CN106707291B - Double-frequency linear frequency modulation coherent wind lidar - Google Patents
Double-frequency linear frequency modulation coherent wind lidar Download PDFInfo
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- CN106707291B CN106707291B CN201611130242.8A CN201611130242A CN106707291B CN 106707291 B CN106707291 B CN 106707291B CN 201611130242 A CN201611130242 A CN 201611130242A CN 106707291 B CN106707291 B CN 106707291B
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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
- G01S17/50—Systems of measurement based on relative movement of target
- G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
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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
- G01S17/34—Systems determining position data of a target for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated using transmission of continuous, frequency-modulated waves while heterodyning the received signal, or a signal derived therefrom, with a locally-generated signal related to the contemporaneously transmitted signal
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- Optical Radar Systems And Details Thereof (AREA)
Abstract
The embodiment of the invention discloses a laser radar system, which comprises a light source module, a modulation optical module, a transmitting and receiving module, a detection module and a signal processing module, wherein the modulation optical module is used for modulating light; the dual-wavelength laser beam is converted into a dual-frequency linear frequency modulation continuous wave laser beam through linear modulation of a modulation optical module; one beam of light is used as a local oscillation light beam, the other beam of light is used as signal light interacted with a detection target, and the signal light is scattered to an echo signal by the detection target; and obtaining dual-wavelength Doppler frequency shift difference information by carrying out coherent beat frequency on the local oscillator light beam and the echo signal. This application technical scheme adopts dual wavelength linear frequency modulation laser, has greatly reduced non-linear frequency modulation and atmospheric turbulence effect to the influence of speed measurement resolution ratio, has realized finding range and measuring speed to surveying the target simultaneously, has advantages such as detection precision height, anti-electromagnetic interference, no distance blind area.
Description
Technical Field
The invention relates to the field of radars, in particular to a double-frequency linear frequency modulation coherent wind lidar.
Background
With the development of optical technology, the laser radar has the advantages of good directivity, high time resolution and spatial resolution, high precision, non-contact measurement and the like, so that the laser radar is rapidly developed and widely applied in the fields of navigation, aerospace, meteorological element measurement, atmospheric environment monitoring and the like.
The laser radar is a radar system for detecting characteristic quantities such as position, speed and the like of a target by emitting laser beams, and mainly comprises a laser transmitter, an optical receiver, an information processing system and the like. By emitting a detection signal (laser beam) to a target and then correspondingly processing a received signal (target echo) reflected from the target and the emission signal, relevant information of the target, such as target distance, azimuth, height, speed, attitude, even shape and other parameters, can be obtained, so that the detection, tracking and identification of the targets such as airplanes, missiles and the like are realized.
The double-frequency coherent laser radar is a radar system for inverting the speed of a measured target by detecting the difference of double-wavelength Doppler frequency shifts through coherent beat frequency, information needs to be extracted and converted from the Doppler frequency shifts into Doppler frequency shift difference values, Doppler frequency shift spectral line broadening caused by speckle noise is inhibited, the influence of the speckle noise on speed measurement resolution caused by atmospheric turbulence is greatly reduced, and a signal processing link is converted from a light path part into a technically mature circuit part. The device can realize short-distance or long-distance accurate speed measurement, and has great application potential in the fields of remote or portable detection, atmospheric remote sensing and the like. But the dual-frequency coherent laser radar is difficult to realize simultaneous distance measurement and speed measurement. On the other hand, the distance resolution of the traditional laser radar is extremely high after the linear frequency modulation technology is applied, and the laser radar has important application in close-range precision detection, three-dimensional distance imaging and autonomous safe soft landing of a space capsule, but the actual distance measurement resolution and speed measurement resolution of the system are seriously influenced by the nonlinear frequency modulation and the atmospheric turbulence effect.
Disclosure of Invention
The embodiment of the invention aims to provide a double-frequency linear frequency modulation coherent wind lidar which can realize distance measurement and speed measurement on a measured target, greatly reduce the influence of nonlinear frequency sweep and atmospheric turbulence effect on speed measurement resolution, and has the advantages of high distance resolution and speed resolution, electromagnetic interference resistance and no distance blind area.
In order to solve the above technical problems, embodiments of the present invention provide the following technical solutions:
the embodiment of the invention provides a double-frequency linear frequency modulation coherent wind lidar, which comprises:
the device comprises a light source module, a modulation optical module, a transmitting and receiving module, a detection module and a signal processing module;
the light source module is used for emitting a dual-wavelength laser beam with a preset wavelength;
the modulation optical module is used for carrying out linear modulation on the dual-wavelength laser beam to emit a dual-frequency linear frequency modulation continuous wave laser beam;
the transmitting and receiving module is used for dividing the dual-frequency linear frequency modulation continuous wave laser beam into a first laser beam and a second laser beam, the first laser beam is incident to a detection target, and the second laser beam is used as a local oscillation light beam; receiving the backscatter echo signal of the probe target;
the detection module is used for carrying out optical beat frequency on the local oscillator light beam and the echo signal so as to obtain Doppler frequency shift information and simultaneously converting an optical signal into an electric signal;
the signal processing module is used for performing microwave beat frequency on the electric signal to obtain Doppler frequency shift difference information;
the modulation optical module comprises a modulator and a signal generator; the modulator is used for carrying out linear frequency modulation on the dual-wavelength laser beam; the signal generator is connected with the modulator and used for providing a modulation signal for the modulator, and the signal generator is a triangular wave signal generator to generate triangular wave modulation information;
the signal processing module comprises an acquisition card and a data processing device; the acquisition card is connected with the balance detector and is used for acquiring signals; and the data processing device is connected with the acquisition card and is used for performing microwave beat frequency on the electric signal to obtain a dual-frequency Doppler frequency shift difference signal so as to invert the distance and speed information of the target and eliminate an error term generated by the nonlinear frequency modulation effect.
Preferably, the modulation optical module further includes:
and the filter is connected with the modulator and is used for filtering background noise in the dual-frequency linear frequency modulation continuous wave laser beam.
Preferably, the modulation optical module further includes:
and the laser amplifier is connected with the filter and used for amplifying the energy of the filtered double-frequency linear frequency modulation continuous wave laser beam.
Preferably, the transmitting and receiving module includes:
the optical fiber coupling device comprises a first beam splitter, a second beam splitter, an optical transceiver and a circulator;
the first beam splitter is connected with the laser amplifier and is used for splitting the dual-frequency linear frequency modulation continuous wave laser beam into the first laser beam and the second laser beam;
the circulator is respectively connected with the optical transceiver, the first beam splitter and the optical fiber
The second beam splitter is connected and used for enabling the first laser beam to be incident to the optical transceiver and enabling the second laser beam to be incident to the second beam splitter; and the echo signal is incident to the second beam splitter;
the optical transceiver is used for enabling the first laser beam to be incident on the detection target, receiving an echo signal scattered after interaction with the detection target and enabling the echo signal to be incident on the circulator;
the second beam splitter is used for enabling the echo signal and the second laser beam to be incident to the detection module.
Preferably, the detection module includes: and the balance detector is connected with the second beam splitter and is used for carrying out optical beat frequency on the second laser beam and the echo signal so as to obtain a dual-frequency Doppler frequency shift signal.
Preferably, the transmitting and receiving module further comprises:
and the attenuators are respectively connected with the first beam splitter and the second beam splitter and are used for attenuating the second laser beam, and the attenuated beam is used as the local oscillation light beam.
Preferably, the data processing apparatus includes:
DSP data processing unit and computer.
The embodiment of the invention provides a double-frequency linear frequency modulation coherent wind lidar which comprises a light source module, a modulation optical module, a transmitting and receiving module, a detection module and a signal processing module, wherein the light source module is used for emitting light; the dual-wavelength laser beam is converted into a dual-frequency linear frequency modulation continuous wave laser beam through linear modulation of a modulation optical module; one beam of light is used as a local oscillation light beam, and the other beam of light is used for interacting with a detection target and scattering an echo signal through the detection target; and obtaining dual-wavelength Doppler frequency shift difference information by carrying out coherent beat frequency on the local oscillator light beam and the echo signal.
According to the technical scheme, the dual-wavelength linear frequency modulation laser is adopted, and the system structure and the signal processing part are simpler than those of the prior art; because the atmospheric turbulence has the same influence on the two frequency modulation beams, the influence of speckle noise caused by the unevenness of a detection target and the atmospheric turbulence effect is reduced; because linear continuous waves are adopted as coherent light beams, the distance resolution is high, and no blind area exists in the distance; in addition, the distance measurement and speed measurement can be simultaneously carried out on the detection target. The method comprises the following steps of further performing microwave beat frequency on the basis of optical beat frequency to obtain Doppler frequency shift difference information, wherein any error term simultaneously acting on the phases of two linear frequency modulation signals with different frequencies cannot influence the phase of a difference frequency signal obtained by the microwave beat frequency, so that the problem of non-linearity of frequency sweep is solved; the frequency of the difference frequency signal is much lower than that of an intermediate frequency signal commonly used in daily life, so that the frequency-difference frequency signal can resist electromagnetic interference to a certain extent.
Drawings
In order to more clearly illustrate the embodiments or technical solutions of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained based on these drawings without creative efforts.
Fig. 1 is a block diagram of a dual-frequency chirp coherent wind lidar according to an embodiment of the present invention;
FIG. 2 is a system diagram illustrating an exemplary application scenario according to an embodiment of the present invention;
fig. 3 is a schematic diagram of the operation principle of the dual-frequency chirp coherent wind lidar in fig. 2.
Detailed Description
In order that those skilled in the art will better understand the disclosure, the invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The terms "first," "second," "third," "fourth," and the like in the description and claims of this application and in the above-described drawings are used for distinguishing between different objects and not for describing a particular order. Furthermore, the terms "comprising" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, article, or apparatus that comprises a list of steps or elements is not limited to only those steps or elements but may include other steps or elements not expressly listed.
Referring to fig. 1, fig. 1 is a block diagram of a dual-frequency chirp coherent wind lidar according to an embodiment of the present invention.
The dual-frequency chirp coherent wind lidar may include a light source module 101, a modulation light module 102, a transmitting and receiving module 103, a detection module 104, and a signal processing module 105.
The light source module 101 is configured to emit a dual-wavelength laser beam with a preset wavelength, center frequencies of the two laser beams are different, and a value of the wavelength may be selected according to a requirement of a user or an experimenter. The light source module can be a double-frequency laser source, and can also be two laser sources for emitting two beams of laser with different wavelengths.
In a specific embodiment, the laser source may be a dual frequency laser, a mode-locked laser, or a seed-injection semiconductor laser.
The modulation optical module 102 is configured to perform linear modulation on the dual-wavelength laser to emit a dual-frequency chirped continuous wave laser beam. The laser can adopt frequency modulation or phase modulation, and when the frequency modulation is carried out on the laser, the laser emits a dual-frequency linear frequency modulation continuous wave laser beam. Since frequency modulation is performed on the two beams with different center frequencies in time, the subsequent operation processing is simpler than phase modulation, and thus, it is preferable that the frequencies of the two beams be selectively modulated linearly. As the linear continuous wave has the advantages of no detection blind area, high distance resolution and the like for the detection target, the double-frequency linear frequency modulation continuous wave laser beam is selected as the coherent beam to detect the detection target.
Specifically, the modulation optical module 102 may include a modulator and a signal generator. The modulator is connected with the laser and used for linearly modulating the dual-wavelength laser, and the EOM modulator has good characteristics, so that the EOM modulator can be selected to linearly modulate the dual-wavelength laser, and of course, the modulator can be any other type of modulator. The signal generator is connected with the modulator and used for providing a modulation signal for the modulator, and the signal generator can be a triangular wave signal generator or a sawtooth wave signal generator, of course, other signal generators can be selected, such as a square wave signal generator.
Optionally, in some embodiments of this embodiment, the modulation optical module 102 may further include:
and the filter is connected with the modulator and is used for filtering background noise in the dual-frequency linear frequency modulation continuous wave laser beam. Because the stray light of the laser beam with the non-preset wavelength is inevitably mixed when the laser emits the laser beam, and all interference irrelevant to other useful signals is inevitably mixed in the system in the transmission process or the modulation process of the laser beam, the interference needs to be filtered out to obtain a relatively pure coherent beam, and the detection precision is favorably improved.
The filter can be a high-pass filter, a low-pass filter, a digital filter or a grating, and the specific type is adopted, so that the related technical personnel can select the filter according to the actual requirement, and the invention does not limit the filter at all.
In other embodiments of this embodiment, the method may further include:
and the laser amplifier can be connected with the filter and is used for amplifying the energy of the filtered double-frequency linear frequency modulation continuous wave laser beam. Since the laser beam is limited in some occasions (for example, due to nonlinear effects such as stimulated brillouin scattering), the power (energy) of the laser beam is small (low), which is unfavorable for subsequent operations and possibly affects the detection accuracy, and therefore, the power of the coherent beam needs to be amplified by the laser amplifier. The time resolution, the space resolution and the detection distance of the laser radar can be improved, and the detection precision can be improved.
It should be noted that if no filter is present in the system, the laser amplifier may be directly connected to the modulator.
The transmitting and receiving module 103 is configured to divide a dual-frequency linear frequency modulated continuous wave laser beam into a first laser beam and a second laser beam, where the first laser beam is incident to a detection target, and the second laser beam is used as a local oscillation light beam; and receiving an echo signal emitted by the detection target.
Specifically, the transceiver module 103 may include a first beam splitter, a circulator, an optical transceiver, and a second beam splitter.
The first beam splitter may be connected to the laser amplifier for splitting the dual frequency chirped continuous wave laser beam into two beams, a first laser beam and a second laser beam.
The beam splitter separates the two laser beams so that the two laser beams are transmitted according to preset light paths respectively. The beam splitter takes a first laser beam split by the dual-wavelength laser as a signal light beam to interact with a detection target and generate an echo signal, and takes a second laser beam as a local oscillation light beam to be coherent with the echo signal so as to obtain Doppler frequency shift information.
The beam splitter can be a light splitter, an optical fiber beam splitter, a polarization beam splitter, and the like, which type is specifically adopted, and a related technician can select the type according to actual requirements, and the invention does not limit the type.
The circulator is respectively connected with the optical transceiver, the first beam splitter and the second beam splitter and is used for enabling the first laser beam to be incident on the optical transceiver and enabling the second laser beam to be incident on the optical transceiver
A second beam splitter; and an echo signal scattered by the detection target is incident on the second beam splitter.
The circulator is mainly used to convert multiple signals, and other devices may be adopted as long as the circulator can function, which is not limited in this respect.
The optical transceiver is used for enabling the first laser beam to be incident on the detection target, receiving an echo signal emitted after interaction with the detection target and enabling the echo signal to be incident on the circulator.
The optical transceiver integrates transmission and reception, and may adopt a kc705 optical transceiver, an sfp optical transceiver, a graphic image optical transceiver, a communication protocol optical transceiver, an fmc daughter card optical transceiver or a dsp optical transceiver, and the like, which is specifically adopted, and a person skilled in the art can select the type according to actual needs, and the invention is not limited thereto.
The second beam splitter is used for enabling the echo signal and the second laser beam to be incident to the detection module.
It should be noted that, if there is no laser amplifier in the system, the first optical splitter may be connected to the filter; the first beam splitter may be connected directly to the modulator if no filter is present in the system.
Optionally, in some embodiments of this embodiment, for example, the method may further include:
and the attenuator is respectively connected with the first beam splitter and the second beam splitter and is used for attenuating the second laser beam, and the attenuated beam is used as the local oscillator light beam. The attenuator is used for attenuating the second laser beam (local oscillator light beam) through the attenuation process of the analog light beam in the atmosphere. Through attenuation processing of the local oscillator light beam, attenuation of the local oscillator light beam and attenuation of an echo signal in a transmission process are similar, coherence of two beams of light is facilitated, more accurate Doppler frequency shift information is obtained, and accordingly detection precision is improved.
In a preferred embodiment, the attenuator is a continuously adjustable attenuator. Of course, other types of attenuators can be used, and specifically, which type is used can be selected by the skilled person according to the actual requirement, and the present invention is not limited thereto.
It should be noted that, in the case of no attenuator, the second laser beam will be emitted to the second beam splitter via the first beam splitter; however, when an attenuator is provided, the second laser beam is transmitted to the attenuator through the first beam splitter, and is transmitted to the second beam splitter after being attenuated by the attenuator.
The detection module 104 is configured to perform optical beat frequency on the local oscillator light beam and the echo signal to obtain doppler shift information, and convert the optical signal into an electrical signal. A balanced detector may be included.
And the balance detector is connected with the second beam splitter and is used for carrying out optical beat frequency on the second laser beam and the echo signal so as to obtain a dual-frequency Doppler frequency shift signal. The second beam splitter makes the echo signal and the second laser beam incident to the balance detector, and after the echo signal and the second laser beam are mixed on a photosensitive surface of the detector, the double-frequency Doppler frequency shift values of the two beams of light can be respectively obtained by adopting an optical beat frequency mode. Of course, other detectors, such as photodetectors, may be employed.
The signal processing module 105 is configured to perform microwave beat frequency on the electrical signal to obtain doppler shift difference information, which includes analog-to-digital conversion, data acquisition, and data processing.
The signal processing module 105 may include:
an acquisition card and a data processing device.
The acquisition card is connected with the balance detector and is used for acquiring the dual-frequency Doppler frequency shift signal. In a preferred embodiment, the acquisition card may be an a/D acquisition card, but of course, other types of acquisition cards may be used, and the type may be selected by those skilled in the art according to actual needs.
And the data processing device is connected with the acquisition card and is used for performing microwave beat frequency on the electric signals to obtain a dual-frequency Doppler shift difference signal so as to invert the distance and speed information of the target.
The data processing apparatus may include:
DSP data processing unit and computer.
And the DSP data processing unit is used for performing microwave beat frequency on the electric signal converted from the second laser beam and the echo signal to obtain a Doppler frequency shift difference signal. Any error term simultaneously acting on the phases of two linear frequency modulation signals with different frequencies cannot influence the phase of a difference frequency signal obtained by microwave beat frequency, so that the problems of frequency sweep nonlinearity and distance velocity coupling are solved; for example, the traditional coherent laser radar detects wind speed by using the intermediate frequency signal, which is generally between 30MHz and 300MHz, and is just a band used by broadcasting stations and wireless communication devices, and the band has a wide coverage range and is densely used. Therefore, the use of the intermediate frequency signal makes the conventional coherent lidar susceptible to interference from the electromagnetic environment, and the electromagnetic signal radiated by the lidar during normal operation will also cause interference to other electronic devices. In the invention, for example, when the frequency spacing is 20GHz, the difference of Doppler frequency shift caused by wind speed of 30m/s is only 4000Hz, and the wave band is avoided, so that the invention has the characteristic of anti-electromagnetic interference.
In addition, the DSP data processing unit can also be used for realizing real-time processing and display of data, and is favorable for improving the use experience of a user.
And the calculation is used for inverting the distance and speed information of the target according to the Doppler frequency shift difference signal. For example, atmospheric aerosol is used as a detection object, and the laser radar system can be used for measuring atmospheric wind speed.
It should be noted that, in addition to calculating the distance and the speed of the detection target, other information about the detection target may be processed, such as imaging, temperature measurement, and the like.
By adding the calculation module, inversion and display can be carried out according to the acquired signals, and relevant information of the detected target can be output or obtained, so that the whole system has practical significance.
According to the technical scheme, the dual-wavelength linear frequency modulation laser is adopted, and the system structure and the signal processing part are simpler than those of the prior art; because the atmospheric turbulence has the same influence on the two frequency modulation beams, the influence of speckle noise caused by the unevenness of a detection target and the atmospheric turbulence effect is reduced; because linear continuous waves are adopted as coherent light beams, the distance resolution is high, and no blind area exists in the distance; in addition, the distance measurement and speed measurement can be simultaneously carried out on the detection target; the method further performs microwave beat frequency on the basis of optical beat frequency to obtain Doppler frequency shift difference information, and solves the problems of sweep frequency nonlinearity and distance velocity coupling; and is resistant to electromagnetic interference.
In order to better understand the idea and principle of the technical solution of the present application, the technical solution provided by the embodiments of the present invention is described in a specific application scenario below.
An electro-optical modulator with a modulation signal being a triangular wave signal is used for linearly modulating two continuous wave laser beams with different center frequencies (f1, f2) within time by adjusting the bandwidth B and the modulation frequency k, a dual-frequency linear frequency modulation coherent wind lidar structure shown in figure 3 is adopted, and distance measurement and speed measurement are carried out on an object by firstly optically beating frequency and extracting Doppler frequency shift difference information from microwave beating frequency. As shown in fig. 3, fd1 is the doppler shift value of the beam with center frequency f1, fd2 is the doppler shift value of the beam with center frequency f2, fm 1-f2 is the difference between the center frequencies of the two beams, fd1-fd2 is the difference between the doppler shifts of the two beams, and τ is the time delay between the local oscillation beam and the signal beam.
As shown in FIG. 3, the dual-frequency chirp coherent wind lidar may include a dual-frequency laser source 1, an EOM electro-optical modulator 2, a signal generator 3, a filter 4, a laser amplifier 5, a beam splitter 6, a circulator 7, an optical transceiver 8, a detection target 9, a continuously adjustable attenuator 10, a beam splitter 11, a balanced detector 12, an A/D acquisition card 13, a DSP data processing system 14, and a computer 15.
The connection relation of each device is as follows:
the output end of the double-frequency laser source 1 is connected with the input end of the EOM electro-optical modulator 2, the output end of the EOM electro-optical modulator 2 is connected with the input end of the filter 4, the control signal input end of the triangular wave signal generator 3 is connected with the control signal output end of the EOM electro-optical modulator 2, the output end of the filter 4 is connected with the input end of the laser amplifier 5, and the output end of the laser amplifier 5 is connected with the input end of the beam splitter 6; the beam splitter 6 divides the dual-frequency linear continuous wave laser into two beams, wherein the output of the port A is signal light, and the output of the port B is local oscillation light; the output end A of the beam splitter 6 is connected with the port A of the circulator 7, and the output end B of the beam splitter 6 is connected with the input end of the continuously adjustable attenuator 10; the port C of the circulator 7 is connected with the port A of the beam splitter 11; the port B of the circulator 7 is connected with an optical transceiver 8, a light beam emitted by the optical transceiver 8 irradiates on a detection target 9, a signal backscattered from the detection target 9 is collected by the optical transceiver 8, and then is transmitted to a beam splitter 11 through the end B and the end C of the circulator 7 in sequence; the output end of the continuously adjustable attenuator 10 is connected with the port B of the beam splitter 11, the local oscillation light and the signal light are mixed through the beam splitter 11 and then are connected to the balance detector 12, the output end of the balance detector 12 is connected with the input end of the A/D acquisition card 13, the output end of the A/D acquisition card 13 is connected with the input end of the DSP data processing system 14, and the output end of the DSP data processing system 14 is connected with the computer 15.
The principle of measuring distance and speed of a detected target is explained below, and f is introduced to simulate the frequency modulation nonlinearity under the actual simulation conditione(t) is a linear frequency deviation and hase(0)＝fe(T/2) ═ 0, where after a single-frequency signal is modulated, the frequency and phase of its swept band in a cycle are:
f1 +(t)＝f1+kt+fe(t)，
wherein k is B/(T/2) is 2B/T, and δRc/2B, B is MHz, the modulation bandwidth is determined by the range resolution, T is the modulation period (ms), phi1Is the initial phase.
The electric field of the dual-frequency chirped laser within one cycle may be:
E(t)＝E1(t)+E2(t) t∈(0，T)，
in the formula, E1And E2Is the amplitude phi1And phi2Is the phase angle.
The electric field for detecting the scattering signal of the target can be expressed as:
E'(t)＝E'1(t)+E'2(t) t∈(0，T)，
in the formula, E1`＝E1And the/alpha is the total loss of the reflected light, and when the signal light and the local oscillator light are subjected to frequency mixing detection on the photosurface of the balanced detector, the detector only responds to signals within a bandwidth range.
When T ∈ (τ, T/2), the light field illumination of the detector is:
wherein I ═ E1 2+E1，φ1 +＝2πf1τ，Δf1 +(t)＝kτ+fe(t)-fe(t-τ)＝Δf1+Δfe(t)。
If the doppler effect is considered and let τ vary with time, we can obtain:
similarly, there may be:
and also
The following can be obtained:
in the formula (f)d1＝2νf1/c，fd2＝2νf2V is the speed of the detection target, and c is the speed of light.
When T ∈ (T/2, T/2+ τ), the same can be said:
when T ∈ (T/2+ τ, T), similarly, there can be:
I1(t) and I2(t) can be acquired by an A/D acquisition card after being detected by a detector, the acquired signals are processed by DSP data signals and then are subjected to frequency mixing again, and the above formula is developed, wherein the items containing Doppler frequency shift information are as follows:
in the formula (I), the compound is shown in the specification,
in summary, the distance and speed of the detected object can be calculated as follows:
in the formula, when v is a positive value, the detection target is close to the laser radar; if the value is negative, the target is far away from the laser radar.
In the embodiment of the invention, the frequency of two continuous waves with different central frequencies is linearly modulated in time to obtain the dual-frequency linear frequency modulation laser, and the frequency modulation bandwidth B and the dual-frequency central frequency difference f of the dual-frequency linear frequency modulation lasermAre all much smaller than the center frequency f of the double frequency1And f2Therefore, the influence of the atmospheric turbulence on the two frequency-modulated lasers is almost the same, and the laser has the characteristic of insensitivity to the atmospheric turbulence. And the nonlinear frequency deviation f caused by the nonlinearity of the sweep frequencyeAnd (t) in the signal processing process, microwave beat frequency enables nonlinear frequency deviation terms to be mutually offset, and the obtained difference frequency signal does not contain the nonlinear frequency deviation terms.
In conclusion, the double-frequency linear frequency modulation coherent wind measurement laser radar not only realizes the simultaneous distance and speed measurement of the detection target, but also greatly reduces the influence of nonlinear frequency modulation and atmospheric turbulence effect on the speed measurement resolution, and has high detection precision, electromagnetic interference resistance and no distance blind area.
The embodiments are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same or similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
Those of skill would further appreciate that the various illustrative elements and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.
The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
The double-frequency linear frequency modulation coherent wind lidar provided by the invention is described in detail above. The principles and embodiments of the present invention are explained herein using specific examples, which are presented only to assist in understanding the method and its core concepts. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
Claims (7)
1. A dual-frequency chirp coherent wind lidar comprising:
the device comprises a light source module, a modulation optical module, a transmitting and receiving module, a detection module and a signal processing module;
the light source module is used for emitting a dual-wavelength laser beam with a preset wavelength;
the modulation optical module is used for carrying out linear modulation on the dual-wavelength laser beam to emit a dual-frequency linear frequency modulation continuous wave laser beam;
the transmitting and receiving module is used for dividing the dual-frequency linear frequency modulation continuous wave laser beam into a first laser beam and a second laser beam, the first laser beam is incident to a detection target, and the second laser beam is used as a local oscillation light beam; receiving the backscatter echo signal of the probe target;
the detection module is used for carrying out optical beat frequency on the local oscillator light beam and the echo signal so as to obtain Doppler frequency shift information and simultaneously converting an optical signal into an electric signal;
the signal processing module is used for performing microwave beat frequency on the electric signal to obtain Doppler frequency shift difference information;
the modulation optical module comprises a modulator and a signal generator; the modulator is used for carrying out linear frequency modulation on the dual-wavelength laser beam; the signal generator is connected with the modulator and used for providing a modulation signal for the modulator, and the signal generator is a triangular wave signal generator to generate triangular wave modulation information;
the signal processing module comprises an acquisition card and a data processing device; the acquisition card is connected with the balance detector and is used for acquiring signals; and the data processing device is connected with the acquisition card and is used for performing microwave beat frequency on the electric signal to obtain a dual-frequency Doppler frequency shift difference signal so as to invert the distance and speed information of the target and eliminate an error term generated by the nonlinear frequency modulation effect.
2. The dual-frequency chirp coherent wind lidar according to claim 1, wherein the modulating optical module further comprises:
and the filter is connected with the modulator and is used for filtering background noise in the dual-frequency linear frequency modulation continuous wave laser beam.
3. The dual frequency chirp coherent wind lidar of claim 2, wherein the modulating optical module further comprises:
and the laser amplifier is connected with the filter and used for amplifying the energy of the filtered double-frequency linear frequency modulation continuous wave laser beam.
4. The dual-frequency chirp coherent wind lidar according to claim 3, wherein the transmit receive module comprises:
the optical fiber coupling device comprises a first beam splitter, a second beam splitter, an optical transceiver and a circulator;
the first beam splitter is connected with the laser amplifier and is used for splitting the dual-frequency linear frequency modulation continuous wave laser beam into the first laser beam and the second laser beam;
the circulator is respectively connected with the optical transceiver, the first beam splitter and the second beam splitter and is used for enabling the first laser beam to be incident to the optical transceiver and enabling the second laser beam to be incident to the second beam splitter; and the echo signal is incident to the second beam splitter;
the optical transceiver is used for enabling the first laser beam to be incident on the detection target, receiving an echo signal scattered after interaction with the detection target and enabling the echo signal to be incident on the circulator;
the second beam splitter is used for enabling the echo signal and the second laser beam to be incident to the detection module.
5. The dual-frequency chirp coherent wind lidar of claim 4, wherein the detection module comprises the balanced detector, the balanced detector being coupled to the second beam splitter for optically beating the second laser beam and the echo signal to obtain a dual-frequency Doppler shift signal.
6. The dual-frequency chirp coherent wind lidar according to claim 4, wherein the transmit receive module further comprises:
and the attenuators are respectively connected with the first beam splitter and the second beam splitter and are used for attenuating the second laser beam, and the attenuated beam is used as the local oscillation light beam.
7. The dual-frequency chirp coherent wind lidar according to claim 6, wherein the data processing device comprises:
DSP data processing unit and computer.
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