Vector hydrophone-based naval vessel propeller micro-Doppler model construction method

Abstract

The invention discloses a vector hydrophone-based naval vessel propeller micro-Doppler model construction method, and belongs to the field of underwater target identification methods. An existing target identification method based on micro Doppler has the problems that the real-time performance is poor, the quality of obtained data is poor, and a system cannot achieve integrated processing. The method comprises the following steps: setting the total scattering component of a submarine propeller as the linear sum of scattering echoes of each blade; designing a relative position relation between the vector hydrophone and a naval vessel propeller; solving the distance from the scattering point P to the vector hydrophone; solving a reflection echo expression of the scattering point P; solving a vector hydrophone echo signal of a single blade; solving a vector hydrophone echo of a single rotor; and carrying out modeling simulation on a single rotor wing according to the established micro-Doppler model of the naval vessel propeller. According to the method, the target detection and positioning capability is enhanced, the target identification and classification performance is improved, the influence of environmental interference is reduced, and the real-time performance and reliability of processing are enhanced.

Description

Technical Field

[0001] The invention relates to a method for constructing a micro-Doppler model of a ship propeller, and in particular to a method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone. Background Art

[0002] Micromotion first appeared in coherent laser vector hydrophones. Victor C. Chen of the U.S. Naval Research Laboratory first proposed the concepts of micromotion and micro-Doppler and introduced them into vector hydrophone observations. Micromotions are collectively referred to as vibrations, rotations, and accelerations of targets or target components other than the translation of the center of mass, and the Doppler frequency shift caused by target micromotion is called micro-Doppler. Based on this definition, Chen Xingyong and others from the National University of Defense Technology generalized micromotion as "a small non-uniform motion or motion component of a target or target component in the radial direction relative to a vector hydrophone (relative to the radial distance between the target and the vector hydrophone)". From the perspective of the Doppler effect, if a point target has non-uniform motion in the radial direction of the vector hydrophone, its Doppler changes with time, which is manifested as spectrum broadening; at the same time, targets often have complex non-rigid motion forms, and the relative motion of each mass element will also cause its echo spectrum to have side lobes or broadening, which is called the micro-Doppler effect. Micro-Doppler reflects the instantaneous characteristics of frequency and describes the instantaneous Doppler variation characteristics caused by micro-motion. Therefore, micro-Doppler is time-varying, that is, the frequency changes with time. Micro-motion phenomena are common in nature, such as the swinging of pedestrians' arms and limbs, the movement of the human heartbeat and chest during breathing, motors, tracked vehicles, armored vehicles and car wheels, helicopter rotors, the vibration (precession and nutation) of ballistic missile warheads, the bumping and swinging of ships, and the rotation of antennas. The vector hydrophone echo characteristics of micro-motion targets reflect the fine characteristics of the target, such as structural characteristics, electromagnetic scattering characteristics and motion characteristics, so they are of great significance for the detection and identification of space, air, ground targets and surface ships.

[0003] At present, foreign research institutions and universities, mainly the U.S. Naval Research Laboratory, the Canadian Defense Technology Research Center, the University of Texas, and the Nanyang Technological University of Singapore, have conducted relatively systematic research on the micro-Doppler of vector hydrophone targets, and gradually formed a research system from target modulation model, feature analysis and extraction to method verification and experimental measurement. In engineering applications, the micro-Doppler measurement vector hydrophone system has developed from a single Doppler measurement function to a measurement capability with both high Doppler resolution and high range resolution. The United States has always been in the international leading position in this area. In 2000, Philip Gat and others successfully developed a dual-pulse continuous wave laser vector hydrophone, which successfully detected the micro-Doppler signals of ground and air targets and used it for feature extraction, target recognition, and battlefield situation assessment. In 2001, the Georgia Institute of Technology in the United States used a continuous wave vector hydrophone to observe the micro-motion characteristics of vehicle targets and extract features, which has been applied to the development of automobile safety warning systems; in 2002, the THAAD GBR X-band vector hydrophone developed by the United States can accurately measure the micro-motion characteristics of ballistic missile warheads and identify real and fake warheads; in 2007, the University of Texas developed a micro-motion measurement vector hydrophone system with a multi-frequency continuous wave system with three transmission frequencies in the X-band, which can measure the distance while measuring micro-Doppler, collect and analyze the micro-Doppler characteristics of pedestrians, vehicles and animals in different maneuvers, and the results can be used for automatic target detection and identification. In view of the limited microwave band resources and expensive experimental equipment, in 2011, Alessio Baller et al. of the University of London in the United Kingdom used a frequency-agile ultrasonic vector hydrophone to collect micro-Doppler characteristics, which reduced the experimental cost, but due to the limitation that the generated signal is easily attenuated in the atmosphere, it can only be used for short-range detection, such as indoor and airport passenger monitoring.

[0004] In China, many scientific research institutions such as the National University of Defense Technology, Air Force Engineering University, the 23rd Institute of the Second Academy of China Aerospace, and Xidian University have carried out certain research in micro-Doppler, and have a certain research foundation in this regard. However, the research on micro-Doppler theory and technology is not yet mature, and the research content is mainly focused on the application research of micro-Doppler effect, including micro-Doppler feature modeling, micro-motion feature extraction, micro-motion target vector hydrophone SAR and ISAR imaging, etc. The research objects include high-speed moving targets, such as ground vehicles such as tanks, armored vehicles, missile launchers and other vibrating targets, sea surface corner reflectors, rotor targets represented by helicopters, precession and nutation targets represented by ballistic missiles, and non-rigid micro-motion targets such as pedestrians, etc. It can be seen that micro-Doppler has become a hot research topic at home and abroad.

[0005] In the field of underwater acoustic detection, there are also a large number of target micro-motions, such as the vibration of the ship hull, the rotation of the propeller, etc. These micro-motions will have a modulation effect on the echo signal, and generate an echo signal with micro-Doppler characteristics. However, these micro-Doppler characteristic signals have not yet been applied to the detection and identification of underwater targets. Therefore, the present invention mainly takes the rotation of the underwater target propeller as the object, and receives and analyzes the echo signal with micro-Doppler characteristics generated by the modulation of the active acoustic detection signal by the vector hydrophone.

[0006] Vector hydrophones can be divided into co-vibration type and pressure difference type vector hydrophones. Compared with sound pressure hydrophones that can only measure sound pressure, vector hydrophones can also use horizontal and vertical channels to better capture transverse and longitudinal wave information. The amount of information provided by a single vector hydrophone is equivalent to the information provided by a four-element sound pressure array, so a single vector hydrophone can complete the azimuth and pitch angle estimation of the sound source. Different mathematical combinations of sound pressure and vibration velocity can obtain different directivities. The alignment direction can be changed by electronic rotation. Combined with directivity, it can better suppress noise in other directions and isotropic noise, and realize the detection of weak underwater acoustic signals. The United States and Russia developed vector hydrophones earlier than other countries, and their research level is relatively ahead of other countries. In the 1940s, the United States developed a sound pressure gradient vector hydrophone. Since then, due to the international situation and scientific and technological progress, more and more countries have begun to conduct in-depth research on vector hydrophones, and high-sensitivity vector hydrophones have emerged. my country's research on vector hydrophones started a little later. It began to invest in research in the 1990s and developed a fixed shell type vector hydrophone. In 1998, my country conducted the first field experiment on vector hydrophones. In recent years, with the continuous development of hydrophone research and development technology, my country has successfully developed piezoresistive vector hydrophones and fiber-optic vector hydrophones.

[0007] Vector hydrophones have a natural advantage in DOA estimation. When the signal-to-noise ratio is low, the accuracy of the MUSIC algorithm will drop significantly. To solve this problem, Yuan Zhiyong et al. proposed a vector fourth-order cumulant algorithm, which can accurately estimate the target direction and is suitable for lower signal-to-noise ratio environments; the fourth-order cumulant direction-finding algorithm will undoubtedly greatly increase the amount of calculation; for the problem that the high-order cumulant algorithm has high complexity, a method uses the third-order tensor decomposition principle to propose a MUSIC algorithm based on second-order statistics, but this algorithm only does not suppress interference terms, so the accuracy of the algorithm is greatly affected by interference; in order to realize the multi-target sound source positioning of a single vector hydrophone, a method extracts useful components from the signal through a vector hydrophone to increase the rank of the vector matrix. This method realizes the multi-target sound source positioning of high-order cumulants. Based on the MUSIC algorithm, Shi Jie et al. proposed a beam-domain broadband focusing MUSIC algorithm, which not only improves robustness but also reduces the amount of calculation to a certain extent. Vector hydrophones are rarely used in deep-sea positioning. Sun Mei and others from the Institute of Acoustics of the Chinese Academy of Sciences analyzed the propagation characteristics of sound lines when received at great depths, used an average sound intensity meter to estimate the azimuth and grazing angle, and based on the changing relationship between the arrival angle and distance, proposed a passive sound source ranging method based on vector hydrophones.

[0008] In summary, there have been many achievements in target recognition based on micro-Doppler, but the following problems still exist:

[0009] 1. Algorithm complexity: Current micro-Doppler target recognition algorithms often require a lot of computing resources and time to complete processing. This limits the real-time performance and efficiency in practical applications. Therefore, further research on more efficient algorithms is needed to improve the speed and accuracy of target recognition.

[0010] 2. Unstable data quality: Due to the complexity of the marine environment, the data obtained by the vector hydrophone is affected by ocean currents, waves and other environmental factors, resulting in unstable data quality. More effective methods are needed to deal with these interferences.

[0011] 3. Integration processing of corresponding platforms: There is no corresponding integration processing method for underwater ships. The integration of hardware and software systems needs to take into account issues such as interfaces and communication protocols between multiple modules, which puts high demands on system design and implementation. Therefore, in-depth research and development are needed to achieve smooth system integration. Summary of the invention

[0012] The purpose of the present invention is to solve the problems of poor real-time performance, poor quality of acquired data and inability of the system to achieve integrated processing in the existing target recognition method based on micro-Doppler, and to propose a method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone.

[0013] The above purpose is achieved through the following technical solutions:

[0014] A method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone is implemented by the following steps:

[0015] Step 1: Assume that each propeller blade is an independent scattering center, and each scattering center is independent of each other in the acoustic radiation area; the total scattering component of the submarine propeller is the linear sum of the scattered echoes of each blade;

[0016] Step 2: Design the relative position relationship between the vector hydrophone and the ship propeller;

[0017] Step 3: Calculate the distance from the scattering point P to the vector hydrophone;

[0018] Step 4: Obtain the expression of the reflected echo of the scattering point P;

[0019] Step 5, obtaining the vector hydrophone echo signal of a single blade;

[0020] Step 6: Obtain the vector hydrophone echo of a single rotor;

[0021] Step 7: Based on the micro-Doppler model of the ship propeller established above, a single rotor is modeled and simulated.

[0022] Furthermore, the process of designing the relative position relationship between the vector hydrophone and the ship propeller described in step 2 is specifically as follows: the vector hydrophone and the rotor center are located at the origin of the fixed coordinate system (X, Y, Z) and the own coordinate system (x, y, z), respectively; the initial distance from the rotor center to the vector hydrophone is R0, the height is h, the azimuth angle relative to the line of sight of the vector hydrophone is α, the pitch angle is β, the moving speed is v, and the rotor speed is ω r ; P is a scattering point on the blade, and its distance to the rotor center O is OP = l p , the distance from the blade root to point O is L1, the distance from the blade tip to point O is L2, and the effective blade length L = L2-L1; the initial phase at point P is θ0, and the phase angle at time t is θ t =θ0+Ωt, Ω is the scalar angular velocity.

[0023] Furthermore, the process of obtaining the distance from the scattering point P to the vector hydrophone in step 3 is specifically as follows:

[0024] The position of the scattering point P in the reference coordinate system at time t is (l p cosθ t , l p sinθ t , 0), the distance from point i to the vector hydrophone is R t=R0+νt, the coordinates of the rotor center O in the fixed coordinate system are (R, cosβcosα, R t cosβsinα, R t sinβ), the distance from the scattering point P to the vector hydrophone is:

[0025]

[0026] Furthermore, the process of obtaining the expression of the reflected echo of the scattering point P described in step 4 is specifically as follows:

[0027] The vector hydrophone echo reflected from the scattering point P is:

[0028]

[0029] Combined with formula (3-1), the phase function is:

[0030]

[0031] The expression of the reflected echo at the scattering point P is:

[0032]

[0033] Furthermore, the process of obtaining the vector hydrophone echo signal of a single blade in step 5 is specifically as follows:

[0034] Remove the carrier frequency of the echo signal and conduct a p The vector hydrophone echo signal of a single blade can be obtained by integration:

[0035]

[0036] Furthermore, the process of obtaining the vector hydrophone echo of a single rotor described in step 6 is specifically as follows:

[0037] Assuming that each rotor consists of N blades, the vector hydrophone echo of a single rotor is:

[0038]

[0039] The beneficial effects of the present invention are:

[0040] The method of the invention enhances the target detection and positioning capabilities, and improves the detection and positioning capabilities of the vector hydrophone system for the target by utilizing the micro-motion Doppler characteristics of the echo signal of the ship propeller. By extracting information such as the speed, direction and frequency of the target, the position and motion state of the target can be determined more accurately.

[0041] The method of the present invention improves the target recognition and classification performance. The micro-Doppler signal provides the motion characteristics of the target, which can be used to distinguish different types of targets. The characteristic parameters of the target are extracted and applied to the classification and recognition of the target, thereby improving the accuracy and reliability of target recognition.

[0042] The method of the present invention reduces the influence of environmental interference. The vector hydrophone system may be subject to various interferences in a complex underwater environment, such as water flow noise, scattering noise, etc. The data processing algorithm is designed and optimized to reduce the influence of environmental interference and improve the anti-interference ability of the system.

[0043] The method of the present invention enhances the real-time and reliability of processing. By combining the vector hydrophone with the stm32 hardware platform, the ship echo signal is received and processed in real time and the processed results are stored. It is planned to transmit the processed results to the receiving unit by wireless communication to achieve real-time processing and analysis.

[0044] This paper takes underwater ship target recognition as the research background, and conducts research on the micro-motion feature extraction and estimation technology of ship targets under motion based on vector hydrophone. First, the modulation effect of the vector hydrophone echo of the micro-motion target is systematically studied. On this basis, a method for extracting micro-Doppler features is proposed, and data is exported through a single vector hydrophone plus an acquisition module. The results are obtained by processing these data on the stm32 hardware platform, which are specifically divided into the following parts:

[0045] (I) First, the physical principle of the micro-Doppler effect and the theoretical derivation of the micro-Doppler frequency shift are discussed. Then, a micro-motion model of the submarine propeller is established based on the point scattering model. At the same time, a cone micro-motion model is established for the flow field regulator, and an effective method for extracting micro-Doppler features from the rotor micro-Doppler echo signal is studied. This paper first mathematically models the vibrating and rotating targets, and derives the echo models of the propeller rotor and the cone. On this basis, the underwater echo signals of the ship propeller and the flow field regulator are simulated and analyzed.

[0046] (II) Micro-Doppler feature extraction based on commonly used time-frequency analysis methods. Non-parametric time-frequency analysis and parametric time-frequency analysis are introduced, and the short-time Fourier transform, short-time Fourier transform, and wavelet transform theoretical derivation and simulation experiments are carried out. The simulation results are compared and analyzed, and the advantages and disadvantages of the various time-frequency analysis methods in micro-Doppler feature extraction are summarized.

[0047] (III) The mathematical model of vector hydrophone and two important methods of azimuth estimation of single vector hydrophone are introduced, and the basic principle of positioning by single vector hydrophone is also explained. Two azimuth estimation methods of vector hydrophone, average sound intensity and complex sound intensity, are introduced, and the performance of azimuth estimation method and azimuth estimation of single vector hydrophone are analyzed, and the signal of ship target is collected by single vector hydrophone.

[0048] (iv) Processing the real-time echo signal received by the hydrophone through the stm32 hardware based on the ARM platform, receiving the water acoustic signal received by the hydrophone through the hardware device, and performing real-time processing on the hardware and storing the processed signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is a flow chart of the method of the present invention;

[0050] Figure 2 The present invention is a diagram showing the relative position relationship between the vector hydrophone and the propeller of a ship. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are 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 are within the scope of protection of the present invention. Specific implementation method one:

[0053] A method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this embodiment is as follows: Figure 1 As shown, the method is implemented by the following steps:

[0054] Step 1: Submarine propellers are generally made of metal or composite materials and have a high reflection coefficient. Different blades differ in shape and curvature, and may bend and crease during rotation. However, in the study of underwater signal processing, the influence of these factors is usually temporarily ignored. For traditional underwater narrow-band low-resolution sonar systems, the propeller components of submarines are generally in the acoustic radiation area, so the point scattering model can be used to analyze its acoustic scattering.

[0055] Assume that each propeller blade is an independent scattering center, and each scattering center is independent of each other in the acoustic radiation area; therefore, the total scattering component of the submarine propeller is regarded as the linear sum of the scattered echo of each blade;

[0056] Step 2: Design the relative position relationship between the vector hydrophone and the ship propeller;

[0057] Step 3: Calculate the distance from the scattering point P to the vector hydrophone;

[0058] Step 4: Obtain the expression of the reflected echo of the scattering point P;

[0059] Step 5, obtaining the vector hydrophone echo signal of a single blade;

[0060] Step 6: Obtain the vector hydrophone echo of a single rotor;

[0061] Step 7: Based on the micro-Doppler model of the ship propeller established above, a single rotor is modeled and simulated. Specific implementation method 2:

[0063] Different from the first embodiment, in the method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this embodiment, the process of designing the relative position relationship between the vector hydrophone and the ship propeller in step 2 is specifically as follows: Figure 2 As shown, the vector hydrophone and the rotor center are located at the origin of the fixed coordinate system (X, Y, Z) and the origin of the rotor coordinate system (x, y, z), respectively; the initial distance from the rotor center to the vector hydrophone is R0, the height is h, the azimuth angle relative to the line of sight of the vector hydrophone is α, the pitch angle is β, the moving speed is v, and the rotor speed is ω r ; P is a scattering point on the blade, and its distance to the rotor center O is OP = l p , the distance from the blade root to point O is L1, the distance from the blade tip to point O is L2, and the effective blade length L = L2-L1; the initial phase at point P is θ0, and the phase angle at time t is θ t =θ0+Ωt, Ω is the scalar angular velocity. Specific implementation method three:

[0065] Different from the second specific implementation mode, in the method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this implementation mode, the process of obtaining the distance from the scattering point P to the vector hydrophone in step 3 is specifically as follows:

[0066] The position of the scattering point P in the reference coordinate system at time t is (l p cosθ t , l p sinθ t , 0), the distance from point O to the vector hydrophone is R t =R0+vt, the coordinates of the rotor center O in the fixed coordinate system are (R, cosβcosα, R t cosβsinα, R t sinβ), the distance from the scattering point P to the vector hydrophone is:

[0067] Specific implementation method four:

[0069] Different from the third specific implementation mode, in the method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this implementation mode, the process of obtaining the expression of the reflected echo of the scattering point P in step 4 is specifically as follows:

[0070] The vector hydrophone echo reflected from the scattering point P is:

[0071]

[0072] Combined with formula (3-1), the phase function is:

[0073]

[0074] The expression of the reflected echo at the scattering point P is:

[0075] Specific implementation method five:

[0077] Different from the fourth specific implementation mode, in the method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this implementation mode, the process of obtaining the vector hydrophone echo signal of a single blade in step 5 is specifically:

[0078] Remove the carrier frequency of the echo signal and conduct a p The vector hydrophone echo signal of a single blade can be obtained by integration:

[0079] Specific implementation method six:

[0081] Different from the fifth specific implementation mode, in the method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone in this implementation mode, the process of obtaining the vector hydrophone echo of a single rotor described in step 6 is specifically:

[0082] Assuming that each rotor consists of N blades, the vector hydrophone echo of a single rotor is:

[0083]

[0084] The embodiments of the present invention disclose preferred embodiments, but are not limited thereto. A person skilled in the art can easily understand the spirit of the present invention based on the above embodiments and make different extensions and changes. However, as long as they do not deviate from the spirit of the present invention, they are all within the protection scope of the present invention.

Claims

1. A method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone, characterized in that: The method is implemented by the following steps: Step 1: Assume that each propeller blade is an independent scattering center, and each scattering center is independent of each other in the acoustic radiation area; the total scattering component of the submarine propeller is the linear sum of the scattered echoes of each blade; Step 2: Design the relative position relationship between the vector hydrophone and the ship propeller; Step 3: Calculate the distance from the scattering point P to the vector hydrophone; Step 4: Obtain the expression of the reflected echo of the scattering point P; Step 5, obtaining the vector hydrophone echo signal of a single blade; Step 6: Obtain the vector hydrophone echo of a single rotor; Step 7: Based on the micro-Doppler model of the ship propeller established above, a single rotor is modeled and simulated.

2. The method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone according to claim 1, characterized in that: The process of designing the relative position relationship between the vector hydrophone and the ship propeller described in step 2 is specifically as follows: the vector hydrophone and the rotor center are located at the origin of the fixed coordinate system (X, Y, Z) and the own coordinate system (x, y, z), respectively; the initial distance from the rotor center to the vector hydrophone is R0, the height is h, the azimuth angle relative to the line of sight of the vector hydrophone is α, the pitch angle is β, the moving speed is v, and the rotor speed is ω r ; P is a scattering point on the blade, and its distance to the rotor center O is OP = l p , the distance from the blade root to point O is L1, the distance from the blade tip to point O is L2, and the effective blade length L = L2-L1; the initial phase at point P is θ0, and the phase angle at time t is θ t =θ0+Ωt, Ω is the scalar angular velocity.

3. The method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone according to claim 2, characterized in that: The process of obtaining the distance from the scattering point P to the vector hydrophone described in step 3 is specifically as follows: The position of the scattering point P in the reference coordinate system at time t is (l p cosθ t , l p sinθ t , 0), the distance from point O to the vector hydrophone is R t =R0+νt, the coordinates of the rotor center O in the fixed coordinate system are (R, cosβcosα, R t cosβsinα, R t sinβ), the distance from the scattering point P to the vector hydrophone is:

4. The method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone according to claim 3, characterized in that: The process of obtaining the expression of the reflected echo of the scattering point P described in step 4 is specifically as follows: The vector hydrophone echo reflected from the scattering point P is: Combined with formula (3-1), the phase function is: The expression of the reflected echo at the scattering point P is:

5. The method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone according to claim 4, characterized in that: The process of obtaining the vector hydrophone echo signal of a single blade in step 5 is specifically as follows: Remove the carrier frequency of the echo signal and conduct a p The vector hydrophone echo signal of a single blade can be obtained by integration:

6. The method for constructing a micro-Doppler model of a ship propeller based on a vector hydrophone according to claim 5, characterized in that: The process of obtaining the vector hydrophone echo of a single rotor described in step 6 is specifically as follows: Assuming that each rotor consists of N blades, the vector hydrophone echo of a single rotor is:

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