Air target velocity vector remote sensing method

Abstract

The invention discloses an aerial target velocity vector remote sensing method. The method comprises the following steps: transmitting an annular light beam with a linear divergence characteristic through a laser radar system; the receiving system is divided into two paths, one path obtains the distance of a target through a distance measuring detector, and the other path obtains the azimuth angle of the target through an area array sensor; establishing a three-dimensional coordinate system, resolving to obtain a spatial three-dimensional coordinate of the target relative to the laser radar system based on the divergence characteristic, the distance and the azimuth angle of the annular beam, and recording a timestamp; when the target passes through the annular light beam for multiple times, clustering data points based on spatial-temporal characteristics: data continuously collected at the same position belong to the same cluster; and averaging data belonging to the same cluster, and when two clusters of effective data exist and azimuth angles are different, calculating a velocity vector of the target relative to the laser radar system. By utilizing the method, the spatial position and the velocity vector of the target can be quickly and accurately obtained under a simple background.

Description

Technical Field

[0001] The invention belongs to the technical field of laser radar detection, and in particular relates to a remote sensing method for air target velocity vector. Background Art

[0002] As an active remote sensing technology, LiDAR (Light Detection and Ranging) has been widely used in environmental monitoring, target detection, terrain mapping and other fields.

[0003] Conventional LiDAR systems usually use mechanical rotation or galvanometer scanning to scan the laser beam point by point to obtain target information. In recent years, with the development and application of phased array, MEMS and other technologies, the scanning speed and control accuracy of the laser beam have been improved. However, the above methods still have problems such as low scanning efficiency and insufficient dynamic target tracking capabilities. For high-speed moving aerial targets, the above technologies are difficult to quickly and synchronously obtain the three-dimensional position and velocity vector information of the target.

[0004] Although non-scanning LiDAR based on area array sensors can improve detection efficiency, it is limited by the matching problem between the light field divergence characteristics and the target motion model, and the velocity vector solution accuracy is insufficient. In addition, the target positioning accuracy is also limited by the resolution of the area array sensor.

[0005] Chinese patent documents with publication numbers CN118244287A and CN118243960A respectively proposed methods for detecting the velocity vector of annular light targets for atmospheric and ocean scattering media, but they lack effective spatial coordinate solution methods and spatiotemporal clustering algorithms, data aliasing will lead to invalid detection of velocity vectors, and the system has poor robustness.

[0006] The Chinese patent document with publication number CN118778143A proposes using two single-pixel detectors to detect the distance and azimuth of the target respectively, thereby improving the detection frame rate. However, it does not take into account the different intensities of the target reflection signal at different distances, and cannot effectively extract the azimuth of the target. Summary of the invention

[0007] The invention provides an aerial target velocity vector remote sensing method, which can quickly and accurately obtain the spatial position and velocity vector of the target under a simple background.

[0008] A method for remote sensing an aerial target velocity vector comprises the following steps: (1) The laser radar system emits a ring-shaped light beam with a linear divergence characteristic, and the divergence characteristic satisfies ,in For annular beams, the transmission distance The radius at is the divergence constant; (2) The receiving system is split into two paths. One path obtains the distance to the target through a ranging detector , and the other path obtains the azimuth angle of the target through a planar array sensor ; (3) A three-dimensional coordinate system is established. Based on the divergence characteristics of the annular beam , distance and azimuth angle , the three-dimensional spatial coordinates of the target relative to the lidar system are calculated and solved , and the timestamp is recorded ; (4) When the target passes through the annular beam multiple times, clustering based on spatio-temporal features is performed on the data points: the data continuously collected at the same position belongs to the same cluster; (5) The data belonging to the same cluster is averaged. When there are two clusters of valid data with different azimuth angles, according to the spatio-temporal coordinate averages of the two clusters of data and the velocity vector of the target relative to the lidar system is calculated .

[0009] Preferably, in step (1), the annular light field with linear divergence characteristics can be modulated by a spatial light modulator, a phase plate, an axicon, a cylindrical lens, etc., including but not limited to linearly divergent annular lights such as vortex light, perfect vortex light, Bessel-Gaussian light, etc.

[0010] Preferably, in step (1), the working wavelength of the lidar is in the short-wave infrared band of the atmospheric window.

[0011] Preferably, in step (2), the ranging detector is an avalanche photodiode, and the planar array sensor is a CCD or CMOS sensor. The azimuth angle of the target is extracted through image processing.

[0012] Preferably, in step (3), the origin of the three-dimensional coordinate system is the lidar system, and the positive direction of the z-axis is the direction of the optical axis emitted by the lidar system.

[0013] Preferably, in step (3), the three-dimensional spatial coordinates of the target relative to the lidar system are calculated and solved , and the formula is: ; ; .

[0014] Preferably, in step (4), DBSCAN clustering algorithm is used for clustering the data points based on spatio-temporal features, and the clustering radius R is positively correlated with the target size.

[0015] Preferably, after step (5), the following steps are further included: Construct a world coordinate system based on the initial position of the lidar system relative to the ground. When the lidar has a scanning rotation, correct the actual coordinates and velocity of the target according to the scanning angle and angular velocity of the lidar: ; ; .

[0016] Wherein, is the horizontal rotation angle of the lidar system, is the pitch angle of the lidar system, is the horizontal scanning angular velocity of the lidar system, is the pitch scanning angular velocity of the lidar system, is the target space coordinate based on the ground coordinate system, is the actual moving velocity of the target, is the lidar system at a distance of the scanning linear velocity at the place.

[0017] Preferably, the transmitting optical path and the receiving optical path of the lidar system are coaxial, so that the annular beam emitted by the lidar matches the center of the receiving field of view, reducing the detection blind area and simplifying the data processing flow at the same time.

[0018] Preferably, the receiving system uses a beam splitting module to split the echo signal returned after the annular beam irradiates the target to a ranging detector and a planar array sensor. The beam splitting module can use beam splitting components such as beam splitting prisms and beam splitting sheets, and the splitting ratio of the splitting element needs to be selected according to the sensitivities of the detector and the planar array sensor.

[0019] Preferably, a timing control device is used to synchronously trigger the pulsed laser, the ranging detector and the planar array sensor of the lidar; the timing control device has three outputs, and the relative delay of each output is calibrated according to the external trigger delay of the pulsed laser, the ranging detector and the planar array sensor to achieve the synchronization of the timing signals of multiple sensors and facilitate subsequent data fusion.

[0020] Preferably, the planar array sensor has a gating function, and the opening and closing of the gate are controlled by the high and low levels of the signal of the timing control device to realize the functions of delayed exposure and controlled exposure time, thereby suppressing the invalid lidar backscattering signal and improving the signal-to-noise ratio.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The present invention can fully combine the divergence characteristics of the annular beam, combine the azimuth information of the area array sensor and the distance information collected by the detector, calculate the three-dimensional coordinates of the target, quickly and accurately obtain the spatial position of the target, and classify the data based on the clustering algorithm, so as to effectively achieve the accurate detection of the velocity vector. Description of the Drawings

[0022] Figure 1 It is a flowchart of a method for remotely sensing the velocity vector of an aerial target according to an embodiment of the present invention.

[0023] Figure 2 It is a schematic diagram for calculating the three-dimensional coordinates in space of two contacts when the linearly divergent annular light contacts the moving target twice.

[0024] Figure 3 It is a schematic example diagram for clustering data according to spatio-temporal characteristics when the linearly divergent annular light contacts the moving target twice and there are multiple valid data each time.

[0025] Figure 4 It is a schematic diagram of the structure of the lidar system designed to implement the method of the present invention.

[0026] Figure 5 It is the distribution of 8 groups of moving trajectory examples at a set distance of 1000 m.

[0027] Figure 6 It is the comparison result of the set speed value, the calculated speed and the speed components. Detailed Embodiment

[0028] The following further describes the present invention in detail with reference to the drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention, but do not limit it in any way.

[0029] A method for remotely sensing the velocity vector of an aerial target, the specific flowchart is as Figure 1 shown. Based on the divergence characteristics of the annular beam, the distance information and the azimuth angle information, the three-dimensional coordinates of the target in space are calculated, and then the data is clustered according to the spatio-temporal characteristics of the data. When the same target contacts the ring twice, two clusters of data can be obtained, and thus the velocity vector of the target can be calculated.

[0030] As Figure 2 shown, the lidar emits an annular beam with linearly divergent characteristics, where the radius of the annular beam at a distance is . A three-dimensional coordinate system in space is constructed with the lidar as the reference, where the z-axis coincides with the central axis of the annular beam. When the target moves through the annular beam at a certain speed, the spatial coordinates of the target can be obtained. AsFigure 3 As shown, affected by the target size and the thickness of the annular beam, when the target passes through the annular beam, different parts of the target at the same spatial position will be irradiated by the annular beam and form valid data, resulting in multiple sets of data at the same spatial position. Therefore, it is necessary to perform clustering analysis on the data, and the valid data formed at the same spatial position belongs to the same cluster. When the target passes through the annular beam twice, two clusters of data are formed.

[0031] The key components of the lidar system are as Figure 4 shown. The beam emitted by the laser is collimated by a beam expander and then passes through an axicon to generate an annular beam. The receiving system and the transmitting system are designed in a coaxial mode. After the echo signal passes through the telescope, the interference light of other bands is filtered by a filter, and then the echo signal is split into two by a beam splitter and received by a detector and a area array sensor through a focusing lens respectively. The lidar system is also equipped with a timing control device to achieve synchronous triggering of the signals of the laser, the area array sensor and the detector acquisition module. Finally, by processing the signals of the area array sensor and the detector acquisition module by a computer, the azimuth angle information and the distance information of the target can be obtained.

[0032] In this embodiment, according to Figure 5 the set moving trajectories of 8 groups of targets are as follows: (1) moving only in the x-axis direction and passing through the center of the annular beam; (2) moving only in the x-axis direction but not passing through the center of the annular beam; (3) moving only in the y-axis direction and passing through the center of the annular beam; (4) moving only in the y-axis direction but not passing through the center of the annular beam; (5) having the same moving components in the x and y axes and passing through the center of the annular beam; (6) having the same velocity components in the x, y, and z axes; (7) only the velocity component in the x-axis direction is 0; (8) only the velocity component in the y-axis direction is 0. The absolute value of the target velocity is set to 10 m / s, and the distance from the lidar system is 1000 m.

[0033] The remote sensing of the target velocity vector is realized through the following steps: The first step: Obtain the divergence characteristics of the annular beam emitted by the lidar and obtain the radius of the ring at different distances .

[0034] The second step: Through the lidar system as Figure 4 shown, obtain the information of the detector and the area array sensor respectively. Through the timing control generator, delay the opening time of the area array sensor to 100 m and control the closing time at 3000 m to filter the near-field strong backscattering signal. Since the detector and the area array sensor are synchronously triggered by the timing control generator, the timing synchronization of the distance information and the azimuth angle information can be simply realized.

[0035] Step 3: Based on the divergence characteristics of the annular beam , distance , and azimuth angle , the three-dimensional spatial coordinates of the target relative to the lidar system are calculated ; ; ; .

[0036] Among them, , which is obtained in Step 1.

[0037] Step 4: As shown in Figure 3 , when the target passes through the annular beam twice, clustering analysis based on spatio-temporal characteristics is performed on the data points to separate the data points generated during the two contacts.

[0038] Step 5: The valid data points belonging to the same cluster are averaged to calculate the spatio-temporal coordinate average values and , and then the velocity vector of the target is calculated.

[0039] For 8 groups of motion trajectories, the comparison between the calculated velocity vectors and the set values is shown in Figure 6 . The abscissa is the test sample number, and the ordinates in the four subgraphs are the absolute value of the velocity and the magnitudes of the velocity components along the x, y, and z axes respectively. It can be seen that whether it is the absolute value of the velocity or the velocity components of each coordinate axis, the detected values and the set true values are highly consistent, indicating that this method has extremely high stability and accuracy.

[0040] The above embodiments have detailed the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for remotely sensing the velocity vector of an aerial target, characterized in that, Including the following steps: (1) Transmit an annular beam with linear divergence characteristics through a lidar system, and the divergence characteristics satisfy , where is the radius of the annular beam at the transmission distance , and is the divergence constant; (2)The receiving system is split into two paths. One path obtains the distance to the target through a ranging detector , and the other path obtains the azimuth angle of the target through a area array sensor ; (3) Establish a three-dimensional coordinate system, based on the divergence characteristics of the annular beam , distance and azimuth , calculate and obtain the three-dimensional spatial coordinates of the target relative to the lidar system , and record the timestamp ; (4) When the target passes through the annular light beam multiple times, perform clustering of data points based on spatio-temporal features: data continuously collected at the same position belong to the same cluster; (5) Average the data belonging to the same cluster. When there are two clusters of valid data with different azimuth angles, calculate the velocity vector of the target relative to the lidar system according to the spatio-temporal coordinate averages of the two clusters of data and .

2. The remote sensing method for the velocity vector of an airborne target according to claim 1, characterized in that, In step (2), the ranging detector is an avalanche photodiode, the area array sensor is a CCD or CMOS sensor, and the azimuth angle of the target is extracted through image processing.

3. The remote sensing method for the velocity vector of an aerial target according to claim 1, characterized in that, In step (3), the origin of the three-dimensional coordinate system is the lidar system, and the positive direction of the z-axis is the direction of the optical axis emitted by the lidar system.

4. The remote sensing method for the velocity vector of an aerial target according to claim 1, wherein In step (3), the three-dimensional spatial coordinates of the target relative to the lidar system are calculated , and the formula is: ； ； 。 5. The method for remotely sensing the velocity vector of an aerial target according to claim 1, characterized in that In step (4), the DBSCAN clustering algorithm is used to perform clustering of data points based on spatio-temporal features, and the clustering radius R is positively correlated with the target size.

6. The method for remotely sensing the velocity vector of an aerial target according to claim 1, characterized in that After step (5), the following steps are further included: Construct a world coordinate system based on the initial position of the lidar system relative to the ground. When the lidar has a scanning rotation, correct the actual coordinates and speed of the target according to the scanning angle and angular velocity of the lidar: ； ； ； Among them, is the horizontal rotation angle of the lidar system, is the pitch angle of the lidar system, is the horizontal scanning angular velocity of the lidar system, is the pitch scanning angular velocity of the lidar system, is the target space coordinate based on the ground coordinate system, is the actual motion speed of the target, is the lidar system at a distance of the scanning line speed at that point.

7. The method for remotely sensing the velocity vector of an aerial target according to claim 1, characterized in that, The emission optical path and the reception optical path of the lidar system are coaxial, so that the annular light beam emitted by the lidar matches the center of the reception field of view.

8. The method for remotely sensing the velocity vector of an airborne target according to claim 1, characterized in that, The reception system uses a beam splitting module to split the echo signal returned after the annular light beam irradiates the target to the ranging detector and the area array sensor.

9. The remote sensing method for the velocity vector of an airborne target according to claim 1, characterized in that, A timing control device is used to synchronously trigger the pulsed laser, the ranging detector and the area array sensor of the lidar; the timing control device has three outputs, and the relative delay of each output is calibrated according to the external trigger delay of the pulsed laser, the ranging detector and the area array sensor to achieve the synchronization of the timing signals of multiple sensors.

10. The method for remotely sensing the velocity vector of an aerial target according to claim 9, characterized in that, The area array sensor has a gating function, and the opening and closing of the gating are controlled by the high and low levels of the signal of the timing control device, so as to realize the functions of delayed exposure and control of the exposure time, thereby suppressing the invalid lidar backscattering signal and improving the signal-to-noise ratio.

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