A method for calibrating the position of a mobile array using multi-beam signals

Abstract

The present invention discloses a method for calibrating the position of a mobile array using multi-beam signals, which relates to the field of sonar motion and compensation technology. The technical key points include the following steps: S1, obtaining the sound velocity profile, reverberation and background noise of the target water body, and constructing a three-dimensional coordinate accurate positioning system for the motion of linear array transducer primitives; S2, coarsely positioning the carrier, and deploying transponders at the same time to position each array element; S3, collecting imaging data, and using calibration hydrophones to simultaneously record transponder cooperation signals, performing multi-beam matched filtering to take maximum values ​​to establish a three-dimensional positioning model for the position of the mobile array; S4, obtaining the three-dimensional position coordinate information of the array element, and by correcting the error of the imaging algorithm, performing downward high-resolution imaging of the acoustic target. The present invention realizes the accurate positioning of the three-dimensional coordinates of the transducer primitives in the virtual synthetic array through the design and constraints of the hardware structure, thereby completing the imaging of underwater targets with high resolution.

Description

Technical Field

[0001] The invention relates to the technical field of sonar motion and compensation, and in particular to a method for calibrating a mobile array position by using a multi-beam signal. Background Art

[0002] Downward-looking linear array is one of the common forms of multi-beam sonar systems. It has the advantages of simple structural design and large actual aperture, which can fully improve the target imaging resolution in the array direction. In order to fully reproduce the clear structural acoustic image of underwater targets, the application of linear array needs to overcome its disadvantage of insufficient resolution in the normal direction.

[0003] The main sources of motion errors are the irregular shaking of the surface platform caused by wind, waves and currents, the uneven change of sound speed in water, and the instability of the water medium for sound propagation, etc., which will be directly reflected in the position deviation of each element of the virtual synthetic array, and have a direct impact on the final underwater target imaging resolution. Therefore, motion error estimation and real-time position calibration of the mobile array become the key to high-quality imaging.

[0004] In the test scenario of linear array motion synthesis virtual array, due to the requirement of coherent superposition, the one-way sound path error must be less than one-eighth of the sound wavelength to ensure the consistency of the positions of each element of the virtual array. Simply relying on the hardware positioning system (including GPS, inertial navigation, etc.) to provide the real-time position accuracy of the mobile array cannot meet the above requirements. The joint motion compensation method based on sonar echo data and underwater navigation equipment can improve positioning accuracy, but navigation hardware is generally expensive. At the same time, the phase center overlap method (Displaced Phase Center, DPC) used based on sonar echo data relies on the continuous echo data of motion, which will accumulate errors and cause the algorithm to fail after reaching a certain level. Therefore, a mobile array position calibration technology that does not rely on underwater navigation positioning systems and traditional DPC algorithms is needed to ensure high-quality imaging of underwater targets. Summary of the invention

[0005] The purpose of the present invention is to solve the above problems and provide a method for calibrating the position of a mobile array using multi-beam signals.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows: A method for calibrating the position of a mobile array using a multi-beam signal comprises the following steps:

[0007] S1. In the target waters, a cross-shaped calibration hydrophone array structure is set up manually to form a three-dimensional coordinate precise positioning system for the linear array transducer element motion;

[0008] S2. Use Beidou and GPS satellite positioning systems to roughly locate the carrier, deploy transponders in the target area, and use the linear array transducer primitive motion three-dimensional coordinate precise positioning system to locate each array element at the millimeter level;

[0009] S3, performing imaging data acquisition, and in the process of imaging data acquisition, using a calibrated hydrophone to simultaneously record the transponder cooperation signal, performing multi-beam matched filtering to obtain the maximum value and establishing a three-dimensional positioning model of the mobile array position;

[0010] S4. Obtain the three-dimensional position coordinate information of the array element, and perform downward-looking high-resolution imaging of the acoustic target by correcting the error of the imaging algorithm.

[0011] Preferably, in step S1, the hydrophone array structure is used to obtain information such as sound velocity profile distribution, water flow velocity, reverberation, background noise, etc. of the target water area.

[0012] Preferably, in step S4, the modified imaging algorithm includes using background noise and reverberation to perform data preprocessing and using sound velocity profile to perform error correction.

[0013] The present invention also provides a sonar posture measurement system using the above method, characterized in that: the system includes an electronic warehouse, a towed body, a linear array transducer element and a target, the electronic warehouse is arranged above the towed body, the linear array transducer element is connected to the bottom of the towed body, the target is arranged on the bottom of the water, the linear array transducer element is composed of a calibration hydrophone, an active sound source is arranged in the middle of the linear array transducer element, and a wireless calibration sound source is arranged in the middle of the target.

[0014] Compared with the prior art, this solution has the following beneficial effects:

[0015] The method of the present invention can take advantage of the high efficiency of multi-beam receiving and accurately calibrate the real-time position of the mobile array. The calibration error is only at the sub-wavelength level, thereby ensuring the accurate acquisition of the three-dimensional coordinates of each primitive in the synthetic virtual array and significantly improving the imaging quality of underwater targets. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a flowchart of the multi-beam signal calibration mobile array position in an embodiment of the present invention;

[0017] Figure 2 This is the first acquisition of the three-dimensional position information of the array element in the embodiment of the present invention;

[0018] Figure 3 is an assembly diagram of a sonar attitude measurement system in an embodiment of the present invention;

[0019] Figure 4 It is a working schematic diagram of the sonar attitude measurement system in an embodiment of the present invention.

[0020] Among them: 1. Electronic warehouse; 101. Central control platform; 2. Towed body; 3. Linear array transducer element; 301. Active sound source; 302. Hydrophone; 4. Target; 401. Wireless calibration sound source; 5. Cable; 6. Direct sound line of calibration sound source; 7. Combined inertial navigation; 8. Object plane; 9. Imaging plane; 10. Water surface. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the solution of the present invention, the technical solution of the present invention will be further described in detail below in conjunction with the embodiments of the present invention and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0022] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0023] Example:

[0024] The present invention aims to solve the problem of insufficient imaging resolution of the downward-looking horizontal linear array in the normal direction. The linear array is mounted on a surface platform and moves linearly along the normal direction to synthesize a virtual array to perform high-resolution imaging of underwater targets. The imaging performance of the virtual array is affected by the position error of the moving array and is reduced. In principle, the traditional shift phase center (DPC) method can perform self-focusing motion compensation based on echo data, but the delay estimation of the correlation peak may result in huge estimation errors, causing the DPC self-focusing algorithm to fail.

[0025] The present invention proposes a method for calibrating the position of a mobile array using multi-beam cooperative signals. Through the design and constraints of the hardware structure, the three-dimensional coordinates of the transducer elements in the virtual synthetic array are accurately positioned, thereby completing underwater target imaging with higher resolution.

[0026] A method for calibrating the position of a mobile array using a multi-beam signal, wherein the method of calibrating the mobile array using a multi-beam signal specifically uses a transponder cooperative signal received by multiple channels of the multi-beam to perform ranging, and specifically includes the following steps:

[0027] First, after reaching the target waters, a cross-shaped calibration hydrophone array structure is set up manually to obtain information such as the sound velocity profile distribution, water flow velocity, reverberation, and background noise of the target waters.

[0028] Step 2: Use Beidou and GPS satellite positioning systems to roughly locate the carrier, deploy transponders in the target area, and use the linear array transducer primitive motion three-dimensional coordinate precise positioning system to locate each array element at the millimeter level;

[0029] The third step is to use the calibration hydrophone to simultaneously record the transponder cooperation signal during the imaging data acquisition process, perform multi-beam matched filtering to obtain the maximum value and establish a three-dimensional positioning model for the mobile array position;

[0030] Step 4: The imaging array enters the water and uses the equipment carried by the towed body to travel in a straight line at a constant speed. The three-dimensional high-precision position coordinate information of the array elements is obtained, the error of the imaging algorithm is corrected, and downward imaging of the acoustic target is performed.

[0031] The background noise and reverberation are used for data preprocessing, the sound velocity profile is used for error correction, and high-resolution imaging of the target is achieved by applying the positioning solution information in combination with the time domain backprojection method.

[0032] In this embodiment, the hydrophone element of the downward line-of-sight array sonar imaging system receives the calibration signal emitted by the underwater preset calibration sound source while receiving the target scattered echo signal. By reasonably setting the acoustic emission period and delay of the calibration sound source to adapt it to the emission period of the active sound source and the target depth, so that the calibration sound source signal and the target echo signal fall within the same sound signal acquisition window, the signal of the calibration sound source can be used to locate each hydrophone element. It should be noted that the calibration sound source has a certain range of action. When the calibration sound source is far away from the sonar array, the calibration sound source signal received by the hydrophone element will be buried in the background noise and cannot be effectively extracted.

[0033] In this embodiment, in order to realize acoustic calibration, a sonar attitude measurement algorithm is performed based on multi-point positioning for the received calibration sound source signal. The algorithm makes full use of the calibration signal received by each hydrophone element, positions the sonar system based on the idea of ​​least squares, and has good adaptability to the system.

[0034] In the sonar attitude measurement algorithm based on multi-point positioning, the ship-borne transmitting transducer transmits a pulse interrogation signal to the underwater transponder. After receiving the interrogation signal, the transponder transmits a response pulse signal different from the interrogation signal. The response pulse signal is received by several hydrophone primitives with a spacing of several centimeters. The distance and azimuth of the transponder are calculated based on the round-trip time and phase difference of the sound wave propagating in the water, thereby calculating the coordinates of the transponder. When the absolute coordinates of the transponder are known, the precise coordinates of the carrier can be obtained through coordinate transformation.

[0035] In this embodiment, in the sonar posture measurement based on multi-point positioning, a fixed calibration sound source is laid underwater through a cable wired connection, and a pulse signal can be periodically emitted. The 64 hydrophone primitives of the downward line-of-sight array sonar are used to simultaneously receive the target echo signal and the calibration sound source signal. Since the time when the calibration sound source transmits the signal is slightly later than the time when the carrier sound source transmits the signal, the calibration sound source signal and the signal used for imaging can be separated during the data processing process. At the same time, the calibration sound source signal received by the 64 hydrophone primitives is used for echo ranging, and the relative position coordinates of the underwater calibration sound source are calculated by the least squares method. Similar to the three-point positioning method, since the absolute coordinates of the calibration sound source have been determined when it is laid, the absolute coordinates of each hydrophone primitive and the carrier sound source can be obtained by coordinate transformation.

[0036] The sonar pose measurement algorithm based on multi-point positioning is as follows:

[0037] (1) Calculate the distance from each hydrophone element to the calibration sound source

[0038] In a downward line-of-sight array sonar system that includes a calibration sound source, the echo signal received by the hydrophone element consists of two parts: one is the imaging signal containing target information, and the other is the calibration signal containing the location information of the calibration sound source. The echo signal received by the sonar can be written as follows:

[0039] s r (n) = s cx (n)+s bj (n) (1)

[0040] Among them, s r (n) is the echo signal after sampling, s cx (n) and s bj (n) represent the imaging signal and calibration signal after sampling. Pulse compression is performed on the calibration signal, and the sampling point N corresponding to the maximum amplitude of the calibration signal is taken. max , should meet the following requirements:

[0041] s bj (N max )=max{|s bj (n)|} (2)

[0042] The distance from the hydrophone element receiving the calibration signal to the calibration sound source can be calculated by the following formula:

[0043]

[0044] Among them, N start The number of delay points of channel transmission, N delay The delay points of the calibrated sound source.

[0045] (2) Calculate the relative coordinates of the calibration sound source using the Newton iteration method

[0046] In the process of downward line-of-sight sonar motion imaging, it is necessary to calculate the relative position coordinates of the calibration sound source in each frame. In a certain frame, the relative coordinates of the calibration sound source are X bj =(x bj ,y bj ,z bj ), let the distance from the Array No. hydrophone to the calibration sound source be R Array The relative coordinates of the calibration sound source can be obtained by a nonlinear equation system consisting of 64 equations F(X) = 0. Based on the idea of ​​least squares method, the Newton iteration method is used to calculate the relative coordinates of the calibration sound source. The algorithm flow is as follows:

[0047] Step 1: Set initial parameters

[0048] Assume that the initial relative coordinates of the calibration sound source are (x0, y0, z0), and the maximum number of iterations is N. break , assuming the maximum allowable error is δ tol In order to reduce the number of iterations, the initial relative coordinates of the calibration sound source should be set as close to the actual value as possible.

[0049] Step 2: Calculate the Jacobian matrix of the equation system

[0050] The Arrayth equation can be expressed as follows:

[0051]

[0052] The nonlinear equations can be written in the following simplified form:

[0053]

[0054] Then the Jacobian matrix of the nonlinear equation system can be written as:

[0055]

[0056] Step 3: Iteratively solve the relative coordinates of the calibration sound source

[0057] The iterative format of Newton's iteration method is:

[0058] X (k+1) =X (k) -F'(X (k) ) -1 F(X (k) ) (7)

[0059] The termination condition of the iteration is ||X (k+1) -X (k) || ∞ <δtol , or the iteration reaches the maximum number of iterations N break After the iteration, the relative coordinate X of the calibration sound source of the i-th frame can be obtained. i,bj =(x i,bj ,y i,bj ,z i,bj ).

[0060] (3) Using coordinate transformation to solve the absolute coordinates of each hydrophone element and carrier sound source

[0061] The coordinates in the relative coordinate system can be converted into the coordinates in the absolute coordinate system through linear transformation. After the system is deployed, the absolute position coordinates of the calibration sound source are determined. Let the absolute position coordinates of the calibration sound source be P abs,bj (x abs,bj ,y abs,bj ,z abs,bj ). Generally, the sound source position can also be calibrated as the center of the imaging space. In this case, the absolute position coordinates of the calibrated sound source are (0,0,0).

[0062] In order to obtain the relative coordinates X of the calibration sound source in the i-th frame i,bj Afterwards, the absolute coordinates P of each hydrophone primitive in the i-th frame are i,Array (x i,Array ,y i,Array , z i,Array ) and the absolute coordinates P of the carrier sound source i,source (x i,source ,y i,source , z i,source ) can be calculated by the following formula:

[0063]

[0064] The above specific embodiments are merely explanations of the present invention and are not limitations of the present invention. After reading this specification, those skilled in the art may make modifications to the embodiments without any creative contribution as needed. However, such modifications are protected by the patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for calibrating the position of a mobile array using multi-beam signals, characterized in that: The following steps are involved: S1. In the target waters, a cross-shaped calibration hydrophone array structure is set up manually to form a three-dimensional coordinate precise positioning system for the linear array transducer element motion; S2. Use Beidou and GPS satellite positioning systems to roughly locate the carrier, deploy transponders in the target area, and use the linear array transducer primitive motion three-dimensional coordinate precise positioning system to perform multi-point positioning on each array element; S3, performing imaging data acquisition, and in the process of imaging data acquisition, using a calibrated hydrophone to simultaneously record the transponder cooperation signal, performing multi-beam matched filtering to obtain the maximum value and establishing a three-dimensional positioning model of the mobile array position; S4. Obtain the three-dimensional position coordinate information of the array element, and perform downward-looking high-resolution imaging of the acoustic target by correcting the error of the imaging algorithm.

2. A method for calibrating the position of a mobile array using multi-beam signals according to claim 1, characterized in that: In step S1, the hydrophone array structure is used to obtain the sound velocity profile distribution, water flow velocity, reverberation, and background noise information of the target water area.

3. The method for calibrating the position of a mobile array using multi-beam signals according to claim 1, characterized in that: In step S4, the modified imaging algorithm includes using background noise and reverberation to perform data preprocessing and using sound velocity profile to perform error correction.

4. A sonar attitude measurement system using the method of claim 1, characterized in that: The system includes an electronic warehouse, a towing body, a linear array transducer element and a target. The electronic warehouse is arranged above the towing body, the linear array transducer element is connected to the bottom of the towing body, the target is arranged on the bottom of the water, the linear array transducer element is composed of a calibration hydrophone, an active sound source is arranged in the middle of the linear array transducer element, and a wireless calibration sound source is arranged in the middle of the target.

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