A dynamic target radial movement identification method and system based on doppler difference imaging

Abstract

This invention discloses a method and system for identifying the radial movement of dynamic targets based on Doppler differential imaging. The method includes: a laser source irradiates a target object and is scattered; the backscattered light signal is received by a receiving system; a beam splitter divides the backscattered light signal into a reference path and a detection path; the reference path signal is received by a reference path array photoelectric detection sensor to obtain the reference path light intensity; a gas cavity is added to the detection path, and the detection path signal is absorbed by the gas cavity and then received by the detection path array photoelectric detection sensor to obtain the detection path light intensity; the pixel positions of the detection path and reference path sensors are aligned; the ratio of the detection path light intensity to the reference path light intensity is calculated; the state of the target object is determined based on whether the calculated value changes; and the target velocity is imaged within the field of view. This invention, by using a gas cavity, can accurately identify the radial velocity of dynamic targets, solving the problem of poor performance of traditional imaging detection techniques for dynamic targets.

Description

Technical Field

[0001] This invention relates to the field of dynamic target imaging and recognition, and in particular to a method and system for identifying the radial movement of dynamic targets based on Doppler differential imaging. Background Technology

[0002] Since the beginning of the 21st century, the number of dynamic targets such as drones and small aircraft in low-altitude open airspace has been increasing. While bringing convenience, this also poses a serious challenge to airspace security and the protection of critical infrastructure. Current imaging and recognition technologies for such targets, whether relying on multi-frame image comparison for motion recognition in traditional optical imaging or on multi-frame point cloud comparison for motion state determination in traditional lidar imaging, all have certain limitations. Due to pixel resolution limitations, small targets moving radially are often difficult to detect observable changes in pixel position, thus making effective recognition impossible solely based on positional offset.

[0003] These methods are susceptible to environmental interference and cannot obtain distance and speed information. They also have poor real-time performance and insufficient sensitivity, making them challenging for applications involving the radial movement of dynamic targets. They are difficult to achieve accurate real-time detection to meet the high reliability requirements for low-altitude security control in scenarios such as airports, borders, and critical facilities. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to address the problem of poor dynamic target recognition performance in current traditional dynamic target imaging and recognition technologies by providing a dynamic target radial movement recognition method and system based on Doppler differential imaging that is highly adaptable to the environment, has a large detection range, high positioning accuracy, and velocity measurement and recognition capabilities.

[0005] Technical solution: The dynamic target radial movement recognition method based on Doppler differential imaging described in this invention includes:

[0006] S1: The laser source is collimated and expanded into the atmosphere by the transmitting telescope. After the laser shines on the target, it is scattered. The backscattered light signal is first filtered by a filter, and then focused and collimated by the convex lens of the imaging system's primary mirror. The beam splitter divides the backscattered light signal into a reference path and a detection path. The reference path signal is directly received by the reference path array photoelectric detection sensor to obtain the reference path light intensity. A gas cavity is added to the detection path. The detection path signal is absorbed by the gas cavity and then received by the detection path array photoelectric detection sensor to obtain the detection path light intensity.

[0007] S2: After the optical signal is converted into an electrical signal, it is received by the computer and the reference path optical intensity and the detection path optical intensity are collected.

[0008] S3: Align the pixel positions of the two sensors based on the pixel information collected by the reference path and the detection path array photoelectric detection sensor.

[0009] S4: Calculate the ratio of the light intensity of the detection path to the light intensity of the reference path. Based on the changes in the calculated value, determine the velocity direction of the target object and perform quantitative imaging of the velocity value.

[0010] Furthermore, in step S1, a gas cavity is added to the detection path to analyze the target information at the pixel position.

[0011] Furthermore, in step S1, different gas chambers are selected, resulting in different gas absorption lines, and different laser emission sources are selected.

[0012] Furthermore, in the gas cavity, when the target is in motion, the detection path signal passing through the gas cavity causes a frequency-dependent intensity change.

[0013] Furthermore, in step S4, a change in the ratio of the light intensity of the detection path to the light intensity of the reference path is determined to be a dynamic target.

[0014] Furthermore, in step S4, if the ratio of the light intensity of the detection path to the light intensity of the reference path does not change, it is determined to be a static target.

[0015] Further, in step S4, the ratio of the light intensity of the detection path to the light intensity of the reference path is calculated to deduce the magnitude and direction of the radial velocity of the target, using the following formula:

[0016]

[0017] Where D represents the probe path, R represents the reference path, t represents time, z represents the pixel position, and C is a constant. Transmittance, The absorption coefficient is... is the optical path length of the gas cavity.

[0018] Furthermore, the aforementioned Absorption coefficient and Doppler frequency shift The relevant formula is as follows:

[0019] .

[0020] Furthermore, based on the ratio of the light intensity of the detection path to the light intensity of the reference path, when the gas transmittance is in a convex enhancement state, it corresponds to a positive Doppler frequency shift; when the gas transmittance is in a concave weakening state, it corresponds to a negative Doppler frequency shift.

[0021] A dynamic target radial motion recognition system based on Doppler differential imaging includes modules:

[0022] The laser emission and echo reception module is used to emit lasers into the atmospheric environment and receive backscattered light signals from the target.

[0023] The optical signal splitting and detection module is used to split the backscattered light signal and convert it into a collectable light intensity signal;

[0024] The signal calibration and data acquisition module is used for preprocessing and integrating the acquired signals;

[0025] The target motion / static discrimination module is used to initially distinguish between dynamic and static targets;

[0026] The motion parameter calculation module is used to calculate the magnitude and direction of the radial velocity of the target;

[0027] The results output module is used to output the final detection results of the target.

[0028] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. Using a gas cavity reduces background and noise interference and improves the accuracy of dynamic target recognition; 2. It can simultaneously measure radial motion speed and direction to achieve target velocity imaging; 3. The internal environment of the gas cavity is stable, the absorption line shape is stable, and the speed measurement and imaging accuracy is high. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the structure of the present invention;

[0030] Figure 2 This is a schematic diagram of the Doppler frequency shift inversion based on the light intensity change of the present invention. In this diagram, (a) represents the transmittance of HF (hydrogen fluoride) gas at a specific wavelength, and (b) represents the schematic diagram of the Doppler frequency shift inversion based on the light intensity change of the absorption line of HF (hydrogen fluoride) at 872 nm.

[0031] Figure 3 This is a flowchart of the present invention;

[0032] Figure 4 Let be a pixel grayscale image, where (a) represents Reference path pixel information when there is no dynamic target at any given time, (b) represents When there is a dynamic target at all times, refer to the path pixel information, (c) represents Detects path pixel information when there are dynamic targets at all times;

[0033] Figure 5 The diagram shows the radial recognition effect of the present invention. In this diagram, (a) represents the transmittance information obtained by combining the light intensity ratio of the detection path and the reference path when the dynamic target is approaching, and (b) represents the transmittance information obtained by combining the light intensity ratio of the detection path and the reference path when the dynamic target is moving away. Detailed Implementation

[0034] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0035] Figure 1This is a structural diagram of the present invention. Figure 3 As shown, the dynamic target radial movement recognition method based on Doppler differential imaging of the present invention includes:

[0036] Laser source 1 and transmitting telescope 2 are set up sequentially along the optical path. Then, laser source 1 and transmitting telescope 2 are connected by optical fiber 11. The Doppler differential imaging laser is turned on, and laser source 1 emits laser light. The laser light is collimated by transmitting telescope 2 and emitted into the atmospheric environment. The laser beam is scattered after irradiating the target object.

[0037] The backscattered light signal is first spectrally filtered by filter 3, and then sequentially focused and collimated by the convex lens 4 and convex lens 5 of the imaging system's primary mirror. The light signal is split into a reference path and a detection path by beam splitter 6. A gas cavity 7 is added to the detection path, which significantly absorbs the detection wavelength. Simultaneously, the gas cavity 7 is located inside the instrument, ensuring stable gas pressure, concentration, and temperature, and a stable absorption line shape.

[0038] The reference path signal is directly received by the reference path array photoelectric detection sensor 9 (including but not limited to CMOS area array sensor, SPAD array, etc.) to obtain the light intensity. The other path serves as the detection light. The signal from the detection path is first absorbed by the gas cavity 7, and then received by the photoelectric detection sensor 8 (including but not limited to CMOS area array sensors, SPAD arrays, etc.) to obtain the light intensity. Simultaneously, the pixel array of the sensor image is acquired. The road surface detection array photoelectric sensor 8 and the reference road surface detection array photoelectric sensor 9 are connected to the computer 10 via cable 12.

[0039] According to the Doppler effect, a moving target will cause a frequency shift in the probe light, resulting in a change in light intensity. The emitted laser frequency is... When the target object approaches (frequency increases) or moves away (frequency decreases), the corresponding frequency will change. or The corresponding light intensity becomes or Calculate the change in light intensity. / or / The gas transmittance also changes with the value. or The Doppler frequency shift is obtained.

[0040] like Figure 2As shown, taking near-infrared lasers around 872 nm as an example, an HF (hydrogen fluoride) gas cavity can be selected, and its characteristic absorption lines in this band can be used to achieve intensity modulation and frequency shift inversion. Based on this principle, the gas transmittance distribution information at the corresponding moment is obtained by calculating the change in light intensity, and then the magnitude and direction of the radial velocity of the detected target are calculated according to the Doppler frequency shift velocimetry formula.

[0041] This scheme can match the characteristic absorption lines of the gas according to the actual detection wavelength. For example, for the 532 nm green light band, the I2 gas absorption line can be selected; for the 589 nm sodium yellow light band, the Na (sodium atom) gas absorption line can be selected; for the mid-infrared band such as 1645 nm, the CH4 (methane) gas absorption line can be selected, and it can also be extended to other gases such as C2H2 (acetylene) and CO (carbon monoxide).

[0042] By selecting a gas absorption line that matches the laser wavelength, the corresponding mapping between light intensity changes and Doppler frequency shifts can be achieved in different wavelength bands. Then, based on the Doppler frequency shift velocimetry formula, the magnitude and direction of the radial velocity of the detected target can be calculated.

[0043] After the optical signal is converted into an electrical signal, it is received by computer 10, and the detection path can be collected at the same time. and reference road Information.

[0044] First, calibrate the pixel information collected by the area array photoelectric detection sensors 8 and 9, and align the pixel positions.

[0045] Through calculation Based on the value of the calculated value, a preliminary judgment can be made as to whether the target is a dynamic or static target.

[0046] The value changes. When the target object moves, the frequency of the received backscattered light signal changes, corresponding to a frequency of... The backscattered light signal obtained from the reference path has an intensity of... After passing through gas cavity 7 on the detection path, the light intensity at the corresponding frequency changes, and the light intensity is... .calculate According to Beer-Lambert's law, the frequency can be calculated from the ratio of light intensities. Magnitude of change:

[0047]

[0048] in Transmittance, The absorption coefficient is... This is the optical path length of gas cavity 7. The absorption coefficient is related to the laser frequency:

[0049]

[0050] Then, based on the Doppler frequency shift formula, the velocity of the target object can be calculated. :

[0051]

[0052] in The wavelength of the emitted light. At the speed of light, The frequency of the emitted light. This is the Doppler frequency shift.

[0053] When the target object moves radially (along the laser emission direction), the light intensity changes. and When the ratio changes, first calculate and The ratio of the values ​​is used to obtain the gas transmittance distribution information at the corresponding time, and then the magnitude and direction of the target's radial velocity are obtained according to the Doppler frequency shift velocimetry formula.

[0054] Meanwhile, as the gas cavity 7 device changes the light intensity, the light signal received by the photoelectric detection sensor 8 on the road surface changes, and the pixel grayscale value of the image on the computer 10 changes, further confirming the dynamic range of the target's radial motion, and finally outputting a clear image of the target and accurate motion speed.

[0055] like Figure 4 As shown, Figure 4 (a) in the text is presented When there are no moving targets, the pixel grayscale distribution image acquired by the reference path contains only static scene information such as background vegetation and buildings, without moving target features, and can be used as the reference background for subsequent differential imaging; however, when there are radially moving targets, such as... Figure 4 As shown in (b) in the figure, The pixel grayscale image acquired by the reference path at any given time is similar to the output of a traditional passive imaging system. It only reflects the grayscale distribution and target location information of the scene at the current moment, and cannot directly obtain the target's motion velocity characteristics; the same At this moment, after the detection path passes through gas cavity 7, the change in light intensity during the radial motion of the target produces a significant effect, such as... Figure 4 As shown in (c), due to the Doppler frequency shift caused by the radial motion of the target, the grayscale response of the dynamic target is significantly different from that of the reference path image after the light signal is absorbed by the gas cavity. This provides a data basis for the subsequent calculation of the light intensity ratio between the detection path and the reference path, and can further realize the differential velocity imaging and accurate identification of the target.

[0056] like Figure 5 As shown, calculate The value of is used to obtain the gas transmittance distribution information at the corresponding time. Combined with the Doppler frequency shift velocimetry formula, the magnitude and direction of the target's radial velocity are inverted. When the target approaches, such as Figure 5 As shown in (a), the light intensity of the detection path signal is significantly enhanced, and the image collected by the corresponding detection path array photoelectric detection sensor 8 exhibits high-brightness spot characteristics.

[0057] Computer 10 calculates Within a single grid cell containing the target, the gas transmittance exhibits a convex enhancement state, corresponding to a positive Doppler frequency shift, which can be used to calculate the target's velocity in the direction of approach; when the target moves away, such as Figure 5 As shown in (b), the intensity of the light intensity of the detection path signal is reduced accordingly, and the image collected by the corresponding detection path array photoelectric detection sensor 8 shows a dark black light spot feature.

[0058] Computer 10 calculates Within a single grid cell containing the target, the gas transmittance exhibits a concave, weakened state, corresponding to a negative Doppler frequency shift. This allows for the calculation of the target's velocity in the direction of departure. By understanding the correspondence between these transmittance distribution characteristics and the Doppler frequency shift, the target's direction of motion can be intuitively distinguished, and its velocity magnitude and dynamic range can be accurately obtained, enabling efficient detection and identification of radially moving targets.

[0059] A dynamic target radial motion recognition system based on Doppler differential imaging, comprising:

[0060] The laser emission and echo reception module is used to emit laser light into the atmosphere and receive the backscattered light signal from the target. This module includes a laser source 1, a transmitting telescope 2, a filter 3, an imaging system primary mirror convex lens 4, and a convex lens 5. The laser emitted from the laser source 1 is emitted into the atmosphere via the transmitting telescope 2. The backscattered light signal generated after the laser is scattered by the target is first filtered by the filter 3, and then focused and collimated sequentially by the imaging system primary mirror convex lens 4 and convex lens 5.

[0061] The optical signal splitting and detection module is used to split the backscattered light signal and convert it into a collectable light intensity signal. This module includes a beam splitter 6, a gas cavity 7, a surface detection array photoelectric sensor 8, and a reference surface array photoelectric sensor 9. The backscattered light signal is split into two paths by the beam splitter 6; one path serves as the reference light, which is directly received by the reference surface array photoelectric sensor 9. The other path serves as the detection light, which, after being absorbed by the gas cavity 7, is received by the photoelectric sensor 8 on the detection surface to obtain the light intensity. .

[0062] The signal calibration and data acquisition module is used for preprocessing and integrating the acquired signals. This module includes a computer 10 and a signal calibration unit. After the optical signal is converted into an electrical signal, it is received and acquired by the computer 10 at different times. and The pixel information collected by the detection road surface array photoelectric detection sensor 8 and the reference road surface array photoelectric detection sensor 9 is calibrated to complete the pixel alignment.

[0063] The target motion / static discrimination module is used to initially distinguish between dynamic and static targets. This module includes a pixel information comparison unit and a light intensity ratio calculation unit. The value determines whether the target is dynamic or static.

[0064] The motion parameter calculation module is used to calculate the radial velocity and direction of the target. When and When the ratio changes, it is calculated The value of is used to obtain the gas transmittance distribution information at the corresponding time, and the radial velocity is obtained by combining the Doppler frequency shift velocimetry formula.

[0065] The results output module outputs the final detection results for the target. This module includes an image generation unit and a motion parameter integration unit. It integrates all data to output a clear image of the target and simultaneously outputs accurate radial velocity magnitude and direction information.

Claims

1. A method for identifying the radial movement of a dynamic target based on Doppler differential imaging, characterized in that, include: S1: The laser source is collimated and expanded into the atmosphere by the transmitting telescope. After the laser shines on the target, it is scattered. The backscattered light signal is first filtered by the filter, and then focused and collimated by the convex lens of the imaging system's main mirror. The beam splitter divides the backscattered light signal into a reference path and a detection path. The reference path signal is directly received by the reference path array photoelectric detection sensor to obtain the reference path light intensity. A gas cavity is added to the detection path. After the detection path signal is absorbed by the gas cavity, it is received by the detection path array photoelectric detection sensor to obtain the detection path light intensity. S2: After the optical signal is converted into an electrical signal, it is received by the computer and the reference path optical intensity and the detection path optical intensity are collected. S3: Align the pixel positions of the two sensors based on the pixel information collected by the reference path and the detection path array photoelectric detection sensor. S4: Calculate the ratio of the light intensity of the detection path to the light intensity of the reference path. Based on the changes in the calculated value, determine the velocity direction of the target object and perform quantitative imaging of the velocity value.

2. The dynamic target radial movement recognition method according to claim 1, characterized in that, In step S1, a gas cavity is added to the detection path to analyze the target information at the pixel position.

3. The dynamic target radial movement recognition method according to claim 1, characterized in that, In step S1, different gas chambers result in different gas absorption lines, and different laser emission sources are selected.

4. The dynamic target radial movement recognition method according to claim 2, characterized in that, When the target is in motion, the detection signal passing through the gas cavity causes a frequency-dependent intensity change.

5. The dynamic target radial movement recognition method according to claim 1, characterized in that, In step S4, a change in the ratio of the light intensity of the detection path to the light intensity of the reference path is determined to be a dynamic target.

6. The dynamic target radial movement recognition method according to claim 1, characterized in that, In step S4, if the ratio of the light intensity of the detection path to the light intensity of the reference path does not change, it is determined to be a static target.

7. The dynamic target radial movement recognition method according to claim 1, characterized in that, In step S4, the ratio of the light intensity of the detection path to the light intensity of the reference path is calculated to deduce the magnitude and direction of the radial velocity of the target, using the following formula: Where D represents the probe path, R represents the reference path, t represents time, z represents the pixel position, and C is a constant. Transmittance, The absorption coefficient is... is the optical path length of the gas cavity.

8. The dynamic target radial movement recognition method according to claim 7, characterized in that, The Absorption coefficient and Doppler frequency shift The relevant formula is as follows: 。 9. The dynamic target radial movement recognition method according to claim 1, characterized in that, Based on the ratio of the light intensity of the detection path to the light intensity of the reference path, when the gas transmittance is in a convex enhancement state, it corresponds to a positive Doppler frequency shift; when the gas transmittance is in a concave weakening state, it corresponds to a negative Doppler frequency shift.

10. A dynamic target radial movement recognition system based on Doppler differential imaging, characterized in that, Includes modules: The laser emission and echo reception module is used to emit lasers into the atmospheric environment and receive backscattered light signals from the target. The optical signal splitting and detection module is used to split the backscattered light signal and convert it into a collectable light intensity signal; The signal calibration and data acquisition module is used for preprocessing and integrating the acquired signals; The target motion / static discrimination module is used to initially distinguish between dynamic and static targets; The motion parameter calculation module is used to calculate the magnitude and direction of the radial velocity of the target; The results output module is used to output the final detection results of the target.

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