noise for self-correction of the array shape, eliminating the need for additional cooperative sound sources, and has practical application value. Attached Figure Description

[0072] Figure 1 This is a flowchart of a near-field target localization method at sea based on formation estimation according to the present invention;

[0073] Figure 2 This is a schematic diagram of the towed array's maneuvering state in this invention;

[0074] Figure 3 This is a schematic diagram of the broadband focusing beamforming process based on subarray in this invention;

[0075] In the figure, x, y, and z are the three coordinate axes of the three-dimensional rectangular coordinate system, O is the origin of the three-dimensional rectangular coordinate system, (x, y, z0) are the coordinates of the scan grid point, (x0, y0, z0) are the near-field target positions, and the solid dots represent the hydrophones of the towed array.

[0076] Figure 4 This is a schematic diagram illustrating the real-time estimation of the motion state of the towed body noise source in this invention.

[0077] In the figure, (x n ,y n () represents the position of the nth hydrophone. Let (x(t), y(t)) represent the angle between the line connecting the target and the nth hydrophone and the x-axis, (x(t), y(t)) represent the position of the near-field target at the current moment, and v represent the target's velocity. x v represents the component of the target's velocity projected onto the x-axis. y v represents the component of the target's velocity projected onto the y-axis. n Let be the velocity of the target relative to the nth hydrophone. Detailed Implementation

[0078] Specific Implementation Method 1: Combination Figure 1This embodiment describes a near-field target localization method at sea based on formation estimation. The method specifically includes the following steps:

[0079] Step 1: Calculate the position of each hydrophone in the towed array at the current moment based on the signals received by each hydrophone in the towed array at the current moment;

[0080] Step 2: Based on the mechanical model of the towed array and tow cable at the current moment and the position of each hydrophone, obtain the formation of the towed array at the current moment.

[0081] If the vehicle is in a straight-line maneuver, the current formation of the towed array is obtained based on the mechanical model of the towed array and tow cable in the straight-line maneuver, as well as the positions of each hydrophone. If the vehicle is in a turning maneuver, the mechanical model of the towed array and tow cable is divided into three parts: a circular arc mechanical model, a transition curve mechanical model, and a straight-line motion mechanical model. For the circular arc segment, the formation of the circular arc segment is obtained based on the circular arc mechanical model and the positions of the hydrophones in the circular arc motion. Similarly, the formations of the transition curve segment and the straight-line segment are obtained separately. The formations of the circular arc segment, the transition curve segment, and the straight-line segment together constitute the formation of the towed array.

[0082] Step 3: Focus beamforming is performed based on the towed array configuration to obtain the target's azimuth; then, the target's position and velocity at the current moment are estimated based on the target's azimuth and Doppler information.

[0083] The method of this invention can locate the target in real time and determine whether there is a risk of collision between the maritime vehicle and the target based on the positioning results at two different times. If there is a risk of collision, the vehicle can maneuver away in time to avoid collision with the target and thus avoid danger to the vehicle.

[0084] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the towed array is an array composed of M isotropic hydrophones.

[0085] In the linear array state, the towed array is a uniform linear array. According to the distance between each hydrophone and the noise source of the tow body in the linear array state, each hydrophone is sequentially numbered as the 1st hydrophone, the 2nd hydrophone, ..., the Mth hydrophone. That is, the hydrophone with the smallest distance from the noise source of the tow body is numbered as the 1st hydrophone, and the hydrophone with the largest distance from the noise source of the tow body is numbered as the Mth hydrophone. The 1st hydrophone is used as the reference hydrophone.

[0086] The other steps and parameters are the same as in Specific Implementation Method 1.

[0087] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that the towed body noise source is located in the near-field range of the towed array, and the signal received by the towed array is:

[0088] x(t)=A·S(t)+N(t) (1)

[0089] Where x(t) is the signal vector received by the towed array at the current moment, and the dimension of x(t) is M×1, x(t)=[x1(t),x2(t),…,x M [(t)],x1(t),x2(t),…,x M (t) is the signal received by the 1st, 2nd, ..., Mth hydrophone in the towed array at the current moment, S(t) is the tow body noise source signal vector received by the towed array at the current moment, and the dimension of S(t) is M×1. N(t) is the environmental additive noise signal vector received by the towed array at the current moment, and the dimension of N(t) is M×1. A is the M-dimensional array manifold vector.

[0090] The signal strength received by each hydrophone in the towed array is:

[0091]

[0092] Where, p m (t) represents the signal strength received by the m-th hydrophone in the towed array, where n m (t) represents the additive environmental noise signal received by the m-th hydrophone in the towed array, μ m Let s(t-μ) be the time difference between the towed body noise source signal and the m-th hydrophone. m Let be the noise source signal of the towed body received by the m-th hydrophone in the towed array, and L be the distance from the noise source of the towed body to the reference hydrophone, i.e., L = D1, D2. m Let m be the distance from the towed noise source to the m-th hydrophone.

[0093] Other steps and parameters are the same as in specific implementation method one or two.

[0094] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the array manifold vector A is:

[0095]

[0096] Where e is the base of the natural logarithm, j is the imaginary unit, f0 is the center frequency of the towed body noise source signal, τ1 is the time delay from the towed body noise source to the reference hydrophone, τ2 is the time delay from the towed body noise source to the second hydrophone, and τ M Let M be the time delay from the towed body noise source to the Mth hydrophone, and m be the time delay from the towed body noise source to the mth hydrophone. m = 1, 2, ..., M, where c is the speed of sound.

[0097] The other steps and parameters are the same as those in one of the specific implementation methods one to three.

[0098] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the specific process of step one is as follows:

[0099] Step 11: Establish a tow cable motion coordinate system with the tow body as the origin, the direction from the tow body to the reference hydrophone as the positive x-axis, and the normal to the x-axis as the y-axis.

[0100] Step 1 and 2: Represent the signal received by the m-th hydrophone in the towed array at the current moment as x. m (t), let x represent the signal received by the (m+1)th hydrophone in the towed array at the current moment. m+1 (t), according to x m (t) and x m+1 (t) Calculate the time delay κ between the m-th hydrophone and the (m+1)-th hydrophone. m(m+1) ;

[0101] Then the distance D from the (m+1)th hydrophone to the noise source of the tow body m+1 for:

[0102]

[0103] And the distance D from the (m+1)th hydrophone to the noise source of the tow body m+1 Formula (5) is satisfied when the interval between adjacent hydrophones is close (i.e. the cable between adjacent hydrophones is approximately a straight line).

[0104]

[0105] Where θ is the incident direction of the noise source signal of the towed body, and d is the distance between two adjacent hydrophones in the towed array in the linear array state;

[0106] Step 13: Based on different maneuvering conditions, combine formulas (4) and (5) to calculate the distance D from each hydrophone to the noise source of the towed body. m m = 1, 2, ..., M;

[0107] Step 1, Section 4: Calculate the angle between the line connecting each hydrophone and the origin and the x-axis of the established coordinate system.

[0108]

[0109] Where, η m Let the angle between the line connecting the m-th hydrophone and the origin and the x-axis of the coordinate system.

[0110] Step 15: Calculate the deflection angle of each hydrophone based on the results of Step 14;

[0111] δ m =ηm+1 -η m (7)

[0112] Where, δ m Let η be the deflection angle of the m-th hydrophone. m+1 Let the angle between the line connecting the (m+1)th hydrophone and the origin of the coordinate system and the x-axis of the coordinate system.

[0113] Step 16, according to D m and δ m Calculate the position coordinates of the m-th hydrophone;

[0114]

[0115] Where, x m Let x be the x-axis coordinate of the m-th hydrophone, and y be the y-axis coordinate of the m-th m Let y be the y-coordinate of the m-th hydrophone.

[0116] The other steps and parameters are the same as those in one of the specific implementation methods one to four.

[0117] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the specific process of step one to three is as follows:

[0118] Under straight-line maneuvering, all hydrophones in the towed array are in a straight-line state. Then, after establishing equations (4) and (5) for each hydrophone, the equations are solved simultaneously to obtain the distance from each hydrophone to the noise source of the towed body.

[0119] During turning maneuvers, the hydrophones in the towed array are divided into three parts according to their motion state: straight-line state, moderate state, and turning state. For the straight-line state, equations (4) and (5) are established for each hydrophone in the straight-line state, and then the established equations are solved simultaneously to obtain the distance from each hydrophone in the straight-line state to the noise source of the towed body. Similarly, the distance from each hydrophone in the moderate state and the turning state to the noise source of the towed body is calculated.

[0120] The other steps and parameters are the same as those in one of the specific implementation methods one to five.

[0121] During detection missions, maneuvering commands are frequently issued. Upon receiving these commands, the towed platform will adjust its position by either traveling straight or turning. During straight maneuvers, the towed array is approximately straightened, with minimal changes in its array shape and a relatively stable array manifold. During turning maneuvers, the abrupt change in the towed platform's state is gradually transmitted along the tow cable to each receiving hydrophone until the tail of the array. During turning maneuvers, each hydrophone on the towed array experiences three motion states: straight, gradual, and turning. Therefore, for a towed array containing a series of hydrophone elements, after the towed platform begins its maneuver, its motion model is one or a combination of "straight line," "gradual curve," and "circular arc."

[0122] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that each hydrophone in the rotating state has the same deflection angle;

[0123] For a hydrophone in a relaxed state, the difference in deflection angle between adjacent hydrophones is γ.

[0124] For those in the rotation state, i.e., in the... Figure 2 The deflection angle of each hydrophone in the circular arc motion model is a fixed value δ. int , i.e. δ m =η m+1 -η m ,δ2=…δ M-1 =δ int For those in a moderate state, that is, in a state of equilibrium... Figure 2 In the moderate curvilinear motion model, each hydrophone (in the turning maneuver, except for those in straight-line and turning states, the other hydrophones are in a moderate state) has a fixed deflection angle difference of γ between adjacent hydrophones, i.e., δ. m =η m+1 -η m δ m -δ m-1 =γ.

[0125] The other steps and parameters are the same as those in one of the specific implementation methods one to six.

[0126] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One through Seven in that the step of focusing beamforming based on the towed array formation to obtain the target azimuth is as follows:

[0127] After randomly dividing the towed array, the target is measured and searched using each subarray. The phase of the hydrophones at different positions is compensated according to the spherical wave to obtain the spatial spectrum of the hydrophones at different positions.

[0128] The spatial spectrum of the hydrophones at different positions is focused and beamformed to output a two-dimensional spatial spectrum P(r,θ). The target azimuth θ in the tow cable motion coordinate system is obtained from the two-dimensional spatial spectrum P(r,θ).t ;

[0129] The two-dimensional spatial spectrum P(r,θ) is:

[0130]

[0131] Among them, a m (r,θ) is the spatial focusing beamforming weight vector of the m-th hydrophone, where the superscript H represents the conjugate transpose, and R... m It is the frequency domain snapshot autocorrelation matrix.

[0132] The other steps and parameters are the same as those in any of the specific implementation methods one to seven.

[0133] like Figure 3 As shown, when the focused scan finds the true location of the near-field towed body noise source, the signals of each hydrophone are added in phase to maximize the output power, thereby forming a spectral peak at the spatial spectrum overlap and achieving azimuth localization.

[0134] Detailed Implementation Method Nine: Combination Figure 4 This embodiment is described below. The difference between this embodiment and specific embodiments one through eight is that the estimation of the target's current position and velocity based on the target's azimuth and Doppler information is as follows:

[0135] Step 3.1 The relationship between the first-order Doppler coefficient difference and the near-field target motion state is as follows:

[0136]

[0137] Where, χ nm v is the difference in the first-order Doppler coefficients between the m-th hydrophone and the n-th hydrophone. x (t) represents the component of the target's velocity projected onto the x-axis at the current moment, v y (t) represents the velocity component of the target projected onto the y-axis at the current moment. This represents the angle between the line connecting the target and the m-th hydrophone at the current moment and the x-axis. This represents the angle between the line connecting the target and the nth hydrophone at the current moment and the x-axis;

[0138] Step 3.2: The angle between the line connecting the target and the nth hydrophone and the x-axis. for:

[0139]

[0140] Where x(t) represents the target's coordinate in the x-axis direction at the current moment, and y(t) represents the target's coordinate in the y-axis direction at the current moment. n (t) represents the coordinate of the nth hydrophone in the x-axis direction at the current time, y n(t) represents the coordinate of the nth hydrophone in the y-axis direction at the current time, and satisfies θ t (t) represents the target's orientation in the current coordinate system of the tow cable motion, and η n (t) is the angle between the line connecting the nth hydrophone and the origin at the current time and the x-axis of the coordinate system.

[0141] Step 3: The velocity v of the target relative to the nth hydrophone. n (t) is:

[0142]

[0143] Steps 3 and 4: Calculate the first-order Doppler coefficient difference between each pair of hydrophones using frequency domain cross-correlation. Establish equations (10), (11), and (12) for each pair of hydrophones, and then simultaneously solve all equations (10), (11), and (12) to calculate the target's v at the current moment. x (t), v y (t), x(t), and y(t).

[0144] The other steps and parameters are the same as those in one of the specific implementation methods one to eight.

[0145] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that it further includes step four, which is as follows:

[0146] The target's trajectory is predicted based on its current position and velocity, as well as its velocity in the previous moment. Then, the risk of collision is determined based on the predicted target trajectory and the current towed formation.

[0147] If there is a risk of collision, a turning maneuver is applied to control the vehicle to turn.

[0148] If there is no risk of collision and no new control commands are input, the vehicle will continue to navigate in its current state.

[0149] If there is no risk of collision and new control commands are input, the vehicle will navigate according to the newly input control commands.

[0150] The specific process for determining whether there is a risk of collision is as follows:

[0151] Let v represent the velocity of the target in the x-axis direction at the previous moment. x (t-1), where the velocity of the target in the y-axis direction at the previous moment is expressed as v. y (t-1);

[0152]

[0153]

[0154] Where Δt is the time difference between the current time and the previous time, and a subx Let a be the acceleration of the target in the x-axis direction. suby Let x be the acceleration of the target in the y-axis direction;

[0155] The target's trajectory is predicted based on acceleration, current position, and velocity. The target's trajectory and current formation are then used to determine if there is a risk of collision.

[0156] The other steps and parameters are the same as those in any of the specific implementation methods one to nine.

[0157] Based on the position, velocity, and acceleration of the near-field target, it is possible to calculate the timeframe and direction in which the target will approach or move away from the towed array system. When the target approaches along the direction of the towed array system, it is necessary to maneuver away in a timely manner to avoid a collision.

[0158] The above examples of the present invention are merely illustrative of the computational model and process of the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is impossible to exhaustively list all possible implementations here. Any obvious variations or modifications derived from the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for locating near-field targets at sea based on formation estimation, characterized in that, The method specifically includes the following steps: Step 1: Calculate the position of each hydrophone in the towed array at the current moment based on the signals received by each hydrophone in the towed array at the current moment; The specific process of step one is as follows: Step 11: Establish a coordinate system with the towed body as the origin and the direction from the towed body to the reference hydrophone as the coordinate axis. positive axis direction, with The normal direction of the axis is The coordinate system for the cable-driven motion of the axis; Step 1 and 2: Drag the current position in the array... The signal received by each hydrophone is represented as follows: Drag the current moment into the formation The signal received by each hydrophone is represented as follows: ,according to and Calculate the first The hydrophone and the first Time delay between hydrophones ; Then the first Distance from the hydrophone to the noise source of the tow body for: (4) in, The distance from the towed body noise source to the reference hydrophone is denoted as . Speed ​​of sound; And the first Distance from the hydrophone to the noise source of the tow body Satisfies formula (5); (5) in, The incident direction of the noise source signal is the drag body. In a linear array configuration, the distance between two adjacent hydrophones in a towed array; Step 13: Based on different maneuvering conditions, combine formulas (4) and (5) to calculate the distance from each hydrophone to the noise source of the towed body. , , This represents the total number of hydrophones. The specific process of steps one and three is as follows: Under straight-line maneuvering, all hydrophones in the towed array are in a straight-line state. Then, after establishing equations (4) and (5) for each hydrophone, the equations are solved simultaneously to obtain the distance from each hydrophone to the noise source of the towed body. During turning maneuvers, the hydrophones in the towed array are divided into three parts according to their motion state: straight-line state, moderate state, and turning state. For the straight-line state, equations (4) and (5) are established for each hydrophone in the straight-line state, and then the established equations are solved simultaneously to obtain the distance from each hydrophone in the straight-line state to the noise source of the towed body. Similarly, the distance from each hydrophone in the moderate state and the turning state to the noise source of the towed body is calculated. Step 1, Section 4: Calculate the line connecting each hydrophone and the origin to the established coordinate system. The included angle of the axis; (6) in, For the first The line connecting the hydrophone and the origin of the coordinate system is used to establish the coordinate system. The included angle of the axis, For drag body noise source to the first The distance between the hydrophones; Step 15: Calculate the deflection angle of each hydrophone based on the results of Step 14; (7) in, For the first The angle of the hydrophone For the first The line connecting the hydrophone and the origin of the coordinate system is used to establish the coordinate system. The included angle of the axis; Step 16, according to and Calculate the first The location coordinates of the hydrophone; (8) in, For the first A hydrophone Axis coordinates For the first A hydrophone Axis coordinates; Step 2: Based on the mechanical model of the towed array and tow cable at the current moment and the position of each hydrophone, obtain the formation of the towed array at the current moment. Step 3: Focus beamforming is performed based on the towed array configuration to obtain the target's azimuth; then, the target's position and velocity at the current moment are estimated based on the target's azimuth and Doppler information.

2. The method for locating near-field targets at sea based on formation estimation according to claim 1, characterized in that, The drag array is composed of An array of isotropic hydrophones; In the linear array configuration, the towed array is a uniform linear array. Based on the distance between each hydrophone and the noise source of the towed body in the linear array configuration, the hydrophones are sequentially numbered as the 1st hydrophone, the 2nd hydrophone, ..., the 3rd hydrophone. The hydrophones are numbered as follows: the hydrophone closest to the noise source of the tow body is numbered as the first hydrophone, and the hydrophone furthest from the noise source of the tow body is numbered as the second hydrophone. There are 10 hydrophones, and the first hydrophone is used as the reference hydrophone.

3. The method for locating near-field targets at sea based on formation estimation according to claim 2, characterized in that, The signal received by the towed array is: (1) in, This represents the current signal vector received by the towed array. The dimension is , , It is the 1st, 2nd, ..., 1st in the drag array at the current moment. The signal received by the hydrophone This represents the noise source signal vector of the towed array received at the current moment. The dimension is , The vector of the additive environmental noise signal received by the towed array at the current moment. The dimension is , for A dimensional array of manifold vectors; The signal strength received by each hydrophone in the towed array is: (2) in, For the dragging formation The strength of the signal received by each hydrophone For the dragging formation An ambient additive noise signal received by a hydrophone For the tow body noise source signal from the reference hydrophone to the first The time difference between the hydrophones For the dragging formation The signal from the tow body noise source received by the hydrophone. The distance from the towed noise source to the reference hydrophone is... , For the drag body noise source to the first The distance of a hydrophone.

4. The method for locating near-field targets at sea based on formation estimation according to claim 3, characterized in that, The array manifold vector for: (3) in, is the base of the natural logarithm. The imaginary unit, The center frequency of the noise source signal is the drag body. The time delay from the towed body noise source to the reference hydrophone. The time delay from the tow body noise source to the second hydrophone. For the drag body noise source to the first The time delay of the hydrophone, the drag noise source to the first The delay of a hydrophone , , The speed of sound.

5. A method for locating near-field targets at sea based on formation estimation according to claim 4, characterized in that, Each hydrophone in the rotating state has the same deflection angle; For a hydrophone in a relaxed state, the difference in deflection angle between adjacent hydrophones is... .

6. The method for locating near-field targets at sea based on formation estimation according to claim 5, characterized in that, The target azimuth is obtained by focusing the beam according to the towed array configuration; Specifically: After randomly dividing the towed array, the target is measured and searched using each subarray. The phase of the hydrophones at different positions is compensated according to the spherical wave to obtain the spatial spectrum of the hydrophones at different positions. Focusing beamforming is performed on the spatial spectrum of hydrophones at different locations to output a two-dimensional spatial spectrum. According to the two-dimensional spatial spectrum Obtain the target orientation in the tow cable motion coordinate system ; The two-dimensional spatial spectrum for: (9) in, For the first The spatial focusing beamforming weight vector of the hydrophone is given by the superscript H, which represents the conjugate transpose. It is the frequency domain snapshot autocorrelation matrix.

7. A method for locating near-field targets at sea based on formation estimation according to claim 6, characterized in that, The step of estimating the target's position and velocity at the current moment based on the target's azimuth and Doppler information is as follows: Step 3.1 The relationship between the first-order Doppler coefficient difference and the near-field target motion state is as follows: (10) in, For the first The hydrophone and the first The difference in the first-order Doppler coefficients of the hydrophones This represents the velocity component projected onto the x-axis at the current moment. This represents the velocity component projected onto the y-axis at the current moment. Indicates the target at the current moment and the first... The angle between the line connecting the hydrophones and the x-axis. Indicates the target at the current moment and the first... The angle between the line connecting the hydrophones and the x-axis; Step 3.2, Objectives and... The angle between the line connecting the hydrophones and the x-axis for: (11) in, This represents the target's coordinates along the x-axis at the current moment. This represents the target's coordinates along the y-axis at the current moment. Indicates the current time. The coordinates of the hydrophone along the x-axis. Indicates the current time. The coordinates of a hydrophone in the y-axis direction, and satisfying , It is the target's orientation in the current coordinate system of the tow cable's motion. For the current moment The line connecting the hydrophone and the origin of the coordinate system is used to establish the coordinate system. The included angle of the axis; Step 3.3, the target relative to the first The speed of the hydrophone for: (12) Steps 3 and 4: The first-order Doppler coefficient difference between each pair of hydrophones is calculated through frequency domain cross-correlation. Equations (10), (11), and (12) are then established for each pair of hydrophones. Finally, all equations (10), (11), and (12) are solved simultaneously to calculate the target's current position. , , and .

8. A method for locating near-field targets at sea based on formation estimation according to claim 7, characterized in that, The method further includes a fourth step, which is: The target's trajectory is predicted based on its current position and velocity, as well as its velocity in the previous moment. Then, the risk of collision is determined based on the predicted target trajectory and the current towed formation. If there is a risk of collision, a turning maneuver is applied to control the vehicle to turn. If there is no risk of collision and no new control commands are input, the vehicle will continue to navigate in its current state. If there is no risk of collision and new control commands are input, the vehicle will navigate according to the newly input control commands. The specific process for determining whether there is a risk of collision is as follows: Let the velocity of the target in the x-axis direction at the previous moment be expressed as... The velocity of the target in the y-axis direction at the previous moment is expressed as... ; (13) (14) in, The time difference between the current moment and the previous moment. Let x be the acceleration of the target in the x-axis direction. Let x be the acceleration of the target in the y-axis direction; The target's trajectory is predicted based on acceleration, current position, and velocity. The target's trajectory and current formation are then used to determine if there is a risk of collision.

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