Non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and device
阅读说明：本技术 无扫描线性调频连续波测速测距激光三维成像方法及装置 (Non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and device ) 是由 职亚楠 孙建锋 潘卫清 戴恩文 于 2020-01-08 设计创作，主要内容包括：本发明公开了一种无扫描线性调频连续波测速测距激光三维成像方法及装置,雷达平台的线性调频连续激光光源产生的输出光束分为本振光束和信号光束；将信号光束发射至目标并接收目标的回波光束,将回波光束和本振光束通过空间光学桥接器进行相干光混频,利用平衡探测器进行并行平衡接收,获得中频信号,然后采用双通道焦平面读出电路读出中频信号,经滤波处理和采样处理得到采样数据,再使用现场可编程门阵列对采样数据进行处理,实现目标距离和速度的并行同步测量,最后结合图像处理器分别构建三维图像。本发明不仅能获得包含远距离目标灰度信息和空间三维几何位置关系的距离-强度像,还能同时获得雷达平台与目标相对运动径向速度的大小和方向。(The invention discloses a non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and a device, wherein an output light beam generated by a linear frequency modulation continuous laser light source of a radar platform is divided into a local oscillator light beam and a signal light beam; the method comprises the steps of transmitting a signal beam to a target and receiving an echo beam of the target, carrying out coherent light mixing on the echo beam and a local oscillator beam through a space optical bridge, carrying out parallel balanced receiving by using a balanced detector to obtain an intermediate frequency signal, reading the intermediate frequency signal by using a dual-channel focal plane readout circuit, carrying out filtering processing and sampling processing to obtain sampling data, processing the sampling data by using a field programmable gate array to realize parallel synchronous measurement of the distance and the speed of the target, and finally combining an image processor to respectively construct a three-dimensional image. The method can obtain the distance-intensity image containing the gray scale information of the remote target and the spatial three-dimensional geometric position relation, and can also obtain the magnitude and the direction of the radial speed of the relative motion of the radar platform and the target.)
1. The laser three-dimensional imaging method for speed and distance measurement of the non-scanning linear frequency modulation continuous wave is characterized by comprising the following steps: an output light beam generated by a linear frequency modulation continuous laser light source of the radar platform is divided into a local oscillator light beam and a signal light beam by a beam splitter; the method comprises the steps of transmitting a signal beam to a target and receiving an echo beam of the target, carrying out coherent light mixing on the echo beam and a local oscillator beam through a space optical bridge, carrying out parallel balanced receiving by using a dual-channel focal plane array balanced detector to obtain an intermediate frequency signal containing target distance and speed information, reading the intermediate frequency signal by using a dual-channel focal plane reading circuit, carrying out filtering processing and sampling processing on the intermediate frequency signal to obtain sampling data, carrying out real-time parallel fast Fourier transform and cross-spectrum processing on the sampling data by using a field programmable gate array to realize parallel synchronous measurement of target distance and speed, and finally combining an image processor to respectively construct a distance-intensity three-dimensional point cloud image and a distance-speed three-dimensional point cloud image.
2. The laser three-dimensional imaging method for speed and distance measurement of the scanless chirp continuous wave according to claim 1, wherein: the synchronous measurement of the target distance and the target speed is realized, specifically, Fourier transformation is respectively carried out on an in-phase signal and an orthogonal signal output by a dual-channel focal plane array balanced detector, then cross-spectrum processing is carried out to obtain a Doppler frequency spectrum, then an imaginary part of the Doppler frequency spectrum is obtained, the position and the positive and negative of a peak value in the Doppler frequency spectrum are extracted by using a gravity center method to obtain Doppler frequency shift generated by relative motion of a radar platform and a target, and then the size and the direction of the radial speed of the relative motion of the radar platform and the target distance are obtained by the Doppler frequency shift.
3. The laser three-dimensional imaging method for speed and distance measurement of the scanless chirp continuous wave according to claim 1, wherein: the output light beam generated by the linear frequency modulation continuous laser light source is continuous coherent laser with linearly modulated frequency, symmetrical triangular wave linear modulation is adopted, the frequency of a modulation signal changes in a symmetrical triangular mode along with time, in a period, the front half part is positive frequency modulation, the rear half part is negative frequency modulation, and the light field is expressed as follows:
wherein the content of the first and second substances,
split by a 1X 2 beam splitter, a small part of energy is used as a local oscillation light beam which is time delay
wherein the content of the first and second substances,
most energy is used as a signal beam, the signal beam is transmitted to a target through a space optical circulator and an optical telescope, and an echo beam of the target is received by the optical telescope; after passing through the space optical circulator, the echo beam is on the target planeA scattering target
in the radar-target coordinate system
The radar and the target
for the purpose of remote detection of the object,
Target
wherein the content of the first and second substances,
by the resulting time delay
wherein the content of the first and second substances,
4. The laser three-dimensional imaging method for speed and distance measurement of the scanless chirp continuous wave according to claim 3, wherein: on the target plane
，
the four outputs after being mixed by the 2 × 490-degree spatial optical bridge are respectively:
wherein the content of the first and second substances,
in-phase signals and orthogonal signals with orthogonal characteristics output by the space optical bridge are respectively received by the 2 XMXN unit dual-channel focal plane array balanced detector to obtain a target containing M XN points of a target planeIntermediate frequency signals of distance and velocity information; the intermediate frequency signal is an in-phase signal and a quadrature signal output by two channels of the 2 XMXN unit dual-channel focal plane array balanced detector, and the signals are respectively:
wherein
the amplitudes of the in-phase signal and the quadrature signal are simplified:
the inphase signal and the orthogonal signal output by the double-channel focal plane array balanced detector are simplified as follows:
the outputs of the in-phase signal channel and the orthogonal signal channel photoelectric detection units are respectively read out intermediate frequency signals through a dual-channel focal plane readout circuit, and after the intermediate frequency signals are subjected to band-pass filter filtering processing, analog-to-digital conversion is completed through a high-speed analog-to-digital converter, and then the signals are collected by a field programmable gate array, and Doppler frequency shift measurement and distance measurement are respectively performed:
specifically, firstly, the two channels of data are respectively subjected to fast fourier transform, and the in-phase signal channel fourier transform is expressed as:
the orthogonal signal path fourier transform is represented as:
performing cross-spectrum processing on the two channels:
finally, only the imaginary part is taken to obtain
Extracting the peak position and the positive and negative of the frequency spectrum by a gravity center method to respectively obtain frequency values in the positive frequency modulation process and the negative frequency modulation process
From the above formula, one can obtain:
in the above formula, the first and second carbon atoms are,is the frequency value in the forward frequency modulation process,
thus obtaining the radar platform and the target from the Doppler frequency shift
Wherein
obtaining the second on the target plane from the above formula
5. The scanless chirp continuous wave velocimetry (FMCW) laser three-dimensional imaging method according to claim 4, wherein:
on the target plane
，
wherein the content of the first and second substances,
the range resolution is expressed as:
wherein the content of the first and second substances,
the velocity resolution is expressed as:
wherein the content of the first and second substances,
6. The laser three-dimensional imaging method for speed and distance measurement of the scanless chirp continuous wave according to claim 1, wherein: the image processor acquires detection intensity of each target sampling point through preset sampling range and sampling interval of the target by coherent detection, reversely deduces gray information of the target to be detected through the relation between the intensity and the target detection to obtain a gray image of the target point, measures the round-trip flight time of laser frequency modulation pulse at the target sampling point and a two-dimensional space position corresponding to a detection pixel to obtain a three-dimensional distance image of the target point, reconstructs a distance-point cloud intensity three-dimensional point cloud image of the target by the gray image and the three-dimensional distance image of the target point, different colors of point cloud represent different distances, and finally displays the distance image through an image display.
7. The scanless chirp continuous wave velocimetry (FMCW) laser three-dimensional imaging method according to claim 6, wherein: the image processor acquires the speed and the direction of each target sampling point by using coherent detection through a preset sampling range and a preset sampling interval of the target, and reconstructs a distance-speed three-dimensional point cloud image of the target by combining a three-dimensional distance image of the target point.
8. The device for realizing the laser three-dimensional imaging method of speed measurement and distance measurement of the non-scanning linear frequency modulation continuous waves according to any one of claims 1 to 7 is characterized in that: the device comprises a linear frequency modulation continuous laser light source (1), wherein the linear frequency modulation continuous laser light source (1) is connected with a space optical circulator (4) through a beam splitter (2);
the output end of the space optical circulator (4) is connected with an optical telescope (5); the space optical circulator (4) and the beam splitter (2) are connected with a space optical bridge (6) together; the space optical bridge (6) is connected with a double-channel focal plane reading circuit (8) through a double-channel focal plane array balance detector (7), the double-channel focal plane reading circuit (8) is sequentially connected with a band-pass filter (9) and an analog-to-digital converter (10), the analog-to-digital converter (10) is connected with an image processor (12) through a field programmable gate array (11), and the image processor (12) is further connected with an image display (13).
9. The apparatus of claim 8, wherein: and a laser amplifier (3) is also arranged between the beam splitter (2) and the space optical circulator (4).
Technical Field
The invention relates to the technical field of laser radars, in particular to a laser three-dimensional imaging method and device for measuring speed and distance of non-scanning linear frequency-modulated continuous waves。
Background
The laser three-dimensional imaging radar is an active detection technology capable of accurately and quickly acquiring three-dimensional space information of a target, has high imaging space resolution, has strong adaptability to target characteristics and use environment, has unique technical advantages in the aspects of target identification, classification and high-precision three-dimensional imaging and measurement, and is an important means for a maneuvering platform (including vehicle-mounted, airborne, satellite-mounted and the like) to quickly acquire the high-resolution three-dimensional target image information.
The three-dimensional imaging laser radar can be divided into a scanning type and a non-scanning type according to the imaging mode. The scanning type three-dimensional imaging laser radar uses a unit or linear array detector to obtain the height information of each point in a field of view by using two-dimensional point-by-point scanning or one-dimensional line-by-line scanning, and finally performs synthesis processing. The scanning laser imaging radar has the defects of low imaging speed, high laser working frequency, large transmitting power consumption, low imaging resolution and precision, low data splicing precision and the like. When the scanning type laser three-dimensional imaging radar is loaded on a maneuvering platform, the vibration or shake of the platform easily causes data splicing difficulty and seriously affects the measurement precision, so the scanning type laser three-dimensional imaging radar is not suitable for high-precision maneuvering platform three-dimensional imaging application. The scanless laser three-dimensional imaging radar has the advantages of high imaging speed, high frame frequency, high resolution and the like, overcomes the defects of large volume, heavy mass and poor reliability of a scanning type, and plays a vital role in the application of space target relative navigation with higher requirements on real-time performance and volume.
The non-scanning laser three-dimensional imaging radar is divided according to a detection system, and generally adopts two modes of incoherent light direct detection and coherent light heterodyne receiving detection. The incoherent direct detection mode is that pulse laser intensity modulation is adopted at a transmitting terminal, and a photoelectric detection array is adopted at a receiving terminal for direct detection of optical pulses, wherein the common modes mainly include a flash mode based on a linear mode avalanche photodiode (LM-APD) array, a photon counting mode based on a Geiger mode avalanche photodiode (GM-APD) array and a mixing array detection mode based on linear amplitude modulation continuous waves. In the later 90 s of the last century, a Lincoln laboratory of the American Massachusetts institute of technology, Inc. firstly develops a laser three-dimensional imaging radar research based on a GM-APD array under the support of an American DARPA and an air force laboratory, the research and development of GM-APD focal plane array devices with pixel numbers of 4 × 4, 32 × 32, 128 × 32 and 256 × 256 respectively are reported in sequence until 2002, and meanwhile, a plurality of generations of airborne laser three-dimensional imaging radar systems are developed. A frequency mixing array detection laser three-dimensional imaging radar FOPEN based on linear amplitude modulation continuous waves is developed in the United states army laboratory in 2007, a 1550nm continuous output laser diode is adopted, a Direct Digital Synthesizer (DDS) is adopted to achieve intensity modulation, a 640 x 512 pixel array EBAPS detector is adopted as a signal receiving end, the field angle is 35 degrees x 35 degrees, and the distance measurement precision is less than 3 cm. Although the incoherent direct detection mode has high imaging speed, does not need a complex scanning mechanism, and has the capability of flash three-dimensional imaging, the incoherent direct detection mode also requires that the echo power of the laser received by the system is uniformly distributed on each detection pixel, and under the condition of the same laser emission total power and receiving aperture, the more detection pixels are, the smaller the echo power dispersed on each pixel is, so that the detection sensitivity of the area array imaging system is generally lower, and the incoherent direct detection mode is generally only suitable for three-dimensional imaging detection at a short distance. Although single photon detection technology is mature and detection sensitivity is higher, the cost of the device is too high.
The coherent heterodyne detection method adopts local oscillator laser and echo beam laser to perform heterodyne technology on a photoelectric detector, can naturally inhibit background noise and improve the signal-to-noise ratio, and is typically a linear frequency modulation continuous wave coherent laser radar. In 2012, Brian W. Krause adopts a high-speed CCD area array for receiving, and realizes non-scanning linear frequency modulation continuous wave coherent three-dimensional imaging at a distance of 1 meter indoors through motion compensation. However, the application of the coherent detection technology to the non-scanning three-dimensional imaging of the long-distance target has not been reported so far. In addition, all the existing scanning-free laser three-dimensional imaging radars, including a phase discrimination type, a polarization modulation type, a gain modulation type, a fringe tube detector type and the like, cannot realize direct measurement of target speed.
Disclosure of Invention
The invention aims to provide a laser three-dimensional imaging method and device for speed and distance measurement of a non-scanning linear frequency-modulated continuous wave. The invention can not only obtain the distance-intensity image containing the gray information of the remote target and the spatial three-dimensional geometric position relation, but also obtain the size and the direction of the radial speed of the relative motion of the radar platform and the target, and has the advantages of small volume, light weight, high resolution, high precision and undistorted three-dimensional imaging of the dynamic target.
The technical scheme of the invention is as follows: a non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method is characterized in that an output light beam generated by a linear frequency modulation continuous laser light source of a radar platform is divided into a local oscillator light beam and a signal light beam through a beam splitter; the method comprises the steps of transmitting a signal beam to a target and receiving an echo beam of the target, carrying out coherent light mixing on the echo beam and a local oscillator beam through a space optical bridge, carrying out parallel balanced receiving by using a dual-channel focal plane array balanced detector to obtain an intermediate frequency signal containing target distance and speed information, reading the intermediate frequency signal by using a dual-channel focal plane reading circuit, carrying out filtering processing and sampling processing on the intermediate frequency signal to obtain sampling data, carrying out real-time parallel fast Fourier transform and cross-spectrum processing on the sampling data by using a field programmable gate array to realize parallel synchronous measurement of target distance and speed, and finally combining an image processor to respectively construct a distance-intensity three-dimensional point cloud image and a distance-speed three-dimensional point cloud image.
The synchronous measurement of the target distance and speed is realized by the laser three-dimensional imaging method for speed measurement and ranging of the scanless linear frequency modulation continuous wave, specifically, the synchronous measurement of the target distance and speed is realized by respectively carrying out Fourier transform on an in-phase signal and an orthogonal signal output by a dual-channel focal plane array balanced detector, then carrying out cross-spectrum processing to obtain a Doppler frequency spectrum, then taking an imaginary part of the Doppler frequency spectrum, extracting the position and the positive and negative of a peak value in the Doppler frequency spectrum by using a gravity center method to obtain Doppler frequency shift generated by the relative motion of a radar platform and a target, and then obtaining the size and the direction of the radial speed of the relative motion of the.
In the above three-dimensional imaging method using non-scanning chirped continuous wave speed and distance measurement laser, an output light beam generated by the chirped continuous laser light source is a frequency-linearly modulated continuous coherent laser, a symmetric triangular wave is used for linear modulation, the frequency of a modulation signal changes in a symmetric triangular shape with time, in a period, the first half is a positive frequency modulation, the second half is a negative frequency modulation, and the light field is represented as:
wherein the content of the first and second substances,
Split by a
wherein the content of the first and second substances,is the amplitude of the local oscillator beam,
most energy is used as a signal beam, the signal beam is transmitted to a target through a space optical circulator and an optical telescope, and an echo beam of the target is received by the optical telescope; after passing through the space optical circulator, the echo beam is on the target plane
in the radar-target coordinate system
The radar and the target
for the purpose of remote detection of the object,
targetTime delay of echo light beam
wherein the content of the first and second substances,
by the resulting time delayOn the target plane
wherein the content of the first and second substances,
In the above non-scanning linear frequency modulation continuous wave velocity and distance measuring laser three-dimensional imaging method, the first step on the target plane
，
the four outputs after being mixed by the 2 × 490-degree spatial optical bridge are respectively:
wherein the content of the first and second substances,is a mixing of the noise phases and is,
in-phase signals and orthogonal signals with orthogonal characteristics output by the space optical bridge are respectively received by the 2 XMXN unit dual-channel focal plane array balanced detector to obtain a target containing M XN points of a target plane
wherein
the amplitudes of the in-phase signal and the quadrature signal are simplified:
the inphase signal and the orthogonal signal output by the dual-channel focal plane array balanced detector are simplified as follows:
，
the outputs of the in-phase signal channel and the orthogonal signal channel photoelectric detection units are respectively read out intermediate frequency signals through a dual-channel focal plane readout circuit, and after the intermediate frequency signals are subjected to band-pass filter filtering processing, analog-to-digital conversion is completed through a high-speed analog-to-digital converter, and then the signals are collected by a field programmable gate array, and Doppler frequency shift measurement and distance measurement are respectively performed:
specifically, firstly, the two channels of data are respectively subjected to fast fourier transform, and the in-phase signal channel fourier transform is expressed as:
the orthogonal signal path fourier transform is represented as:
performing cross-spectrum processing on the two channels:
finally, only the imaginary part is taken to obtain
Extracting the peak position and the positive and negative of the frequency spectrum by a gravity center method to respectively obtain frequency values in the positive frequency modulation process and the negative frequency modulation process
From the above formula, one can obtain:
in the above formula, the first and second carbon atoms are,
therefore, the radar platform and the target can be obtained by Doppler frequency shift
Wherein
obtaining the second on the target plane from the above formula
In the non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method, the first step is that on a target plane
wherein the content of the first and second substances,
m multiplied by N is the number of pixels of a single channel of the dual-channel focal plane array balanced detector;
the range resolution is expressed as:
，
wherein the content of the first and second substances,
the velocity resolution is expressed as:
wherein the content of the first and second substances,in order to have a frequency-modulated period,is a primary frequency modulationThe frequency of the start-up is,
According to the scanning-free linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method, the image processor acquires the detection intensity of each target sampling point through the preset sampling range and sampling interval of the target by coherent detection, reversely deduces the gray information of the detected target through the relation between the intensity and the target detection to obtain the gray image of the target point, measures the round-trip flight time of laser frequency modulation pulses at the target sampling points and the two-dimensional space position corresponding to the detection pixel to obtain the three-dimensional distance image of the target point, reconstructs the distance-intensity three-dimensional point cloud image of the target through the gray image and the three-dimensional distance image of the target point, and finally displays the distance-intensity three-dimensional point cloud image through the image display.
According to the scanning-free linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method, the image processor acquires the speed and direction of each sampling point of the target by coherent detection through the preset sampling range and sampling interval of the target, and a distance-speed three-dimensional point cloud image of the target is reconstructed by combining the three-dimensional distance image of the target point.
The device for realizing the non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method is characterized in that: the linear frequency modulation continuous laser light source is connected with a space optical circulator through a beam splitter;
the output end of the space optical circulator is connected with an optical telescope; the space optical circulator and the beam splitter are connected with a space optical bridge together; the space optical bridge is connected with a double-channel focal plane reading circuit through a double-channel focal plane array balance detector, the double-channel focal plane reading circuit is sequentially connected with a band-pass filter and an analog-to-digital converter, the analog-to-digital converter is connected with an image processor through a field programmable gate array, and the image processor is further connected with an image display.
In the foregoing apparatus, a laser amplifier is further disposed between the beam splitter and the spatial optical circulator.
Compared with the prior art, the output light beam generated by the linear frequency modulation continuous laser light source is divided into the local oscillation light beam and the signal light beam by the beam splitter; the method comprises the steps of transmitting a signal beam to a target and receiving an echo beam of the target, carrying out coherent light mixing on the echo beam and a local oscillator beam through a space optical bridge, carrying out parallel balanced receiving by using a dual-channel focal plane array balanced detector to obtain an intermediate frequency signal containing target distance and speed information, reading the intermediate frequency signal by using a dual-channel focal plane reading circuit, carrying out filtering processing and sampling processing to obtain sampling data, carrying out real-time parallel fast Fourier transform and cross-spectrum processing on the sampling data by using a field programmable gate array to realize parallel synchronous measurement of the target distance and speed, and respectively constructing a distance-intensity three-dimensional point cloud image and a distance-speed three-dimensional point cloud image by combining with an image processor. Therefore, the method can be used for scanning-free imaging of the remote target by combining the coherent detection technology with the array detection technology, can obtain a distance-intensity image containing the gray scale information of the remote target and the spatial three-dimensional geometric position relation, and can also obtain the size and the direction of the radial speed of the relative motion of the radar platform and the target; in addition, the invention realizes the coaxial receiving and transmitting through the space optical circulator and the optical telescope, is beneficial to the integration miniaturization and reduces the complexity of the system; the invention can achieve the purpose of three-dimensional imaging without a complex scanning mechanism, has the advantages of high resolution, high precision and undistorted imaging on the premise of small volume and simple structure, and has lower cost compared with the existing scanless three-dimensional imaging technology, thereby having good development prospect.
Drawings
Fig. 1 is a schematic structural view of the present invention.
Fig. 2 is a schematic diagram of a symmetrical triangular linear modulation waveform according to the present invention.
Fig. 3 is a schematic diagram of the coordinate system of the radar-target of the present invention.
Fig. 4 is a schematic diagram of a 2 x 490 ° spatial optical bridge of the present invention.
FIG. 5 is a schematic diagram of a dual channel focal plane array balanced detector of the present invention.
FIG. 6 shows the distance-intensity three-dimensional point cloud image and the distance-velocity three-dimensional point cloud image of the moving body measured at a distance of 20 meters in the example.
The labels in the figures are: 1. a linear frequency modulated continuous laser light source; 2. a beam splitter; 3. a laser amplifier; 4. a spatial optical circulator; 5. an optical telescope; 6. a spatial optical bridge; 7. a dual-channel focal plane array balance detector; 8. a dual-channel focal plane readout circuit; 9. a band-pass filter; 10. an analog-to-digital converter; 11. a field programmable gate array; 12. an image processor; 13. an image display; 171. a polarization beam splitter prism; 172. a total reflection mirror; 173. a first half wave plate; 174. a second half-wave plate; 175. a third half-wave plate; 176. a quarter wave plate; 177. a first polarization beam splitting combination prism; 178. and the second polarization beam splitting and combining prism.
Detailed Description
The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.
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