A passive guidance-based real-time optical tracking method and system for moving targets

Abstract

The present application relates to the technical field of image processing, in particular to a kind of real-time optical tracking method and system of moving target based on passive guidance.The approximate coordinates of moving target are obtained by passive direction finding station;And according to the approximate coordinates, control laser illumination unit to light moving target body, utilize binocular camera unit to carry out image acquisition and visual analysis to moving target, to obtain the position change of moving target;Combining the position change of moving target, determine the trajectory pose of moving target.Using call camera unit, the whole tracking of moving target is carried out, and the flight state of moving target collected is transmitted to host computer in real time for display.The present application realizes real-time positioning of moving target by the fusion mode of passive direction finding station and binocular optical system, realizes real-time accurate positioning of moving target in the case of building, vegetation dense and low visibility.

Description

Technical Field

[0001] This invention relates to the field of image processing technology, and specifically to a method and system for real-time optical tracking of moving targets based on passive guidance. Background Technology

[0002] With the widespread application of moving target technology in logistics, urban security, and emergency rescue, continuous and accurate tracking and monitoring of low-altitude, slow-moving, small moving targets, namely low-altitude, slow-moving, small drones, has become a key technological requirement. These moving targets typically fly at low altitudes, have small radar cross-sections, and often operate in areas with dense buildings and vegetation, posing a significant challenge to traditional single-sensor tracking solutions.

[0003] Existing technologies primarily rely on single sensor sources such as lidar, visible light cameras, or radio detection, all of which have inherent limitations: lidar has limited penetration through non-rigid obstructions such as leaves, rain, and fog, and its laser beam is easily absorbed or scattered, leading to a sharp drop in the signal-to-noise ratio (SNR) of moving target point clouds; visible light cameras suffer severe image quality degradation at night or in smoky environments, with the SNR potentially dropping below 5 dB, and the confidence level of the tracking algorithm drops by more than 60% when the obscured area of ​​the moving target exceeds 30%; while single radio detection schemes offer some penetration, their positioning accuracy is typically only at the hundred-meter level, making it difficult to meet the requirements of high-precision trajectory tracking. Furthermore, electromagnetic interference, unstable GPS signals, and background light noise in complex urban environments further exacerbate tracking errors, resulting in discontinuous and easily interrupted moving target trajectories. While current attempts at multimodal fusion exist, they largely remain at the level of simple combination, failing to fully coordinate data from different sensors in time and space, resulting in a lack of end-to-end optimization, insufficient dynamic moving target interaction modeling, and low resource efficiency, making it difficult to simultaneously achieve both penetration and visual accuracy in complex obstructed environments. Summary of the Invention

[0004] To address the problem that existing technologies relying on a single sensor source struggle to penetrate obstacles and simultaneously acquire high-precision visual details in complex, obstructed environments, leading to discontinuous and easily interrupted tracking trajectories for moving targets, the present invention aims to provide a real-time optical tracking method and system for moving targets based on passive guidance. This method obtains the approximate coordinates of the moving target through a passive direction finding station, controls a laser illumination unit to increase the illumination brightness of the approximate coordinate area where the moving target is located, and combines multiple sets of positional changes of the moving target to track the target. This enables real-time and accurate positioning of the moving target in situations where it is obstructed by buildings, dense vegetation, or in low-visibility environments.

[0005] Specifically, on the one hand, the present invention provides a real-time optical tracking method for moving targets based on passive guidance, which includes the following steps: S1. Passive Direction Finding Guidance: By using at least two passive direction finding stations to network and cross-locate the radio signals emitted by a moving target, the approximate coordinates of the moving target are obtained. Specifically: ; ; Where D is the straight-line distance between the two passive direction finding stations; The azimuth angle of the passive direction finding station A. The azimuth angle of the passive direction finding station B; S2. Moving target recognition and tracking: Based on approximate coordinates, control the laser illumination unit to rotate toward the moving target and illuminate the approximate coordinate area where the moving target is located; S3. Using the two cameras of the binocular camera unit to acquire image information of the moving target, the acquired image information of the moving target is used to calculate the disparity of the moving target in the images of the two cameras and the system calibration parameters to obtain the three-dimensional coordinates and pose of the moving target in the measurement coordinate system in real time. The specific method for obtaining the three-dimensional coordinates of the moving target in the measurement coordinate system is as follows: obtain the pixel coordinates of the center point of the moving target, and based on the pixel coordinates of the center point of the moving target in the two cameras, calculate the three-dimensional coordinates of the moving target in the measurement coordinate system using the principle of triangulation; the specific method for solving the x-coordinate and y-coordinate of the three-dimensional coordinates of the center point of the moving target is as follows: ; ; in, Let A be the pixel coordinates of the center point of the moving target of camera A. Let the pixel coordinates be the center point of the moving target of camera B. The x and y coordinates of the three-dimensional coordinates of the center point of the moving target; S4. Moving Target Status Monitoring: The portable workstation unit combines multiple sets of position changes of the moving target to determine the trajectory and pose of the moving target; and calls the binocular camera unit to track the moving target throughout the entire process, and transmits the collected flight status of the moving target to the portable workstation unit, thereby realizing real-time monitoring of the moving target's status.

[0006] Preferably, step S1 specifically includes: Signal interception and identification: At least two passive direction finding stations are used to capture radio signals emitted by moving targets, and the frequency and modulation characteristics of the radio signals are analyzed to distinguish moving target signals from interference signals; Direction finding calculation: Obtain azimuth data from different passive direction finding stations through network detection, and filter and verify the azimuth data to remove outliers with large errors; Calculation of moving target coordinates: Based on the verified azimuth data and coordinates of the direction finding station, after time synchronization calibration, the approximate coordinates of the moving target are obtained through the cross-positioning algorithm.

[0007] Preferably, the azimuth angle of the passive direction finding station A is... The azimuth angle of passive direction finding station B The calculation is performed using the following formula: ; ; in, The original azimuth angle of the passive direction finding station A. This is the original azimuth angle of the passive direction finding station B. The static calibration error of passive direction finding station A. This represents the static calibration error of the passive direction finding station B.

[0008] Preferably, the method for determining the pixel coordinates of the moving target center point in step S3 for cameras A and B is as follows: Set a grayscale threshold T, binarize the difference image, and determine the pixel coordinates of the moving target center point. The calculation formula for the pixel coordinates of the moving target center point is: ; in, These are the pixel coordinates of the image; , respectively, are the gray values ​​of the image at (x,y) at time t and time t-1; The grayscale value is the value of the difference image.

[0009] Preferably, the control of the laser illumination unit to rotate toward the moving target in step S2 is as follows: read the calibration coordinates of turntable T1 and turntable T2, obtain the initial azimuth angles of the two turntables, add the initial azimuth angles to the real-time angles of the corresponding passive direction finding stations to obtain the rotation control angles, quantize the rotation control angles into integers, assemble data frames in the format of frame header + address code + quantized angle + check bit + frame tail, and send the data frames to the turntable controller through the RS-422 serial port.

[0010] In a second aspect, the present invention provides a system for implementing a method for real-time optical tracking of moving targets based on passive guidance, comprising: A passive direction finding station, including an antenna array, a multi-channel receiver, a signal processor, and a portable workstation unit, is used to detect and identify moving target signals. Through multi-station cross-positioning, it monitors the radio spectrum, analyzes the frequency, modulation characteristics, and intensity of characteristic signals, and obtains the approximate coordinates of the moving target. The binocular camera unit includes an image acquisition module, a time synchronization module, an RTK calibration module, and a data transmission module, which are used to acquire image data of moving targets and obtain the three-dimensional coordinates and pose of the moving targets; The laser illumination unit includes a laser illumination unit and a motorized pan-tilt unit. The laser illumination unit is communicatively connected to the passive direction finding station and the binocular camera unit to illuminate the approximate coordinate area where the moving target is located. The camera unit is used to track the moving target throughout its entire journey under the tracking and alignment of the turntable, and transmit video data information to the industrial control computer in real time for display. The portable workstation unit is used for system setup, control, data post-processing, and real-time display of the flight status and trajectory information of moving targets.

[0011] Preferably, the antenna array of the passive direction finding station is used to intercept the moving target signal, and amplify and convert the received signal to an intermediate frequency signal; the multi-channel receiver is used to receive the antenna and channel output signals; the signal processor performs signal detection and parameter estimation on the intermediate frequency signal to obtain the directional characteristic parameters of the moving target, and sends them to the portable workstation unit through the communication transmission network; the portable workstation unit fuses and cross-locates the parameters of multiple direction finding stations.

[0012] Preferably, the image acquisition module of the binocular camera unit includes two sets of cameras and two sets of optical lenses, which can acquire two sets of 2D coordinates of the moving target.

[0013] Preferably, the timing synchronization module of the binocular camera unit uses B-code timing to achieve synchronization and high-precision time measurement between the two cameras; the RTK calibration module, combined with the Global Positioning System and differential GPS technology, can provide the system with centimeter-level calibration results for moving targets in real time.

[0014] Preferably, the laser illumination unit includes two sets of laser illumination groups and two motorized pan-tilt units, enabling long-distance continuous monitoring of moving targets within a 1-kilometer range.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention achieves coarse positioning of moving targets through a network of passive direction finding stations, thereby guiding a dual-optical system for precise positioning. It overcomes the contradiction of a single sensor being "invisible" or "inaccurate" in complex environments, significantly improves tracking continuity in a spatial scanning area with a radius of 1km and a vertical height of 50m, and in scenarios such as gaps between buildings and light vegetation obstruction, and significantly reduces the trajectory interruption rate.

[0016] Passive direction finding provides approximate coordinates that are resistant to interference, while binocular vision improves positioning accuracy to the centimeter level, for example, with an error of <10cm, through stereo matching and parallax calculation. This effectively solves the positioning drift problem caused by multipath effects in cities and canyons when using a single satellite navigation GNSS, and achieves high-precision pose estimation.

[0017] By employing reflective targets and active laser illumination, the contrast between moving targets and the background is significantly enhanced, increasing the success rate of moving target recognition by approximately 40% under adverse weather conditions such as low light and fog, and effectively suppressing ambient light noise and background interference.

[0018] The timing synchronization module ensures the consistency of passive direction finding and optical acquisition, controlling system latency jitter to the millisecond level. Combined with motion trend prediction algorithms, it enables rapid re-acquisition after a brief occlusion of a moving target, significantly improving the trajectory association success rate.

[0019] The system boasts high integration and flexible deployment. It enables multi-station data fusion and real-time display via portable workstations, making it suitable for scenarios such as urban patrol and key area monitoring, and providing reliable technical support for the control of moving targets. Attached Figure Description

[0020] Figure 1 This invention relates to the working principle of a passive guided optical tracking system for real-time optical tracking of moving targets based on a passive guided method and system. Figure 2 This is a block diagram illustrating the principle of the passive direction finding station in the real-time optical tracking method and system for moving targets based on passive guidance, as described in this invention. Figure 3 This invention provides a motion target RTK calibration process for a passive-guided real-time optical tracking method and system. Figure 4 The measurement layout of the image acquisition module of the present invention is shown in the image acquisition module of the real-time optical tracking method and system for moving targets based on passive guidance. Figure 5 This is a schematic diagram of the laser illumination range of the real-time optical tracking method and system for moving targets based on passive guidance, as presented in this invention. Detailed Implementation

[0021] In a first aspect, the present invention provides a real-time optical tracking method for moving targets based on passive guidance, which includes the following steps: S1. Passive Direction Finding Guidance: By using at least two passive direction finding stations to network and cross-locate the radio signals emitted by a moving target, the approximate coordinates of the moving target are obtained. Specifically: ; ; Where D is the straight-line distance between the two passive direction finding stations; The azimuth angle of the passive direction finding station A. The azimuth angle of the passive direction finding station B.

[0022] The azimuth angle of passive direction finding station A The azimuth angle of passive direction finding station B The calculation is performed using the following formula: ; ; in, The original azimuth angle of the passive direction finding station A. This is the original azimuth angle of the passive direction finding station B. The static calibration error of passive direction finding station A. This represents the static calibration error of the passive direction finding station B.

[0023] Time synchronization calibration is performed during data acquisition: a unified time reference is obtained based on GPS / BeiDou time synchronization.

[0024] Δt = |TimeA - TimeB|; In the formula: TimeA and TimeB are the data acquisition timestamps of passive direction finding stations A and B; if Δt > 10ms, discard the data of this group and re-acquire; after synchronization, the unified timestamp is Time = max(TimeA, TimeB).

[0025] S2. Moving Target Recognition and Tracking: Based on approximate coordinates, control the laser illumination unit to rotate towards the moving target and illuminate the approximate coordinate area where the moving target is located. Specifically, controlling the rotation of the laser illumination unit towards the moving target in step S2 involves: reading the calibration coordinates of turntables T1 and T2, obtaining the initial azimuth angles of the two turntables, and then comparing these initial azimuth angles with the real-time angles of the corresponding passive direction finding stations, i.e., with the direction finding azimuth angles of passive direction finding station A. The azimuth angle of passive direction finding station B The rotation control angle is obtained by summing the values ​​and quantizing it into an integer. A data frame is then assembled in the format of frame header + address code + quantized angle + check bit + frame tail, and sent to the turntable controller via RS-422 serial port. The turntable controls the laser to emit laser pulses, illuminating the coarse positioning spatial domain of the moving target. The laser pulse emission frequency is strictly consistent with the binocular camera's acquisition frequency, ensuring that each image frame corresponds to the laser illumination moment. Simultaneously, the laser power needs to be adjusted according to the monitoring distance and ambient light intensity to ensure a significant grayscale difference between the moving target and the background, improving the success rate of frame difference contour extraction.

[0026] S3. Using the two cameras of the binocular camera unit to acquire image information of the moving target, the acquired image information of the moving target is used to calculate the disparity of the moving target in the images of the two cameras and the system calibration parameters to obtain the three-dimensional coordinates and pose of the moving target in the measurement coordinate system in real time. The specific method for obtaining the three-dimensional coordinates of the moving target in the measurement coordinate system is as follows: obtain the pixel coordinates of the center point of the moving target, and based on the pixel coordinates of the center point of the moving target in the two cameras, calculate the three-dimensional coordinates of the moving target in the measurement coordinate system using the principle of triangulation; the specific method for solving the x-coordinate and y-coordinate of the three-dimensional coordinates of the center point of the moving target is as follows: ; ; in, Let A be the pixel coordinates of the center point of the moving target of camera A. Let the pixel coordinates be the center point of the moving target of camera B. These are the x and y coordinates of the three-dimensional coordinates of the center point of the moving target. Since the moving target is a low-altitude economic zone, the Z-axis coordinate can be directly obtained.

[0027] In step S3, the method for determining the pixel coordinates of the moving target center point of cameras A and B is as follows: Set a grayscale threshold T, binarize the difference image, and then calculate the pixel coordinates of the moving target center point. The calculation formula for the pixel coordinates of the moving target center point is: ; in, These are the pixel coordinates of the image; , respectively, are the gray values ​​of the image at (x,y) at time t and time t-1; The grayscale value is the value of the difference image.

[0028] S4. Moving Target Status Monitoring: The portable workstation unit combines multiple sets of position changes of the moving target to determine the trajectory and pose of the moving target; and calls the binocular camera unit to track the moving target throughout the entire process, and transmits the collected flight status of the moving target to the portable workstation unit, thereby realizing real-time monitoring of the moving target's status.

[0029] In a second aspect, the present invention provides a system for implementing a method for real-time optical tracking of moving targets based on passive guidance, comprising: A passive direction finding station, comprising an antenna array, a multi-channel receiver, a signal processor, and a portable workstation unit, is used to detect and identify moving target signals. Through multi-station cross-location, it monitors the radio spectrum, analyzes the frequency, modulation characteristics, and intensity of characteristic signals to obtain the approximate coordinates of the moving target and perform coarse positioning. The antenna array of the passive direction finding station intercepts the moving target signal, amplifies and converts the received signal, down-converting it to an intermediate frequency (IF) signal. The multi-channel receiver receives the antenna and channel output signals. The signal processor performs signal detection and parameter estimation on the IF signal to obtain the directional characteristic parameters of the moving target, and transmits them to the portable workstation unit via a communication network. The portable workstation unit fuses the parameters from multiple direction finding stations and performs cross-location.

[0030] The binocular camera unit includes an image acquisition module, a timing synchronization module, an RTK calibration module, and a data transmission module. It is used to acquire image data of moving targets and calculate the three-dimensional coordinates and pose of the moving targets through binocular vision measurement. The image acquisition module of the binocular camera unit includes two sets of cameras and two sets of optical lenses, which can acquire two sets of 2D coordinates of the moving targets. The timing synchronization module of the binocular camera unit uses B-code timing to achieve synchronization and high-precision time measurement between the two cameras. The RTK calibration module combines Global Positioning System (GPS) and Differential GPS technology to provide the system with centimeter-level calibration results of moving targets in real time.

[0031] The laser illumination unit, including a laser illumination unit and an electric pan-tilt unit, is communicatively connected to a passive direction finding station and a binocular camera unit to illuminate the approximate coordinate area where the moving target is located. The laser illumination unit includes two sets of laser illumination groups and two electric pan-tilt units, enabling long-distance continuous monitoring of moving targets within a 1-kilometer range.

[0032] The camera unit is used to track the moving target throughout its entire journey under the tracking and alignment of the turntable, and transmit video data information to the industrial control computer in real time for display.

[0033] The portable workstation unit is used for system setup, control, data post-processing, and real-time display of the flight status and trajectory information of moving targets.

[0034] like Figure 1 As shown, this embodiment provides a method for identifying and tracking moving targets based on a passive direction finding station and binocular recognition, including the following steps: S1, Passive Direction Finding Guidance: By using at least two passive direction finding stations to network and cross-locate the radio signals emitted by the moving target, the approximate coordinates of the moving target can be obtained. In a preferred embodiment, the guidance information includes, for example, the grid coordinates of the moving target such as a drone or small aircraft, the approximate direction of movement of the moving target, and the estimated speed of movement.

[0035] S11. Signal interception and identification: Using direction finding equipment to capture the radio signals radiated by moving targets, and analyzing the frequency and modulation characteristics of the signals to distinguish moving target signals from interference signals.

[0036] S12. Direction finding calculation: Obtain azimuth data from different direction finding stations through network detection, filter, verify, and eliminate outliers with large errors in the direction finding data to improve positioning accuracy.

[0037] S13. Calculate the coordinates of the moving target: Based on the verified azimuth angle data and the coordinates of the direction finding station, obtain the approximate coordinates of the moving target through a cross-positioning algorithm. Let the coordinates of direction finding station S1 be (x1, y1), and the azimuth angle be... 1; Let the coordinates of the direction finding station S2 be (x2, y2), and the direction finding azimuth angle be... 2. The moving target P(x, y) satisfies: 1 = (y - y1) / (x - x1); 2 = (y - y²) / (x - x²); Simultaneously calculate the coordinates (x, y) of the moving target.

[0038] S2. Moving target recognition and tracking: It receives guidance information, controls the laser illumination unit to light up the moving target body, and uses the binocular camera unit to perform image acquisition and visual analysis on the moving target body to obtain the three-dimensional coordinates and pose of the moving target in the measurement coordinate system; S21. Laser illumination: Based on the guidance information obtained by the passive direction finding station, the laser illumination unit is controlled to synchronously illuminate the moving target; as a more preferred implementation, the effect of laser illumination can be significantly improved by placing the passive reflective target on the surface of the moving target body by adhesive.

[0039] S22. Stereo Vision Measurement: The binocular camera unit is invoked to generate matching image pairs using the moving target image information acquired by the camera. Based on the binocular vision measurement principle, the three-dimensional coordinates and pose of the moving target in the measurement coordinate system are obtained in real time by calculating the disparity of the moving target in the images of the two cameras and the system calibration parameters.

[0040] S3. Moving target status monitoring: The host computer combines the positional changes of multiple moving targets to determine the trajectory and pose of the moving targets. Furthermore, by utilizing camera units, the moving targets are tracked throughout their flight, and the collected flight status data is transmitted in real-time as a video stream to the host computer for display. This facilitates ground personnel's observation of the status of aerial targets and enables timely decision-making.

[0041] On the other hand, the present invention provides a system for real-time optical tracking of moving targets based on passive guidance, which includes a passive direction finding station, a binocular camera unit, a laser illumination unit, and a workstation unit.

[0042] Passive direction finding station: Passive direction-finding stations are devices used to detect and identify moving target signals. Through multi-station cross-positioning, monitoring of the radio spectrum, and analysis of the frequency, modulation characteristics, and intensity of characteristic signals, they obtain the approximate coordinates of the moving target and perform coarse positioning. Specifically, for example... Figure 2 As shown, this unit includes an antenna array, a multi-channel receiver, a signal processor, a control host, and a GPS compass.

[0043] The array antenna is used to intercept moving target signals, amplify and convert the received signals, down-converting them to intermediate frequency (IF) signals. A multi-channel receiver receives signals from the antenna and channel outputs. The signal processor performs signal detection and parameter estimation on the IF signals to obtain the directional characteristic parameters of the moving target, and sends them to the fusion center server via a communication network. The control host fuses and cross-locates parameters from multiple direction-finding stations to achieve the detection, localization, and tracking of moving targets.

[0044] Binocular camera unit: The binocular camera unit is used to acquire image data of moving targets and calculates high-precision 3D coordinates and pose of the moving targets using the binocular vision measurement principle. Specifically, this unit includes an image acquisition module, a time synchronization module, an RTK calibration module, and a data transmission module.

[0045] The image acquisition module includes two sets of cameras and two sets of optical lenses, which can acquire two sets of 2D coordinates of a moving target; for example... Figure 4 As shown, in the preferred embodiment of this example, the camera is selected from the Thousand Eyes Wolf G1501 series, and the optical lens is an optical 100mm F / 2.8 CA-Dreamer Macro 2X optical lens. At this time, the baseline distance is 800 meters, the object distance is 1000 meters, the binocular field of view is about 200 meters, the field of view angle is about 10°, and the angle between the baseline and the optical axis is about 68°.

[0046] The time synchronization module uses B-code time synchronization to achieve synchronization and high-precision time measurement between two cameras. The working principle of B-code time synchronization is as follows: In GPS signals, each satellite transmits its own B-code, containing the satellite's accurate position and time information. By receiving B-codes from three or more GPS satellites, the current time can be calculated and used as a reference clock. By receiving and decoding the B-code signals emitted by the reference clock, time synchronization and accuracy can be achieved.

[0047] The RTK calibration module combines GNSS and differential GPS technologies to calibrate the external parameters of two cameras; for example... Figure 3 The calibration process shown is divided into two working routes that are carried out simultaneously: a binocular high-speed camera captures moving targets with precise positioning function in real time, and the returned data is used for inversion calibration.

[0048] The data transmission module adopts fiber optic transmission, using a QSFP+ (40G) optical module repeater to provide communication between the camera and the workstation. The workstation combines the timing information from the binocular camera unit with the camera's intrinsic and extrinsic parameters to achieve 3D measurement of the moving target. This ultimately enables the measurement of the moving target's position, trajectory, velocity, acceleration, and other parameters. As a preferred embodiment, this module matches each data point with a timestamp accurate to milliseconds, sending it in the format: timestamp + space + latitude + longitude + altitude. Compared to the existing NMEA0183 protocol, which is only accurate to the second, this positioning is more precise in time, with synchronization accuracy reaching the nanosecond level. This improves the system's time accuracy, providing more precise spatiotemporal data for subsequent flight trajectory analysis.

[0049] Laser illumination unit: The laser illumination unit is communicatively connected to the passive direction-finding station and the binocular camera unit. Guided by the coordinates of these two units, it provides supplementary illumination to the moving target. This unit employs opto-mechatronics technology to achieve long-range continuous monitoring of the moving target within 1 km. Specifically, this unit includes two sets of laser illumination units and two motorized pan-tilt units, with the two sets of laser illumination units mounted on two separate motorized pan-tilt units. In a preferred embodiment, the two motorized pan-tilt units are placed at two locations approximately 600 m apart.

[0050] The laser illumination unit is used to provide supplementary lighting for moving targets. The binocular high-speed camera subsystem needs to complete real-time measurement of a 20m / s moving target within a short time. Therefore, given the very short sensor integration time, high requirements are placed on the illumination of the moving target. Previous research has also found that in outdoor environments, imaging in the normal visible light band is easily affected by lighting conditions; excessively strong or insufficient light prevents measurement. This project considers using a light source to illuminate the moving target. The light source wavelength is selected from the sensor's sensitive band, and a narrowband filter is placed in front of the optical system to improve the system's anti-interference capability and measurement range. Preferably, a pulsed laser is used. As a new type of light source, laser light sources have advantages over other light sources, such as good monochromaticity, strong directionality, and high brightness. Based on the parameters of commercially available laser illumination cameras, a laser wavelength of approximately 800nm ​​is selected.

[0051] Because laser signals are attenuated by the atmosphere during transmission, in order to ensure that the power of the laser signal after long-distance transmission meets the usage requirements, it is necessary to analyze the influencing factors during transmission and calculate the theoretical power of the laser.

[0052] Due to the complexity of atmospheric physical properties, numerous and highly random factors influence the atmospheric transmission characteristics of lasers, making the calculation of atmospheric transmission attenuation quite challenging. While many studies have analyzed and calculated the atmospheric transmission characteristics of lasers, the data is scattered, with varying research perspectives and focuses. Furthermore, while spectral analysis and calculations based on microscopic atmospheric structure offer high accuracy, they are computationally intensive, overly complex, and impractical. In practical applications, we typically base our calculations on actual measurement data, estimating the attenuation coefficient and transmittance using empirical formulas.

[0053] The main variables for calculating laser atmospheric transmission attenuation include visibility VM (km), precipitation / snow intensity J (mm / h), transmission distance R (km), attenuation coefficient μ (λ) (km-1) or α (λ) (dB / km), and transmittance T (λ).

[0054] Visibility is an indicator of meteorological optical range, generally defined as the maximum distance at which the human eye can detect a black moving target against a background of more than 30° during the day (when the apparent contrast of the moving target is 2%). In practical applications, visibility can be estimated using maps, GPS positioning systems, or information systems, and by referring to typical geographical features. Rainfall / snow intensity refers to the amount of rainfall / snowfall (mm) per unit time (h), with approximate correspondences as follows: light rain 0.1~1 mm / h, moderate rain 1~4 mm / h; heavy rain 4~16 mm / h; torrential rain 16~100 mm / h; extremely heavy rain >100 mm / h. In a uniform atmosphere, the relationship between transmittance T(λ), attenuation coefficient μ(λ), and transmission distance R is: T(λ)=PR / P0=exp(-μ(λ)·R); Where P0 is the laser power before attenuation; P R λ is the attenuated laser power; λ is the wavelength; and R is the transmission distance.

[0055] The atmospheric transmission attenuation of lasers near the selected wavelength band is mainly caused by aerosol absorption and scattering. Atmospheric molecular absorption and scattering have a negligible effect on 1.06 μm lasers and can be ignored in the estimation. The laser attenuation coefficient during the experiment can be calculated using the following formula: ; Where VM is the atmospheric visibility at ground level (km); q is a parameter related to VM, which is generally taken as 1.3. When VM is less than 6km, q can be taken as 0.585×VM1 / 3. Substituting the attenuation coefficient formula into the transmittance formula, the relationship between transmission distance, visibility, and atmospheric transmission transmittance can be obtained.

[0056] Based on the trigonometric relationship, the horizontal divergence length L is: ; Where tan is the tangent function.

[0057] Based on the trigonometric relationship, the vertical divergence length D is: ; The divergence area S of the laser after traveling a certain distance is: ; The inductive power limit Pr of the photoelectric conversion module is: ; Where Ps is the intensity of the sensed light and A is the amplification factor of the photoelectric module.

[0058] Based on the preferred laser parameters designed in this embodiment, X=0.3°, Y=0.3°. Substituting these values ​​into the calculation formula yields... ; According to meteorological data, the average daily sunlight intensity on Earth is approximately 0.135 W per square meter, or Ps = 0.135 W / m². The empirical value for the induction factor of the photoelectric module circuit is A = 1.5. Substituting these values ​​into the calculation formula yields: ; The attenuated laser power Pr is calculated to be 20.25 W.

[0059] Based on engineering empirical formulas, calculations can be performed under the average visible atmospheric conditions. ; According to the transmittance formula, we can obtain... ; In this embodiment, the preferred laser transmission distance R is approximately 1 km.

[0060] Substituting the transmission distance R=1km into the theoretical power calculation formula, we obtain a theoretical peak laser power of 30.62W that satisfies a transmission distance of 1km.

[0061] Based on the formula for calculating the relationship between power and illuminance, a spot area with a diameter of 10m and an emitted laser power of 30.62W can achieve an illuminance of 2.7lx at a distance of 1km. Therefore, the minimum illuminance required for the proposed camera sensor is in the range of 0.05-0.1lx. Figure 5 The schematic diagram of the laser illumination range shown indicates that the illuminance of 2.7 lx meets the test requirements of this embodiment.

[0062] Camera Unit: The camera unit is primarily used for clear, full-process tracking of moving targets under the guidance of the turntable, and for transmitting video data to the industrial control computer in real time for display. Specifically, this unit includes a telephoto camera, which is mounted on one of the motorized pan-tilt units of the laser illumination unit. In a preferred embodiment, a 4-megapixel image sensor is selected to facilitate clear observation of the moving target's flight status.

[0063] Based on the characteristics of moving targets and the number of pixels they occupy on the detector's imaging plane, moving targets can be categorized into point source models and extended sources. Generally, when the angle subtended by the moving target relative to the detector is smaller than its instantaneous field of view, the moving target can be considered a surface source model. In practical applications, moving targets occupying three or more pixels are referred to as extended sources. Through analysis and calculation of the moving target imaging process, the relevant parameters for the photoelectric imaging system's detection and tracking of moving targets can be estimated.

[0064] Based on a network detection accuracy better than 10m, the system's coarse positioning accuracy is obtained as ±5m@1000m. Considering data latency, the tracking response time of conventional equipment is <30ms, and the moving target's flight speed is 20m / s. The 30ms latency corresponds to a flight distance of 0.6m, therefore the telephoto camera's field of view needs to cover 10.6m. Considering the variability of the moving target's flight trajectory, the designed working distance is 800m~1200mm, and the telephoto camera's field of view needs to cover 10.6m. Therefore, the calculated field of view angle fov = -0.852°~1.294°.

[0065] The camera's focal length is related to the target size, the size of the subject, and the working distance. According to the formula: ; Assuming the image sensor is 1 / 1.8" (H=7.178mm, V=5.319mm), we obtain f=574.24-811.99mm. Therefore, the adjustable focal length range of the camera lens to be used needs to cover 550-850mm.

[0066] Workstation Unit: The workstation unit is used to set up, control, post-process data, and display the flight status and trajectory information of moving targets in real time.

[0067] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A real-time optical tracking method for moving targets based on passive guidance, characterized in that, Includes the following steps: S1. Passive Direction Finding Guidance: By using at least two passive direction finding stations to network and cross-locate the radio signals emitted by a moving target, the approximate coordinates of the moving target are obtained. Specifically: ； ； Where D is the straight-line distance between the two passive direction finding stations; The azimuth angle of the passive direction finding station A. The azimuth angle of the passive direction finding station B; S2. Moving target recognition and tracking: Based on approximate coordinates, control the laser illumination unit to rotate toward the moving target and illuminate the approximate coordinate area where the moving target is located; S3. Using the two cameras of the binocular camera unit to acquire image information of the moving target, the acquired image information of the moving target is used to calculate the disparity of the moving target in the images of the two cameras and the system calibration parameters to obtain the three-dimensional coordinates and pose of the moving target in the measurement coordinate system in real time. The specific method for obtaining the three-dimensional coordinates of the moving target in the measurement coordinate system is as follows: obtain the pixel coordinates of the center point of the moving target, and based on the pixel coordinates of the center point of the moving target in the two cameras, calculate the three-dimensional coordinates of the moving target in the measurement coordinate system using the principle of triangulation; the specific method for solving the x-coordinate and y-coordinate of the three-dimensional coordinates of the center point of the moving target is as follows: ； ； in, Let A be the pixel coordinates of the center point of the moving target of camera A. Let the pixel coordinates be the center point of the moving target of camera B. The x and y coordinates of the three-dimensional coordinates of the center point of the moving target; S4. Moving Target Status Monitoring: The portable workstation unit combines multiple sets of position changes of the moving target to determine the trajectory and pose of the moving target; and calls the binocular camera unit to track the moving target throughout the entire process, and transmits the collected flight status of the moving target to the portable workstation unit, thereby realizing real-time monitoring of the moving target's status.

2. The real-time optical tracking method for moving targets based on passive guidance according to claim 1, characterized in that, Step S1 specifically includes: Signal interception and identification: At least two passive direction finding stations are used to capture radio signals emitted by moving targets, and the frequency and modulation characteristics of the radio signals are analyzed to distinguish moving target signals from interference signals; Direction finding calculation: Obtain azimuth data from different passive direction finding stations through network detection, and filter and verify the azimuth data to remove outliers with large errors; Calculation of moving target coordinates: Based on the verified azimuth data and coordinates of the direction finding station, after time synchronization calibration, the approximate coordinates of the moving target are obtained through the cross-positioning algorithm.

3. The real-time optical tracking method for moving targets based on passive guidance according to claim 1, characterized in that, The azimuth angle of passive direction finding station A The azimuth angle of passive direction finding station B The calculation is performed using the following formula: ； ； in, The original azimuth angle of the passive direction finding station A. This is the original azimuth angle of the passive direction finding station B. The static calibration error of passive direction finding station A. This represents the static calibration error of the passive direction finding station B.

4. The real-time optical tracking method for moving targets based on passive guidance according to claim 3, characterized in that, In step S3, the method for determining the pixel coordinates of the moving target center point of cameras A and B is as follows: Set a grayscale threshold T, binarize the difference image, and then calculate the pixel coordinates of the moving target center point. The calculation formula for the pixel coordinates of the moving target center point is: ； in, These are the pixel coordinates of the image. , respectively, are the gray values ​​of the image at (x,y) at time t and time t-1; The grayscale value is the value of the difference image.

5. The real-time optical tracking method for moving targets based on passive guidance according to claim 3, characterized in that, In step S2, controlling the laser illumination unit to rotate toward the moving target specifically involves: reading the calibration coordinates of turntable T1 and turntable T2, obtaining the initial azimuth angles of the two turntables, adding the initial azimuth angles to the real-time angles of the corresponding passive direction finding stations to obtain the rotation control angle, quantizing the rotation control angle into an integer, assembling a data frame in the format of frame header + address code + quantized angle + check bit + frame tail, and sending the data frame to the turntable controller via the RS-422 serial port.

6. A system for the real-time optical tracking method for moving targets based on passive guidance as described in any one of claims 1 to 5, characterized in that, It includes: A passive direction finding station, including an antenna array, a multi-channel receiver, a signal processor, and a portable workstation unit, is used to detect and identify moving target signals. Through multi-station cross-positioning, it monitors the radio spectrum, analyzes the frequency, modulation characteristics, and intensity of characteristic signals, and obtains the approximate coordinates of the moving target. The binocular camera unit includes an image acquisition module, a time synchronization module, an RTK calibration module, and a data transmission module, which are used to acquire image data of moving targets and obtain the three-dimensional coordinates and pose of the moving targets; The laser illumination unit includes a laser illumination unit and a motorized pan-tilt unit. The laser illumination unit is communicatively connected to the passive direction finding station and the binocular camera unit to illuminate the approximate coordinate area where the moving target is located. The camera unit is used to track the moving target throughout its entire journey under the tracking and alignment of the turntable, and transmit video data information to the industrial control computer in real time for display. The portable workstation unit is used for system setup, control, data post-processing, and real-time display of the flight status and trajectory information of moving targets.

7. The system of the real-time optical tracking method for moving targets based on passive guidance according to claim 6, characterized in that, The antenna array of the passive direction finding station is used to intercept the signal of the moving target, and amplify and convert the received signal to an intermediate frequency signal; the multi-channel receiver is used to receive the antenna and channel output signals; the signal processor performs signal detection and parameter estimation on the intermediate frequency signal to obtain the directional characteristic parameters of the moving target, and sends them to the portable workstation unit through the communication transmission network. The portable workstation unit fuses and cross-locates parameters from multiple direction finding stations.

8. The system of the real-time optical tracking method for moving targets based on passive guidance according to claim 6, characterized in that, The image acquisition module of the binocular camera unit includes two sets of cameras and two sets of optical lenses, which can acquire two sets of 2D coordinates of the moving target.

9. The system of the real-time optical tracking method for moving targets based on passive guidance according to claim 6, characterized in that, The timing synchronization module of the binocular camera unit uses B-code timing to achieve synchronization and high-precision time measurement between the two cameras; the RTK calibration module combines the Global Positioning System and differential GPS technology to provide the system with centimeter-level calibration results for moving targets in real time.

10. The system of the real-time optical tracking method for moving targets based on passive guidance according to claim 6, characterized in that, The laser illumination unit includes two sets of laser illumination groups and two motorized pan-tilt units, enabling long-distance continuous monitoring of moving targets within a 1-kilometer range.

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