CN110806586B - Non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and device - Google Patents

Non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and device Download PDF

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CN110806586B
CN110806586B CN202010016103.2A CN202010016103A CN110806586B CN 110806586 B CN110806586 B CN 110806586B CN 202010016103 A CN202010016103 A CN 202010016103A CN 110806586 B CN110806586 B CN 110806586B
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职亚楠
孙建锋
潘卫清
戴恩文
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Sun Jianfeng
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Hangzhou Ilidar Technology Co ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/06—Systems determining position data of a target
    • G01S17/08—Systems determining position data of a target for measuring distance only
    • G01S17/32—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/88—Lidar systems specially adapted for specific applications
    • G01S17/89—Lidar systems specially adapted for specific applications for mapping or imaging

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Abstract

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.

Description

Non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method and device
Technical Field
The invention relates to the technical field of laser radars, in particular to a laser three-dimensional imaging method and device for speed and distance measurement of non-scanning linear frequency modulation 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 to receive, 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:
Figure GDA0002392333600000041
wherein t is time, E0Is the amplitude, T is the frequency modulation period, f0In order to frequency-modulate the initial frequency,
Figure GDA0002392333600000042
for the frequency modulation rate, B is the bandwidth of the modulation band, phiup(n) is the initial phase of the rising segment of the nth transmitted laser frequency modulation pulse, phidown(n) is the initial phase of the descending segment of the nth transmitted laser frequency modulation pulse;
is split by a 1X 2 beam splitter to obtain a small partEnergy as local oscillator beam with time delay tauLThe optical field is represented as:
Figure GDA0002392333600000051
wherein E isLIs the local oscillator beam amplitude, phiLOIs the noise phase 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 the nth scattering target T on the target planenTime delay τ ofS-nThe linear frequency modulated signal of (a);
in the coordinate system (x, y, z) of the radar-target, TnHas the coordinates of (x)n，yn，zn)，
The radar and the target TnDistance S betweennExpressed as:
Figure GDA0002392333600000052
for long range detection, xn＜＜zn，yn＜＜znThus sn≈zn；
Target TnTime delay tau of an echo beamS-nExpressed as:
Figure GDA0002392333600000053
where c is the speed of light and V is the radar platform and target TnRadial velocity of relative movement, fDopplerIs radar platform and target TnThe doppler shift caused by the radial velocity of the relative motion,
by the resulting time delay τS-nOn the target plane, the nth scattering target TnThe light field of the echo light beam of (a) is expressed as:
Figure GDA0002392333600000061
wherein E isS_nIs the amplitude of the echo beam, phiS-nIs the noise phase of the echo beam.
In the non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method, the nth scattering target T on the target planenThe optical field after the echo light beam and the local oscillator light beam are combined by the 2 × 490 ° spatial optical bridge is expressed as:
Figure GDA0002392333600000062
the four outputs after being mixed by the 2 × 490 ° space optical bridge are respectively:
Figure GDA0002392333600000071
Figure GDA0002392333600000072
wherein phi isN-nIs a mixing noise phase, ISIs a direct current quantity related to the echo beam; i isoIs a direct current quantity related to the local oscillator beam, ηnIs the optical heterodyne receiver directivity function;
in-phase signals and orthogonal signals with orthogonal characteristics output by the space optical bridge connector are respectively received by the 2 XMXN unit dual-channel focal plane array balanced detector to obtain a target T containing M XN points of a target planenIntermediate 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:
Figure GDA0002392333600000073
Figure GDA0002392333600000081
wherein k isinIs a photoelectric detection unit D for receiving in-phase signal channel in a dual-channel focal plane array balanced detectorn-Response rate of (k)quIs a photoelectric detection unit D for receiving orthogonal signal channels in a dual-channel focal plane array balanced detectorn+Response rate of (phi)i-nAnd phiq-nNoise phases of the in-phase signal and the quadrature signal, respectively;
the amplitudes of the in-phase signal and the quadrature signal are simplified:
Figure GDA0002392333600000082
the inphase signal and the orthogonal signal output by the dual-channel focal plane array balanced detector are simplified as follows:
Figure GDA0002392333600000083
Figure GDA0002392333600000084
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:
Figure GDA0002392333600000091
the orthogonal signal path fourier transform is represented as:
Figure GDA0002392333600000092
performing cross-spectrum processing on the two channels:
Figure GDA0002392333600000101
finally, only the imaginary part is taken to obtain
Img＝δ2(f-fn)-δ2(f+fn)，
Extracting the peak position and the positive and negative of the frequency spectrum by a gravity center method to respectively obtain frequency values f in positive frequency modulation and negative frequency modulation processesn：
Figure GDA0002392333600000102
From the above formula, one can obtain:
Figure GDA0002392333600000103
in the above formula, fn-upIs the frequency value in the forward frequency modulation process, fn-downIs the frequency value in the negative frequency modulation process; because the Doppler frequency shift is in direct proportion to the radial speed of the relative motion of the radar platform and the target, the positive and negative Doppler frequency shifts are related to the direction of the radial speed of the relative motion of the radar platform and the target, the positive frequency shift represents that the radar platform and the target move in the opposite direction, and the negative frequency shift represents that the radar platform and the target move in the opposite direction;
therefore, the radar platform and the target T can be obtained by Doppler frequency shiftnThe magnitude and direction of the radial velocity of the relative motion are expressed as
Figure GDA0002392333600000111
Where λ is the output beam wavelength;
obtaining the nth scattering target T on the target plane by the above formulanS distance ofn：
Figure GDA0002392333600000112
In the non-scanning linear frequency modulation continuous wave speed and distance measuring laser three-dimensional imaging method, the nth scattering target T on the target planenThe deflection angle of the echo beam is thetaS-nThen optical heterodyne receives the directional function ηnComprises the following steps:
Figure GDA0002392333600000113
wherein, J1Is a first order Bessel function, K is the magnification of the optical telescope, D0Is the diameter of the photodetecting unit, so the reception field angle is expressed as:
Figure GDA0002392333600000114
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:
Figure GDA0002392333600000115
wherein c is the speed of light and B is the linear bandwidth;
the velocity resolution is expressed as:
Figure GDA0002392333600000121
wherein T is the frequency modulation period, f0For frequency-modulated initial frequency, λ0F is the frequency modulation initial wavelength and F is the frequency modulation rate.
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 × 490 ° spatial optical bridge according to 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.
Example (b): the device of the laser three-dimensional imaging method for speed measurement and distance measurement of the scanless linear frequency modulation continuous wave comprises a linear frequency modulation continuous laser light source 1, wherein the laser light source 1 adopts a 1550nm single-mode narrow-line-width continuous optical fiber laser which is safe for human eyes, the line width of the laser is 10kHz, the output power is 20mW, the output of an optical fiber is provided with isolation protection, a frequency modulation signal generated by a frequency modulation signal generator and a fundamental frequency signal generated by a fundamental frequency signal generator are mixed to obtain a mixing signal, the mixing signal is used as a driving signal of an optical fiber phase modulator to drive the optical fiber phase modulator to generate a frequency modulation laser signal, harmonic waves are inhibited through an optical filter, the frequency modulation laser signal of a required order is reserved, the frequency modulation bandwidth is 5GHz, the frequency modulation rate is 5THz/s, symmetrical triangular wave linear modulation is adopted, the frequency of the modulation signal changes in a symmetrical, the first half part is positive frequency modulation, the second half part is negative frequency modulation, fig. 2 shows a symmetrical triangular linear modulation waveform schematic diagram, and the laser light field emission is represented as:
Figure GDA0002392333600000151
wherein t is time, E0Is the amplitude, T is the frequency modulation period, f0In order to frequency-modulate the initial frequency,
Figure GDA0002392333600000152
for the frequency modulation rate, B is the bandwidth of the modulation band, phiup(n) is the nth transmitted laser frequency modulation pulseInitial phase of the rising section, phidown(n) is the initial phase of the descending segment of the nth transmitted laser frequency modulation pulse;
the output laser firstly passes through an online polarizing/controller, the polarization extinction ratio is ensured to be larger than 25dB, and the polarization direction can be controlled to rotate; then the polarized light passes through a 1 × 2 fiber polarization beam splitter 2, and the polarization states of the outgoing two paths of light are horizontal polarization and vertical polarization respectively. The emergent polarization direction is changed by adjusting the online polarizing/controller, so that the light intensity of two paths output by the 1 multiplied by 2 optical fiber polarization beam splitter is ensured to be 1: 99. According to the invention, a horizontal polarized light branch is used as a signal light beam, and a vertical polarized light branch is used as a local oscillator light beam;
local oscillation light beam is time delay tauLThe optical field is represented as:
Figure GDA0002392333600000161
wherein E isLIs the local oscillator beam amplitude, phiLOIs the noise phase of the local oscillator beam;
the signal beam is firstly amplified by an erbium-doped fiber amplifier, the transmitting power is 5W, the signal beam enters a space optical circulator 4 through an optical fiber collimation transmitter, the optical circulator 4 consists of a polarization beam splitter prism, a Faraday optical rotator and a half-wave plate, the Faraday optical rotator rotates the polarization state of horizontal polarized light by 45 degrees, the slow axis of the half-wave plate and the incident polarization state form 22.5 degrees, the polarization state of the transmitted light can be rotated by 90 degrees, and the polarization state of the received light is kept unchanged. The horizontally polarized emitted light passes through a faraday rotator and a half-wave plate, and the polarization state is changed into vertical polarization. Then the light is transmitted out through a transmitting/receiving optical telescope 5 with the power of 10 times to irradiate the target. The target echo beam received by the transmitting/receiving optical telescope 5 is the nth scattering target T on the target planenTime delay τ ofS-nThe linear frequency modulated signal of (a);
in the coordinate system (x, y, z) of the radar-target, T is shown in FIG. 3nHas the coordinates of (x)n，yn，zn)，
The distance S between the radar and the targetnExpressed as:
Figure GDA0002392333600000171
for long range detection, xn＜＜zn，xn＜＜znThus sn≈zn；
Target TnTime delay tau of an echo beamS-nExpressed as:
Figure GDA0002392333600000172
where c is the speed of light and V is the radar platform and target TnRadial velocity of relative movement, fDopplerIs radar platform and target TnThe doppler shift caused by the radial velocity of the relative motion,
by the resulting time delay τS-nOn the target plane, the nth scattering target TnThe light field of the echo light beam of (a) is expressed as:
Figure GDA0002392333600000173
wherein E isS_nIs the amplitude of the echo beam, phiS-nIs the noise phase of the echo beam.
The nth scattering target T on the target planenThe optical field after the echo light beam and the local oscillator light beam are combined by the 2 × 490 ° space optical bridge 6 is expressed as:
Figure GDA0002392333600000181
the spatial optical bridge structure is shown in fig. 4, a free space structure 2 × 490 ° optical bridge is adopted, the clear aperture of the 2 × 490 ° optical bridge is 32mm × 32mm, and the spatial optical bridge structure is composed of a polarization beam splitter prism 171, a total reflection mirror 172, a first half-wave plate 173, a second half-wave plate 174, a third half-wave plate 175, a quarter-wave plate 176, a first polarization beam splitter prism 177, and a second polarization beam splitter prism 178, an echo beam and a local oscillator beam are orthogonally coherently received by the 2 × 490 ° spatial optical bridge, and four outputs after frequency mixing by the 2 × 490 ° spatial optical bridge are respectively:
Figure GDA0002392333600000182
Figure GDA0002392333600000191
wherein phi isN-nIs a mixing noise phase, ISIs a direct current quantity related to the echo beam; i isoIs a direct current quantity related to the local oscillator beam, ηnIs the optical heterodyne receiver directivity function;
thus, from the nth scattering target T on the target planenThe signals are divided into in-phase signals and orthogonal signals with orthogonal characteristics, as shown in fig. 5, the in-phase signals and the orthogonal signals with orthogonal characteristics output by the space optical bridge are respectively processed by D in a 2 × M × N unit dual-channel focal plane array balanced detector 7n-And Dn+Receiving to obtain a target T containing M multiplied by N points of a target planenIntermediate frequency signals of distance and velocity information; the total number of pixels of the 2 XMXN unit dual-channel focal plane array balanced detector is 2X 256, the number of pixels of each channel is 256X 256, each pixel is an InGaAs device, the size of each pixel is 0.1mm, the interval is 0.125mm, the duty ratio is 0.8, the size of each channel photosurface is 32mm X32 mm, two photodiodes with completely similar characteristics are adopted at corresponding positions of the two channel photosurfaces for photoelectric conversion, a differential amplifier is used at the rear end, differential signals are amplified after the two channels are differentiated, and common-mode noise is inhibited; the intermediate frequency signal is an in-phase signal and an orthogonal signal output by the 2 × mxn unit dual-channel focal plane array balanced detector 7, and the signals are respectively:
Figure GDA0002392333600000201
Figure GDA0002392333600000202
wherein k isinIs a photoelectric detection unit D for receiving in-phase signal channel in a dual-channel focal plane array balanced detectorn-Response rate of (k)quIs a photoelectric detection unit D for receiving orthogonal signal channels in a dual-channel focal plane array balanced detectorn+Response rate of (phi)i-nAnd phiq-nNoise phases of the in-phase signal and the quadrature signal, respectively;
simplifying the amplitude of the in-phase and quadrature signals (i.e. reducing the amplitude of the quadrature signal
Figure GDA0002392333600000203
Figure GDA0002392333600000204
Are each independently of the othern-iAnd In-qInstead):
Figure GDA0002392333600000205
then the in-phase signal and the quadrature signal output by the dual-channel focal plane array balanced detector 7 are simplified as follows:
Figure GDA0002392333600000211
Figure GDA0002392333600000212
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:
firstly, fast fourier transform is respectively performed on two channels of data, and the in-phase signal channel fourier transform is expressed as:
Figure GDA0002392333600000213
the orthogonal signal path fourier transform is represented as:
Figure GDA0002392333600000221
performing cross-spectrum processing on the two channels:
Figure GDA0002392333600000222
finally, only the imaginary part is taken to obtain
Img＝δ2(f-fn)-δ2(f+fn)，
Extracting the peak position and the positive and negative of the frequency spectrum by a gravity center method to respectively obtain frequency values f in positive frequency modulation and negative frequency modulation processesn：
Figure GDA0002392333600000223
From the above formula, one can obtain:
Figure GDA0002392333600000231
wherein f isn-upIs the frequency value in the forward frequency modulation process, fn-downThe frequency value in the negative frequency modulation process; because the Doppler frequency shift is in direct proportion to the relative movement speed of the radar platform and the target, the positive and negative Doppler frequency shifts are related to the direction of the radial speed of the relative movement, the positive frequency shift represents that the radar platform and the target move in the opposite direction, and the negative frequency shift represents that the radar platform and the target move in the opposite direction;
therefore, the radar platform and the target T can be obtained by Doppler frequency shiftnThe magnitude and direction of the radial velocity of the relative motion are expressed as
Figure GDA0002392333600000232
Where λ is the output beam wavelength;
obtaining the nth scattering target T on the target plane by the above formulanS distance ofn：
Figure GDA0002392333600000233
The nth scattering target T on the target planenThe deflection angle of the echo beam is thetaS-nThen optical heterodyne receives the directional function ηnComprises the following steps:
Figure GDA0002392333600000234
wherein, J1Is a first order Bessel function, K is the magnification of the optical telescope, D0Is the diameter of the photodetecting unit, so the reception field angle is expressed as:
Figure GDA0002392333600000241
m multiplied by N is the number of pixels of a single channel of the dual-channel focal plane array balanced detector; m is 256 and N is 256;
the reception field angle in this embodiment is 55.5 ° × 55.5 °;
the range resolution is expressed as:
Figure GDA0002392333600000242
wherein c is the speed of light and B is the linear bandwidth;
the distance resolution in this example is 3 cm;
the velocity resolution is expressed as:
Figure GDA0002392333600000243
wherein T is the frequency modulation period, f0For adjustingFrequency initial frequency, λ0F is the frequency modulation initial wavelength and F is the frequency modulation rate.
The velocity resolution in this example is 0.775 mm/s.
After parallel synchronous measurement of the target distance and speed, a distance-intensity three-dimensional point cloud image and a distance-speed three-dimensional point cloud image are respectively constructed by combining an image processor, on one hand, the image processor acquires the detection intensity of each target sampling point by utilizing coherent detection through a pre-designed sampling range and sampling interval of a detected target, on the other hand, the gray information of the detected target is reversely deduced through the relation between the intensity and the target detection, and meanwhile, the round-trip flight time of laser frequency modulation pulses at the sampling points and the two-dimensional space position corresponding to a detection pixel are measured, and the three-dimensional distance image of the target point is obtained; reconstructing a distance-intensity three-dimensional point cloud image of the target by the gray level image and the distance image of the target point, wherein different point cloud colors represent different distances and are displayed by an image display; on the other hand, the speed and the direction of each target sampling point are obtained through the coherent detection, the distance image of the target point is combined, the distance-speed three-dimensional point cloud image of the target is reconstructed, the color of the point cloud only adopts red and blue, the red represents that the radar platform moves opposite to the target, the blue represents that the radar platform moves back to the target, and the depth of the color represents the speed, and the speed is displayed through an image display. Fig. 6 shows a distance-intensity three-dimensional point cloud image and a distance-velocity three-dimensional point cloud image of a moving body measured at a distance of 20 meters in this embodiment, and it can be seen from fig. 6 that the three-dimensional imaging image of the present invention has the characteristics of high resolution and high precision, and the dynamic target image has no distortion. The invention can not only obtain the distance-intensity image containing the gray scale 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, undistorted three-dimensional imaging of the dynamic target and the like.

Claims (9)

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:
Figure FDA0002392333590000021
wherein t is time, E0Is the amplitude, T is the frequency modulation period, f0In order to frequency-modulate the initial frequency,
Figure FDA0002392333590000022
for the frequency modulation rate, B is the bandwidth of the modulation band, phiup(n) is the initial phase of the rising segment of the nth transmitted laser frequency modulation pulse, phidown(n) is the initial phase of the descending segment of the nth transmitted laser frequency modulation pulse;
split by a 1X 2 beam splitter, a small part of energy is used as a local oscillation light beam which is time delay tauLThe optical field is represented as:
Figure FDA0002392333590000023
wherein E isLIs the local oscillator beam amplitude, phiLOIs the noise phase 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 the nth scattering target T on the target planenTime delay τ ofS-nThe linear frequency modulated signal of (a);
in the coordinate system (x, y, z) of the radar-target, TnHas the coordinates of (x)n，yn，zn)，
The radar and the target TnDistance S betweennExpressed as:
Figure FDA0002392333590000031
for long range detection, xn＜＜zn，yn＜＜znThus sn ≈ zn；
Target TnTime delay of echo light beamτS-nExpressed as:
Figure FDA0002392333590000032
where C is the speed of light and V is the radar platform and target TnRadial velocity of relative movement, fDopplerIs radar platform and target TnThe doppler shift caused by the radial velocity of the relative motion,
by the resulting time delay τS-nOn the target plane, the nth scattering target TnThe light field of the echo light beam of (a) is expressed as:
Figure FDA0002392333590000033
wherein E isS_nIs the amplitude of the echo beam, phiS-nIs the noise phase of the echo beam.
4. The laser three-dimensional imaging method for speed and distance measurement of the scanless chirp continuous wave according to claim 3, wherein: the nth scattering target T on the target planenThe optical field after the echo light beam and the local oscillator light beam are combined by the 2 × 490 ° spatial optical bridge is expressed as:
Figure FDA0002392333590000041
the four outputs after being mixed by the 2 × 490 ° space optical bridge are respectively:
Figure FDA0002392333590000042
Figure FDA0002392333590000043
wherein phi isN-nIs a mixing noise phase, IsIs a direct current quantity related to the echo beam; i isoIs a direct current quantity related to the local oscillator beam, ηnIs the optical heterodyne receiver directivity function;
in-phase signals and orthogonal signals with orthogonal characteristics output by the space optical bridge connector are respectively received by the 2 XMXN unit dual-channel focal plane array balanced detector to obtain a target T containing M XN points of a target planenIntermediate 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:
Figure FDA0002392333590000051
Figure FDA0002392333590000052
wherein k isinIs a photoelectric detection unit D for receiving in-phase signal channel in a dual-channel focal plane array balanced detectorn-Response rate of (k)quIs a photoelectric detection unit D for receiving orthogonal signal channels in a dual-channel focal plane array balanced detectorn+Response rate of (phi)i-nAnd phiq-nNoise phases of the in-phase signal and the quadrature signal, respectively;
the amplitudes of the in-phase signal and the quadrature signal are simplified:
Figure FDA0002392333590000053
the inphase signal and the orthogonal signal output by the double-channel focal plane array balanced detector are simplified as follows:
Figure FDA0002392333590000061
Figure FDA0002392333590000062
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:
Figure FDA0002392333590000063
the orthogonal signal path fourier transform is represented as:
Figure FDA0002392333590000071
performing cross-spectrum processing on the two channels:
Figure FDA0002392333590000072
finally, only the imaginary part is taken to obtain
Img＝δ2(f-fn)-δ2(f+fn)，
Extracting the peak position and the positive and negative of the frequency spectrum by a gravity center method to respectively obtain frequency values f in positive frequency modulation and negative frequency modulation processesn：
Figure FDA0002392333590000073
From the above formula, one can obtain:
Figure FDA0002392333590000081
in the above formula, fn-upIs the frequency value in the forward frequency modulation process, fn-downIs the frequency value in the course of negative frequency modulation(ii) a Because the Doppler frequency shift is in direct proportion to the radial speed of the relative motion of the radar platform and the target, the positive and negative Doppler frequency shifts are related to the direction of the radial speed of the relative motion of the radar platform and the target, the positive frequency shift represents that the radar platform and the target move in the opposite direction, and the negative frequency shift represents that the radar platform and the target move in the opposite direction;
therefore, the Doppler frequency shift is used for obtaining the radar platform and the target TnThe magnitude and direction of the radial velocity of the relative motion are expressed as
Figure FDA0002392333590000082
Where λ is the output beam wavelength;
obtaining the nth scattering target T on the target plane by the above formulanS distance ofn：
Figure FDA0002392333590000083
5. The scanless chirp continuous wave velocimetry (FMCW) laser three-dimensional imaging method according to claim 4, wherein:
the nth scattering target T on the target planenThe deflection angle of the echo beam is thetaS-nThen optical heterodyne receives the directional function ηnComprises the following steps:
Figure FDA0002392333590000091
wherein, J1Is a first order Bessel function, K is the magnification of the optical telescope, D0Is the diameter of the photodetecting unit, so the reception field angle is expressed as:
Figure FDA0002392333590000092
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:
Figure FDA0002392333590000093
wherein c is the speed of light and B is the linear bandwidth;
the velocity resolution is expressed as:
Figure FDA0002392333590000094
wherein T is the frequency modulation period, f0For frequency-modulated initial frequency, λ0F is the frequency modulation initial wavelength and F is the frequency modulation rate.
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).
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