阅读说明：本技术 同轴多视场融合线性调频连续波测距测速方法及装置 (Coaxial multi-field-of-view fusion linear frequency modulation continuous wave distance and speed measuring method and device ) 是由 职亚楠 邹瑜 孙建锋 卢智勇 奚庆新 于 2021-08-30 设计创作，主要内容包括：本发明公开了一种同轴多视场融合线性调频连续波测距测速方法及装置,将光信号分为N个通道的光信号,每个通道的光信号先经过移频再分为本振信号和发射信号；将N个通道的发射信号并行发射至目标并接收回波信号,每个通道对应不同距离的视场,每个通道各自的发射/接收视场的完全匹配,实现每个通道视场的中心同轴；回波信号与本振光信号通过相干光混频,采用平衡接收获得中频信号,经滤波和采样后进行实时的并行快速傅里叶变换,实现N个通道距离和速度的同步测量,在上位计算机实现不同距离同轴多视场探测点云数据的融合和输出显示。本发明可以同时扩大激光雷达视场角和提高角分辨率,并能有效克服同轴多视场探测过程中的串扰。(The invention discloses a coaxial multi-field-of-view fusion linear frequency modulation continuous wave distance and speed measurement method and a device, wherein an optical signal is divided into optical signals of N channels, and the optical signal of each channel is divided into a local oscillator signal and a transmitting signal after being subjected to frequency shift; transmitting the transmitting signals of N channels to a target in parallel and receiving echo signals, wherein each channel corresponds to a view field with different distances, and the transmitting/receiving view fields of each channel are completely matched to realize the center coaxiality of the view fields of each channel; echo signals and local oscillator optical signals are subjected to coherent optical mixing, intermediate frequency signals are obtained through balanced receiving, real-time parallel fast Fourier transform is performed after filtering and sampling, the synchronous measurement of distances and speeds of N channels is realized, and the fusion and output display of coaxial multi-field detection point cloud data at different distances are realized on an upper computer. The invention can simultaneously enlarge the field angle of the laser radar and improve the angular resolution, and can effectively overcome the crosstalk in the coaxial multi-field detection process.)

1. The coaxial multi-field fusion linear frequency modulation continuous wave distance and speed measuring method is characterized by comprising the following steps: at the transmitting end of the radar platform, an optical signal generated by a linear frequency modulation continuous wave laser light source is amplified and then is divided into optical signals of N channels through a 1 XN optical beam splitter, and the optical signal of each channel is divided into a local oscillation signal and a transmitting signal through the optical beam splitter; transmitting the transmitting signals of N channels to a target in parallel through optical devices of the respective channels, wherein the N channels transmit/receive in parallel, each channel corresponds to a field of view with different distances, the respective transmitting/receiving fields of each channel are completely matched, and the centers of the fields of view of each channel are coaxial; at a receiving end of the radar platform, each channel receives an echo signal of a target, the echo signal and a local oscillator optical signal are subjected to coherent optical mixing through an optical bridge, balanced receiving is adopted to obtain an intermediate frequency signal containing target distance and speed information, sampling data is obtained through filtering and sampling, and real-time parallel fast Fourier transform is carried out on the obtained sampling data of N channels by using a field programmable gate array, so that synchronous measurement of the distance and the speed of the N channels is realized, and finally fusion and output display of coaxial multi-view field detection point cloud data of different distances are realized on an upper computer.

2. The coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method according to claim 1, characterized in that: the method comprises the steps of filtering and sampling in-phase signals and orthogonal signals in intermediate frequency signals, performing Fourier transform, performing cross-spectrum processing to obtain imaginary parts, extracting the position and the positive and negative of a peak value in a frequency spectrum by using a gravity center method to obtain Doppler frequency shift generated by relative motion of a radar platform and a target, and obtaining the magnitude and the direction of radial velocity of relative motion of a transmitting end and the target distance by using the Doppler frequency shift.

3. The coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method according to claim 1, characterized in that: after the continuous coherent laser generated by a linear frequency modulation continuous wave laser light source and linearly frequency modulated by a symmetrical triangular wave is amplified by a laser amplifier, the continuous coherent laser is divided into optical signals of N channels by a 1 XN optical beam splitter; wherein, the optical signal of the nth channel firstly passes through the optical frequency shifter to shift the frequency f_nThe light field is expressed as:

wherein t is time, E₀Is the amplitude of the wave, and,t is the frequency modulation period, f₀Is the frequency-modulated initial frequency, f_{shift_n}Is the amount of frequency shift of the nth channel optical signal,for the frequency modulation rate, B is the bandwidth of the modulation band, phi_up(n) is the initial phase of the rising segment of the laser pulse of the nth channel, phi_down(n) is the initial phase of the descending segment of the n channel laser pulse, exp is an exponential function with a natural constant e as the base,

4. the coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method according to claim 3, characterized in that: after the frequency shift, the optical signal of the nth channel is split into a local oscillation signal and a transmitting signal by a 1 x 2 beam splitter;

the local oscillator signal is time delay tau_LThe optical field is represented as:

wherein E is_LIs the local oscillator signal amplitude, phi_LOIs the noise phase of the local oscillator signal;

the transmitting signal is transmitted to a target through the optical circulator, the optical scanner and the optical telescope, and an echo light beam of the target is received by the optical telescope, wherein the echo light beam is time delay tau_SExpressed as:

wherein E is_SIs the amplitude of the echo beam, phi_SIs the noise phase of the echo beam;

the optical field after the echo light beam and the local oscillator signal of the target are combined is expressed as:

time delay tau of an echo beam_STime delay tau from local oscillator signal_LThe relationship of (c) is expressed as:

where c is the speed of light, R is the distance of the target, V is the radial velocity of the relative motion of the radar platform and the target, and f_DopplerDoppler frequency shift caused by the relative motion radial velocity of the radar platform and the target;

the four outputs of the n-th channel echo light beam and the local oscillator signal after being mixed by the 2 x 490-degree optical bridge are respectively:

wherein phi is_N-nIs the mixing noise phase of the n-th channel optical signal, I_SIs a direct current quantity related to the echo beam; i is_oIs a direct current quantity related to the local oscillator signal;

the in-phase signal and the orthogonal signal with the orthogonal characteristic output by the optical bridge connector are respectively received by a photoelectric balance detector to obtain an intermediate frequency signal containing target distance and speed information; in the intermediate frequency signal of the forward frequency modulation process, the in-phase signal and the quadrature signal are respectively as follows:

in the intermediate frequency signal of the negative direction frequency modulation process, the in-phase signal and the orthogonal signal are respectively as follows:

wherein k is_inIs the response rate, k, of a photoelectric balanced detector receiving in-phase signals_quIs the response rate, phi, of a photoelectric balanced detector receiving quadrature signals_i-nAnd phi_q-nNoise phases of the in-phase signal and the quadrature signal, respectively;

the amplitudes of the in-phase and quadrature channels are replaced by:

the in-phase signal and the quadrature signal in the intermediate frequency signal in the forward frequency modulation process are simplified as follows:

in-phase signals and orthogonal signals in intermediate frequency signals in the negative direction frequency modulation process are simplified as follows:

the in-phase signal and the orthogonal signal are filtered by a low-pass filter respectively, analog-to-digital conversion is completed by an analog-to-digital converter, and then parallel fast Fourier transform is performed by field programmable gate array acquisition, wherein the Fourier transform of the in-phase signal is expressed as:

the orthogonal signal fourier transform is represented as:

performing cross-spectrum processing on the two channels:

wherein denotes a conjugate operation;

finally, only the imaginary part is taken to obtain:

Img＝δ²(f-f_n)-δ²(f+f_n)，

the frequency spectrum peak position and the positive and negative are extracted by a gravity center method, and then the intermediate frequency values in the positive frequency modulation process and the negative frequency modulation process can be respectively obtained:

from the above formula, one can obtain:

in the above formula, f_n-upIs the value of the intermediate frequency in the forward frequency modulation process, f_n-downIs the intermediate frequency value in the negative frequency modulation process;

because the Doppler frequency 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 magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift, and the magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift and are expressed as

Where λ is the wavelength of the optical signal, f_DopplerDoppler frequency shift caused by the relative motion radial velocity of the radar platform and the target;

the distance to the target point is obtained from the above equation:

in the formula (I), the compound is shown in the specification,frequency modulation rate, B frequency modulation bandwidth and T frequency modulation period;

thereby realizing the measurement of the distance and the speed of the nth channel;

and finally, synchronously measuring the distance and the speed of the N channels.

5. The coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method according to claim 4, characterized in that: the in-phase signal and the quadrature signal are filtered by a low-pass filter to remove a crosstalk signal, specifically, the crosstalk signal is represented as:

E_{S_m}amplitude of the echo beam of the mth channel, E, expressed as crosstalk_{LO_n}Representing the amplitude of a local oscillation signal corresponding to the nth channel echo light beam;

the crosstalk signal data includes a frequency of | f_{shift_n}-f_{shift_m}And the item I is filtered by a low-pass filter, so that the high-frequency crosstalk signal is eliminated, and the detection precision of the single-path optical signal is improved.

6. The coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method according to claim 1, characterized in that: the host computer realizes the fusion and output display of the coaxial multi-view field detection point cloud data at different distances; in particular, the upper computer collects the angle information of the optical scannerConverting to obtain the three-dimensional space coordinate of the target point P:

the emission frequency of the linear frequency modulation continuous wave laser light source is PRF, and the emission repetition frequency of the N split channels is also PRF; each channel corresponds to a view field with different distances, and the centers of the view fields are coaxial along the sight line direction; wherein the two-dimensional field angle of the field 1 is (H)₁,V₁) Maximum detection distance R of₁The maximum detection area isPoint cloud number density per unit area ofThe two-dimensional field angle of the field 2 is (H)₂,V₂) Maximum detection distance R₂The maximum detection area isThe density of the point cloud per unit area isThe two-dimensional field angle of the field of view 3 is (H)₃,V₃) Maximum detection distance R₃The maximum detection area isThe density of the point cloud per unit area isAnd so on;

and finally, the upper computer realizes the fusion and output display of the coaxial multi-view field detection point cloud data at different distances.

7. The device for realizing the coaxial multi-field fusion chirp continuous wave distance and speed measurement method according to any one of claims 1 to 6, is characterized in that: the optical frequency shifter comprises a laser light source (1), wherein the output end of the laser light source (1) is connected with a laser amplifier (2), and the output end of the laser amplifier (2) is connected with N optical frequency shifters (4) through a 1 XN beam splitter (3); each optical frequency shifter (4) is connected with a 1 x 2 beam splitter (5), and the 1 x 2 beam splitter (5) is connected with an optical circulator (6);

the output end of the optical circulator (6) is sequentially connected with a light beam scanner (7) and an optical telescope (8); the optical circulator (6) and the 1 multiplied by 2 beam splitter (5) are connected with an optical bridge (9); the output end of the optical bridge (9) is sequentially connected with a photoelectric balance detector (10) and a low-pass filter (11); the low-pass filter (11) is connected with a field programmable gate array (13) through an analog-to-digital converter (12); the output end of the field programmable gate array (13) is connected with an upper computer (14); the field programmable gate array (13) is also connected with the light beam scanner (7).

Technical Field

The invention relates to the technical field of laser radars, in particular to a coaxial multi-field-of-view fusion linear frequency modulation continuous wave distance and speed measurement method and device.

Background

The Frequency Modulation Continuous Wave (FMCW) laser radar combines frequency modulation continuous wave ranging and laser detection technologies in the modern radar technology, linearly modulates the frequency of a transmitting signal in a time domain, and measures the instantaneous frequency of a beat signal of an echo signal and a local oscillator signal to obtain target distance information and radial velocity information. Compared with pulse laser radar, the frequency modulation continuous wave laser radar has the advantages of synchronous distance and speed measurement, large distance/speed measurement range, high distance and speed measurement precision and the like, and is widely applied to the fields of automatic driving, high-precision three-dimensional imaging, remote sensing mapping and the like.

The light beam scanning system controls the light beam pointing of the laser radar, and projects laser pulses to the surrounding environment to form three-dimensional laser point cloud, and the light beam scanning system is a key module for determining the environmental perception capability of the laser radar. Scanning modes adopted by the laser radar currently include mechanical scanning, micro-electro-mechanical systems (MEMS) scanning and Risley scanning. By scanning the beam, the lidar system produces a uniform or non-uniform array of laser spots in a rectangular shape, an elliptical shape, or any other shape that determines the two-dimensional field of view of the lidar system, including horizontal and vertical field of view. The angular resolution is the angle between two radar data points, divided into horizontal and vertical resolution, the size of which determines the diameter of the smallest object that the lidar can detect. The number of scan lines in the horizontal and vertical field of view determines the horizontal and vertical angular resolution, respectively. For a certain angular resolution, at a close distance, the period of a scanning line is small, the density of point cloud is high, and the spatial resolution of a target is high; the farther away the distance, the greater the period of the scan line, the lower the point cloud density, and the lower the target spatial scan resolution.

On one hand, in order to realize non-blind area environment perception around the radar platform, the laser radar requires a horizontal field angle and a vertical field angle as large as possible; on the other hand, in order to ensure that distant objects (such as pedestrians, vehicles) can be resolved effectively, there must be sufficient horizontal and vertical angular resolution.

The prior mechanical scanning lidar is based on a mature rotating mirror, capable of employing mechanical rotation in the horizontal direction and non-mechanical optical scanning by stacking in the vertical direction, with the vertical angular resolution determined by the spacing between two adjacent modules and the focal length of the optical system. In order to improve horizontal and vertical angular resolution, the mechanical scanning lidar needs to continuously improve the transmitting frequency and the number of scanning lines, and the space scanning resolution of long-distance detection is met by dense scanning. However, the scheme requires that the high-frequency laser radars are densely arranged in the vertical direction, not only has large size and high cost, but also has high requirements on heat dissipation, process and the like. In the prior MEMS scanning laser radar, the emission angle of a single emitter is changed in a micro-vibration mirror mode for scanning, micron-scale area array scanning is realized, the structure is simple, the size is small, the vertical angle resolution can reach 0.1 degree, and the scanning mode can be dynamically adjusted, so that a specific object is focused, and the detailed information of more and less objects is collected and identified. However, because the field angle of a single MEMS is small, a multi-field splicing method is required to enlarge the field of view, and the controllable realization of the high-frequency vibration of the micro-galvanometer is difficult, so that the requirements on hardware are high, and the cost is high. The Risley prism generally consists of two or more coaxial wedge prisms, and can accurately control the direction of a light beam by controlling the relative rotation of the prisms, so that high-precision two-dimensional scanning in a large angle range is realized. However, a complex nonlinear relationship is presented between the adjustment of the respective rotation angles of two prisms in the Risley prism and the change of the motion track of the emergent light beam, and the generated point cloud is very uneven in distribution.

In the prior art, regardless of the scanning method adopted by the laser radar, the angle of view can be enlarged and the angular resolution can be improved by the following method. The first method is that the modulation period of the emission signal is compressed to improve the emission repetition frequency, so that the angular resolution of the laser radar system can be improved under a certain scanning field angle, but the broadband linear frequency modulation with high repetition frequency and high linearity is difficult to realize; the second method is to improve the scanning field angle of the lidar system at a certain angular resolution by splicing multiple radar fields, but the cost is high, and the crosstalk between multiple paths needs to be eliminated. The laser radar device for measuring distance and speed, which can simultaneously enlarge the field angle and improve the angular resolution, has not been reported so far.

Disclosure of Invention

The invention aims to provide a coaxial multi-field-of-view fused linear frequency modulation continuous wave distance and speed measuring method. The invention can realize the coaxial multi-field fusion detection at different distances (namely far distance, middle distance and near distance), can simultaneously enlarge the field angle and improve the angular resolution, and can effectively overcome the crosstalk in the coaxial multi-field detection process.

The technical scheme of the invention is as follows: a distance and speed measurement method for coaxial multi-field fusion linear frequency modulation continuous wave comprises the steps that at the transmitting end of a radar platform, an optical signal generated by a linear frequency modulation continuous wave laser light source is amplified and then divided into optical signals of N channels through a 1 x N optical beam splitter, the optical signal of each channel is subjected to frequency shift firstly and then divided into a local oscillator signal and a transmitting signal through the optical beam splitter; transmitting the transmitting signals of N channels to a target in parallel through optical devices of the respective channels, wherein the N channels transmit/receive in parallel, each channel corresponds to a field of view with different distances, the respective transmitting/receiving fields of each channel are completely matched, and the centers of the fields of view of each channel are coaxial; at a receiving end of a radar platform, each channel receives an echo signal of a target, the echo signal and a local oscillator optical signal are subjected to coherent optical mixing through an optical bridge, balanced receiving is adopted to obtain an intermediate frequency signal containing target distance and speed information, sampling data is obtained through filtering and sampling, and a field programmable gate array is used for carrying out real-time parallel fast Fourier transform on the obtained sampling data of N channels, so that the synchronous measurement of the distance and the speed of the N channels is realized, and finally the fusion and the output display of coaxial multi-view field detection point cloud data at different distances (namely far distance, medium distance and near distance) are realized on an upper computer.

The coaxial multi-field fusion linear frequency modulation continuous wave distance and speed measurement method realizes synchronous measurement of distances and speeds of N channels, and specifically comprises the steps of filtering and sampling in-phase signals and orthogonal signals in intermediate frequency signals, respectively carrying out Fourier transform, then carrying out cross-spectrum processing to obtain imaginary parts of the signals, extracting the position and the positive and negative of a peak value in a frequency spectrum by using a gravity center method to obtain Doppler frequency shift generated by 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 a transmitting end and the target distance by using the Doppler frequency shift.

In the coaxial multi-field-of-view fusion linear frequency modulation continuous wave distance and speed measuring method, a linear frequency modulation continuous wave laser light source generates symmetrical triangular wave linear frequency modulation continuous coherent laser, the symmetrical triangular wave linear frequency modulation continuous coherent laser is amplified by a laser amplifier, and then the laser is divided into optical signals of N channels by a 1 XN optical beam splitter; wherein, the optical signal of the nth channel firstly passes through the optical frequency shifter to shift the frequency f_nThe light field is expressed as:

wherein t is time, E₀Is the amplitude, T is the frequency modulation period, f₀Is the frequency-modulated initial frequency, f_{shift_n}Is the amount of frequency shift of the nth channel optical signal,for the frequency modulation rate, B is the bandwidth of the modulation band, phi_up(n) is the initial phase of the rising segment of the laser pulse of the nth channel, phi_down(n) is the initial phase of the descending segment of the n channel laser pulse, exp is an exponential function with a natural constant e as the base,

in the coaxial multi-field-of-view fusion linear frequency modulation continuous wave distance and speed measuring method, the optical signal of the nth channel is subjected to frequency shift and then split into the local oscillator signal and the transmitting signal by the 1 × 2 beam splitter;

the local oscillator signal is time delay tau_LThe optical field is represented as:

wherein E is_LIs the local oscillator signal amplitude, phi_LOIs the noise phase of the local oscillator signal;

the transmitting signal is transmitted to a target through the optical circulator, the optical scanner and the optical telescope, and an echo light beam of the target is received by the optical telescope, wherein the echo light beam is time delay tau_SExpressed as:

wherein E is_SIs the amplitude of the echo beam, phi_SIs the noise phase of the echo beam;

the optical field after the echo light beam and the local oscillator signal of the target are combined is expressed as:

time delay tau of an echo beam_STime delay tau from local oscillator signal_LThe relationship of (c) is expressed as:

where c is the speed of light, R is the distance of the target, V is the radial velocity of the relative motion of the radar platform and the target, and f_DopplerIs the Doppler shift caused by the relative motion radial velocity of the radar platform and the target,

the four outputs of the n-th channel echo light beam and the local oscillator signal after being mixed by the 2 x 490-degree optical bridge are respectively:

wherein phi is_N-nIs the mixing noise phase of the n-th channel optical signal, I_SIs a direct current quantity related to the echo beam; i is_oIs a direct current quantity related to the local oscillator signal;

the in-phase signal and the orthogonal signal with the orthogonal characteristic output by the optical bridge connector are respectively received by a photoelectric balance detector to obtain an intermediate frequency signal containing target distance and speed information; in the intermediate frequency signal of the forward frequency modulation process, the in-phase signal and the quadrature signal are respectively as follows:

in the intermediate frequency signal of the negative direction frequency modulation process, the in-phase signal and the orthogonal signal are respectively as follows:

wherein k is_inIs the response rate, k, of a photoelectric balanced detector receiving in-phase signals_quIs the response rate, phi, of a photoelectric balanced detector receiving quadrature signals_i-nAnd phi_q-nNoise phases of the in-phase signal and the quadrature signal, respectively;

the amplitudes of the in-phase and quadrature channels are replaced by:

the in-phase signal and the quadrature signal in the intermediate frequency signal in the forward frequency modulation process are simplified as follows:

in-phase signals and orthogonal signals in intermediate frequency signals in the negative direction frequency modulation process are simplified as follows:

the in-phase signal and the orthogonal signal are filtered by a low-pass filter respectively, analog-to-digital conversion is completed by an analog-to-digital converter, and then parallel fast Fourier transform is performed by field programmable gate array acquisition, wherein the Fourier transform of the in-phase signal is expressed as:

the orthogonal signal fourier transform is represented as:

performing cross-spectrum processing on the two channels:

wherein denotes a conjugate operation;

finally, only the imaginary part is taken to obtain:

Img＝δ²(f-f_n)-δ²(f+f_n)，

the frequency spectrum peak position and the positive and negative are extracted by a gravity center method, and then the intermediate frequency values in the positive frequency modulation process and the negative frequency modulation process can be respectively obtained:

from the above formula, one can obtain:

in the above formula, f_n-upIs the value of the intermediate frequency in the forward frequency modulation process, f_n-downIs the intermediate frequency value in the negative frequency modulation process;

because the Doppler frequency 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 magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift, and the magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift and are expressed as

Where λ is the wavelength of the optical signal, f_DopplerDoppler frequency shift caused by the relative motion radial velocity of the radar platform and the target;

the distance to the target point is obtained from the above equation:

in the formula (I), the compound is shown in the specification,frequency modulation rate, B frequency modulation bandwidth and T frequency modulation period;

thereby realizing the measurement of the distance and the speed of the nth channel;

and finally, synchronously measuring the distance and the speed of the N channels.

In the coaxial multi-field-of-view fused chirp continuous wave distance and speed measuring method, the in-phase signal and the quadrature signal are filtered by the low-pass filter to remove the crosstalk signal, specifically, the crosstalk signal is represented as:

E_{S_m}amplitude of the echo beam of the mth channel, E, expressed as crosstalk_{LO_n}Representing the amplitude of the local oscillation signal corresponding to the nth echo light beam;

the crosstalk signal data includes a frequency of | f_{shift_n}-f_{shift_m}And the item I is filtered by a low-pass filter, so that the high-frequency crosstalk signal is eliminated, and the detection precision of the single-path optical signal is improved.

In the coaxial multi-view-field fusion linear frequency modulation continuous wave distance and speed measuring method, the upper computer realizes fusion and output display of the coaxial multi-view-field detection point cloud data at different distances, and specifically, the upper computer collects the angle information of the optical scannerConverting to obtain the three-dimensional space coordinate of the target point P:

the emission frequency of the linear frequency modulation continuous wave laser light source is PRF, and the emission repetition frequency of the N split channels is also PRF; each channel corresponds to a view field with different distances, and the centers of the view fields are coaxial along the sight line direction; wherein the two-dimensional field angle of the field 1 is (H)₁,V₁) Maximum detection distance R of₁The maximum detection area isPoint cloud number density per unit area ofThe two-dimensional field angle of the field 2 is (H)₂,V₂) Maximum detection distance R₂The maximum detection area isThe density of the point cloud per unit area isThe two-dimensional field angle of the field of view 3 is (H)₃,V₃) Maximum detection distance R₃The maximum detection area isThe density of the point cloud per unit area isAnd so on;

and finally, the upper computer realizes the fusion and output display of the coaxial multi-view field detection point cloud data at different distances.

The device for realizing the distance and speed measurement method of the coaxial multi-field fusion linear frequency modulation continuous wave comprises a laser light source, wherein the output end of the laser light source is connected with a laser amplifier, and the output end of the laser amplifier is connected with N optical frequency shifters through a 1 XN beam splitter; each optical frequency shifter is connected with a 1 x 2 beam splitter, and the 1 x 2 beam splitter is connected with an optical circulator;

the output end of the optical circulator is sequentially connected with a light beam scanner and an optical telescope; the optical circulator and the 1 multiplied by 2 beam splitter are connected with an optical bridge together; the output end of the optical bridge is sequentially connected with a photoelectric balance detector and a low-pass filter; the low-pass filter is connected with a field programmable gate array through an analog-to-digital converter; the output end of the field programmable gate array is connected with an upper computer; the field programmable gate array is also connected with the light beam scanner.

Compared with the prior art, the optical signal generated by the linear frequency modulation continuous wave laser light source is amplified and then divided into optical signals of N channels through the 1 XN optical beam splitter, and the optical signal of each channel is divided into a local oscillation signal and a transmitting signal through the optical beam splitter after being subjected to frequency shift; transmitting the transmitting signals of N channels to a target in parallel through optical devices of the respective channels, wherein the N channels transmit/receive in parallel, each channel corresponds to a field of view with different distances, the respective transmitting/receiving fields of each channel are completely matched, and the centers of the fields of view of each channel are coaxial; (ii) a At a receiving end of a radar platform, each channel receives an echo signal of a target, the echo signal and a local oscillator optical signal are subjected to coherent optical mixing through an optical bridge, balanced receiving is adopted to obtain an intermediate frequency signal containing target distance and speed information, sampling data is obtained through filtering and sampling, and a field programmable gate array is used for carrying out real-time parallel fast Fourier transform on the obtained sampling data of N channels, so that the synchronous measurement of the distance and the speed of the N channels is realized, and finally the fusion and the output display of coaxial multi-view field detection point cloud data at different distances (namely far distance, medium distance and near distance) are realized on an upper computer. The invention adopts the coaxial multi-field fusion, can simultaneously enlarge the field angle of the laser radar and improve the angular resolution, can effectively overcome the crosstalk in the coaxial multi-field detection process, and has good development prospect in the fields of vehicle-mounted, airborne, satellite-borne and the like.

Drawings

FIG. 1 is a schematic structural view of the present invention;

fig. 2 shows a schematic diagram of a waveform relationship and a frequency difference between echoes of a symmetric triangular chirp continuous wave and a local oscillator signal;

FIG. 3 is a schematic diagram of a scanning field coordinate system of a laser radar;

fig. 4 shows a far, middle and near coaxial multi-field schematic diagram.

The labels in the figures are: 1. a laser light source; 2. a laser amplifier; 3. a 1 XN beam splitter; 4. an optical frequency shifter; 5. a 1 × 2 beam splitter; 6. an optical circulator; 7. a light beam scanner; 8. an optical telescope; 9. an optical bridge; 10. a photoelectric balance detector; 11. a low-pass filter; 12. an analog-to-digital converter; 13. a field programmable gate array; 14. and (4) a host computer.

Detailed Description

The invention is further illustrated by the following figures and examples, which are not to be construed as limiting the invention.

Example 1: a distance and speed measurement method for coaxial multi-field fusion linear frequency modulation continuous wave comprises the steps that at the transmitting end of a radar platform, an optical signal generated by a linear frequency modulation continuous wave laser light source is amplified and then divided into optical signals of N channels through a 1 x N optical beam splitter, the optical signal of each channel is subjected to frequency shift firstly and then divided into a local oscillator signal and a transmitting signal through the optical beam splitter; transmitting the transmitting signals of N channels to a target in parallel through optical devices of the respective channels, wherein the N channels transmit/receive in parallel, each channel corresponds to a field of view with different distances, the respective transmitting/receiving fields of each channel are completely matched, and the centers of the fields of view of each channel are coaxial; at a receiving end of a radar platform, each channel receives an echo signal of a target, the echo signal and a local oscillator optical signal are subjected to coherent optical mixing through an optical bridge, balanced reception is adopted to obtain an intermediate frequency signal containing target distance and speed information, filtering and sampling are carried out to obtain sampling data, a field programmable gate array is used for carrying out real-time parallel fast Fourier transform on the obtained sampling data of N channels, so that synchronous measurement of the distance and the speed of the N channels is realized, specifically, after filtering and sampling processing are carried out on in-phase signals and orthogonal signals in the intermediate frequency signal, Fourier transform is respectively carried out, cross spectrum processing is carried out to obtain an imaginary part of the in-phase signals and the orthogonal signals, the position and the positive and negative of a peak value in a frequency spectrum are extracted by using a gravity center method, Doppler frequency shift generated by relative motion of the radar platform and the target is obtained, and then the size and the direction of the radial speed of relative motion of a transmitting end and the target are obtained by the Doppler frequency shift A distance; and finally, realizing the fusion and output display of the coaxial multi-field detection point cloud data at different distances (namely far distance, middle distance and near distance) on an upper computer.

The device for realizing the method comprises a laser light source 1, wherein the output end of the laser light source 1 is connected with a laser amplifier 2, and the output end of the laser amplifier 2 is connected with N optical frequency shifters 4 through a 1 XN beam splitter 3; each optical frequency shifter 4 is connected with a 1 × 2 beam splitter 5, and the 1 × 2 beam splitter 5 is connected with an optical circulator 6; the output end of the optical circulator 6 is sequentially connected with a light beam scanner 7 and an optical telescope 8; the optical circulator 6 and the 1 multiplied by 2 beam splitter 5 are connected with an optical bridge 9; the output end of the optical bridge 9 is connected with an optical balance detector 10 and a low-pass filter 11 in sequence; the low-pass filter 11 is connected with a field programmable gate array 13 through an analog-to-digital converter 12; the output end of the field programmable gate array 13 is connected with an upper computer 14; the main field programmable gate array 13 is also connected to the beam scanner 7 for controlling the beam scanner 7. The host computer 14 realizes the fusion and output display of the coaxial multi-view field detection point cloud data at different distances (namely far distance, middle distance and near distance) and other sensor data acquisition and decision-making tasks.

Example 2: a coaxial multi-field fusion linear frequency modulation continuous wave distance and speed measurement method is shown in figure 1 and comprises a linear frequency modulation continuous wave laser light source 1, a 1550nm single-mode narrow-line-width optical fiber laser which is safe to human eyes is adopted, the line width of the laser is 10kHz, the output power is 20mW, the optical fiber output is provided with isolation protection, a frequency mixing signal of a frequency modulation signal generated by a frequency modulation signal generator and a fundamental frequency signal generated by a fundamental frequency signal generator is adopted as a radio frequency driving signal of an optical fiber phase modulator, the optical fiber phase modulator is driven to generate a frequency modulation laser signal, symmetrical triangular wave linear modulation is adopted, the frequency of the modulation signal changes in a symmetrical triangular shape along with time, the first half part is called as positive frequency modulation, and the second half part is called as negative frequency modulation in one period. FIG. 2 shows a schematic diagram of waveform relationship and frequency difference between echo and local oscillator signal of symmetric triangular linear frequency modulated continuous wave, and an optical filter is used to suppress harmonic waves and retain frequency modulated laser signals of required order, the frequency modulated bandwidth of the generated frequency modulated continuous wave laser is 2.5GHz, and the frequency modulated rate is 5 × 10¹⁶Hz/s, frequency modulation period of 10 mus, and repetition frequency of 100 kHz. The linear frequency modulation continuous wave laser light source 1 generates symmetrical triangular wave linear frequency modulation continuous coherent laser, the polarization extinction ratio is ensured to be more than 25dB through the online polarization/controller, and the continuous coherent laser is amplified through the laser amplifier 2The power of the 1 st channel is about 50mW, the power of the 2 nd channel is about 300mW, and the power of the 3 rd channel is about 600mW in consideration of insertion loss;

wherein, the optical signal of the nth channel firstly passes through the optical frequency shifter 4 to shift the frequency f_nThe light field is expressed as:

wherein t is time, E₀Is the amplitude, T is the frequency modulation period, f₀Is the frequency-modulated initial frequency, f_{shift_n}Is the amount of frequency shift of the nth channel optical signal,for the frequency modulation rate, B is the bandwidth of the modulation band, phi_up(n) is the initial phase of the rising segment of the laser pulse of the nth channel, phi_down(n) is the initial phase of the descending segment of the n channel laser pulse, exp is an exponential function with a natural constant e as the base,

after the frequency shift, the optical signal of the nth channel is split into a local oscillation signal and a transmitting signal by a 1 x 2 beam splitter;

the local oscillation signal is a linear frequency modulation signal with time delay tau L, and the optical field is expressed as:

wherein E is_LIs the local oscillator signal amplitude, phi_LOIs the noise phase of the local oscillator signal;

the transmitting signal is transmitted to a target through the optical circulator, the optical scanner and the optical telescope, and an echo light beam of the target is received by the optical telescope, wherein the echo light beam is time delay tau_SExpressed as:

wherein E is_SIs the amplitude of the echo beam, phi_SIs the noise phase of the echo beam;

in this embodiment, the 1 st channel is divided into a local oscillation beam and a transmission beam by a 1 × 2 fiber splitter without frequency shift, a small amount of energy (about 2mW) is used as a local oscillation signal, a large amount of energy (about 45mW) is used as a transmission signal, and each path passes through a three-port fiber circulator 6 and then is transmitted to a target through a MEMS scanner (beam scanner 7). The method of splicing 3 MEMS horizontal fields is adopted, each MEMS field is 20 degrees multiplied by 20 degrees, the combined field is 60 degrees multiplied by 20 degrees (horizontal multiplied by vertical), the MEMS transmitting aperture is 3mm, and no transmitting/receiving telescope is provided. MEMS adopts line-by-line scanning, slow axis triangular wave in the vertical direction, fast axis resonance in the horizontal direction, 100 lines of vertical scanning lines and 10Hz of frame frequency.

The 2 nd channel is firstly subjected to frequency shift of 500MHz through an optical fiber frequency shifter, then is divided into a local oscillation light beam and an emission light beam through a 1X 2 optical beam splitter, a small part of energy is used as a local oscillation signal, a large part of energy is used as an emission signal, the emission signal passes through a three-port optical fiber circulator and is emitted to a target through an MEMS scanner, the MEMS field of view is 20 degrees multiplied by 10 degrees, the effective emission aperture of the MEMS is 3mm, and no transmitting/receiving telescope is provided. MEMS adopts line-by-line scanning, slow axis triangular wave in the vertical direction, fast axis resonance in the horizontal direction, 100 lines of vertical scanning lines and 10Hz of frame frequency.

The 3 rd channel is firstly subjected to frequency shift of 1GHz by the optical fiber frequency shifter, then is divided into a local oscillation light beam and a transmission light beam by the 1X 2 optical beam splitter, a small part of energy is used as the local oscillation signal, a large part of energy is used as the transmission signal, the transmission signal passes through the three-port optical fiber circulator and is transmitted to a target by the MEMS scanner, the MEMS view field is 20 degrees multiplied by 10 degrees, the effective transmission aperture of the MEMS is 5mm, the aperture of the transmission/reception telescope is 18mm, the multiplying power is 4 times, and the total view field is 5 degrees multiplied by 2.5 degrees. MEMS adopts line-by-line scanning, slow axis triangular wave in the vertical direction, fast axis resonance in the horizontal direction, 100 lines of vertical scanning lines and 10Hz of frame frequency.

The 1 st channel corresponds to a field of view within 50 meters, the 2 nd channel corresponds to a field of view within 100 meters, and the 3 rd channel corresponds to a field of view within 300 meters. The perfect match of the respective transmit/receive fields of view for each channel, the fields of view for the 3 channels achieve perfect central co-axial.

Each channel target echo light beam and local oscillator light are input into a 2 x 490-degree optical fiber bridge to realize orthogonal coherent reception, wherein the optical field after the echo light beam and the local oscillator signal of the target are combined is represented as follows:

time delay tau of an echo beam_STime delay tau from local oscillator signal_LThe relationship of (c) is expressed as:

where c is the speed of light, R is the distance of the target, V is the radial velocity of the relative motion of the radar platform and the target, and f_DopplerIs the Doppler shift caused by the relative motion radial velocity of the radar platform and the target,

the four outputs of the echo light beam and the local oscillator signal after being mixed by the 2 x 490-degree optical bridge are respectively:

wherein phi is_N-nIs the mixing noise phase of the n-th channel optical signal, I_SIs a direct current quantity related to the echo beam; i is_oIs a direct current quantity related to the local oscillator signal;

the in-phase signal and the orthogonal signal with the orthogonal characteristic output by the optical bridge connector are respectively received by a photoelectric balance detector to obtain an intermediate frequency signal containing target distance and speed information; in the intermediate frequency signal of the forward frequency modulation process, the in-phase signal and the quadrature signal are respectively as follows:

in the intermediate frequency signal of the negative direction frequency modulation process, the in-phase signal and the orthogonal signal are respectively as follows:

wherein k is_inIs the response rate, k, of a photoelectric balanced detector receiving in-phase signals_quIs the response rate, phi, of a photoelectric balanced detector receiving quadrature signals_i-nAnd phi_q-nNoise phases of the in-phase signal and the quadrature signal, respectively;

the amplitudes of the in-phase and quadrature channels are replaced by:

the in-phase signal and the quadrature signal in the intermediate frequency signal in the forward frequency modulation process are simplified as follows:

in-phase signals and orthogonal signals in intermediate frequency signals in the negative direction frequency modulation process are simplified as follows:

the in-phase signal and the orthogonal signal are filtered by a low-pass filter respectively, analog-to-digital conversion is completed by an analog-to-digital converter, and then parallel fast Fourier transform is performed by field programmable gate array acquisition, wherein the Fourier transform of the in-phase signal is expressed as:

the orthogonal signal fourier transform is represented as:

performing cross-spectrum processing on the two channels:

wherein denotes a conjugate operation;

finally, only the imaginary part is taken to obtain:

Img＝δ²(f-f_n)-δ²(f+f_n)，

the frequency spectrum peak position and the positive and negative are extracted by a gravity center method, and then the intermediate frequency values in the positive frequency modulation process and the negative frequency modulation process can be respectively obtained:

from the above formula, one can obtain:

in the above formula, f_n-upIs the value of the intermediate frequency in the forward frequency modulation process, f_n-downIs the intermediate frequency value in the negative frequency modulation process;

because the Doppler frequency 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 magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift, and the magnitude and the direction of the relative motion radial velocity of the radar platform and the target can be obtained by the Doppler frequency shift and are expressed as

Where λ is the wavelength of the optical signal, f_DopplerDoppler frequency shift caused by the relative motion radial velocity of the radar platform and the target;

the distance to the target point is obtained from the above equation:

in the formula (I), the compound is shown in the specification,frequency modulation rate, B frequency modulation bandwidth and T frequency modulation period;

thereby realizing the measurement of the distance and the speed of the nth channel;

finally, the synchronous measurement of the distance and the speed of 3 channels is realized.

In this case, since crosstalk occurs between multiple channels, the in-phase signal and the quadrature signal are filtered by low-pass filters to remove crosstalk signals, specifically, the crosstalk signals are expressed as:

E_{S_m}amplitude of the echo beam, E, expressed as crosstalk_{LO_n}Representing the amplitude of the local oscillation signal corresponding to the nth echo light beam;

the crosstalk signal data includes a frequency of | f_{shift_n}-f_{shift_m}The I term is filtered by a low-pass filter to eliminate high-frequency stringsAnd disturbing the signal, and improving the detection precision of the single-path optical signal.

After the synchronous measurement of the distance and the speed of N channels is realized, the angle information of the optical scanner collected by the upper computerAs shown in fig. 3, the three-dimensional space coordinates of the target point P are obtained by conversion:

the emission frequency of the linear frequency modulation continuous wave laser light source is PRF, and the emission repetition frequency of the N split channels is also PRF; each channel corresponds to a view field with different distances, and the centers of the view fields are coaxial along the sight line direction; as shown in FIG. 4, the two-dimensional field angle of the field 1 is (H)₁,V₁) Maximum detection distance R of₁The maximum detection area isPoint cloud number density per unit area ofThe two-dimensional field angle of the field 2 is (H)₂,V₂) Maximum detection distance R₂The maximum detection area isThe density of the point cloud per unit area isThe two-dimensional field angle of the field of view 3 is (H)₃,V₃) Maximum detection distance R₃The maximum detection area isThe density of the point cloud per unit area isAnd so on;

and finally, the upper computer realizes the fusion and output display of the far, middle and close distance coaxial multi-field detection point cloud data. In this embodiment, the specific parameters of the far-middle-near three-gear scanning are as follows:

first stage, field of view 5 ° × 2.5 °, emission aperture 18mm, angular resolution 0.05 ° × 0.025 ° (horizontal × vertical), maximum detection distance 300m, maximum detection area s₁＝26.17m×13.08m＝303.06m²For a pedestrian 1.70 meters high at 300 meters, 14 lines can be detected.

Second, the field of view is 20 degrees multiplied by 10 degrees, the emission aperture is 3mm, the angular resolution is 0.2 degrees multiplied by 0.1 degree, the maximum detection distance is 100 meters, and the maximum detection area is s₂＝34.73m×17.43m＝605.34m²For a pedestrian 1.70 meters high at 100 meters, 10 lines can be detected;

third, the field of view is 60 degrees multiplied by 20 degrees, the emission aperture is 3mm, the angular resolution is 0.2 degrees multiplied by 0.2 degrees, the maximum detection distance is 50 meters, and the maximum detection area is s₂＝50m×17.36m＝868.24m²For a pedestrian 50 meters high by 1.70 meters, 10 lines can be detected.

In conclusion, the invention adopts the coaxial multi-field fusion, can simultaneously expand the field angle and improve the angular resolution, can effectively overcome the crosstalk in the coaxial multi-field detection process, and can realize the broadband linear frequency modulation with high repetition frequency and high linearity. The method has good development prospect in the fields of vehicle-mounted, airborne, satellite-borne and the like.