Three-frequency molecular scattering Doppler laser radar system and detection method thereof

Abstract

The present invention relates to the field of Doppler laser radar technology, and specifically to a three-frequency molecular scattering Doppler laser radar system and a detection method thereof, wherein the emitted laser frequency alternates between , and , and the frequencies and are symmetrically located on both wings of the F-P interferometer transmission spectrum; the frequency is located near the peak of the F-P interferometer transmission spectrum. An F-P interferometer with a free spectrum spacing of 12 GHz and a spectrum width of 2 GHz serves as a frequency discriminator and a frequency locker. Its clear aperture is divided into two, and a two-way optical path is used in which the incident light passes through the F-P interferometer twice. The single-way transmission spectrum of the F-P interferometer is used to measure and lock the emitted laser frequency; the two-way transmission spectrum of the F-P interferometer is used to measure the wind field, temperature, and aerosol backscattering ratio. The present invention can realize simultaneous high-precision detection of the wind field, temperature, and aerosol backscattering ratio from near the ground to the lower stratosphere.

Description

Technical Field

[0001] The present invention relates to the technical field of Doppler laser radar, and in particular to a three-frequency molecular scattering Doppler laser radar system and a detection method thereof. Background Art

[0002] High-precision, high-temporal-resolution atmospheric wind data from near the surface to the lower stratosphere are closely related to human production and life, and are in urgent demand and widely used. Doppler lidar is currently one of the most effective tools for high-precision, high-temporal-resolution remote sensing of atmospheric wind fields. It can be divided into two types: coherent detection and direct detection. Direct detection can be further divided into edge detection and streak imaging. The actual detection accuracy and detection altitude of coherent detection Doppler lidar and direct detection Doppler lidar based on aerosol Mie scattering depend on the aerosol concentration in the atmosphere, and the detection altitude is generally limited to below 5 km. Traditional direct detection Doppler lidar based on Rayleigh scattering of atmospheric molecules is affected by interference from strong aerosol scattering signals in the lower layers, and the detection altitude is generally limited to above 5 km. Although the direct detection Doppler lidar based on atmospheric molecular Rayleigh scattering stripe imaging technology does not need to consider the influence of aerosol scattering signals, its detection sensitivity is very low and it is an energy distribution detection. It is greatly affected by the uneven energy of the output light spot and atmospheric turbulence. The actual detection accuracy and detection height cannot be guaranteed, and the requirements for the receiving optical path, detector and acquisition system are relatively high.

[0003] Real-time, high-precision, high-temporal-resolution wind data from the near-surface to the lower stratosphere is closely related to human production and life, and the demand for it is extremely urgent. It has important applications in improving climate models, advancing atmospheric thermodynamics and dynamics research, enhancing weather forecast accuracy, ensuring the safety of aircraft takeoff and landing, and improving wind energy utilization. Doppler lidar is currently one of the most effective tools for high-precision, high-temporal-resolution remote sensing of three-dimensional wind fields. Existing Doppler lidars are classified into two detection systems: coherent and direct. The technologies used in direct detection systems are further divided into fringe imaging and edge technology. Coherent detection Doppler lidar has high detection sensitivity and is currently widely used in wind farms, airports, and aviation. However, it requires narrow-linewidth pulsed laser technology and a diffraction-limited optical receiver. Furthermore, atmospheric turbulence disrupts laser coherence, limiting its effective detection range. Furthermore, due to the limitations of detection technology, these systems are only suitable for wind field observations in environments with a certain aerosol density. The advantage of streak imaging is that it does not require separation of aerosol and molecular scattering signals. When detecting aerosols, the narrow Mie scattering spectrum provides high detection sensitivity, and the influence of molecular scattering signals need not be considered. This offers certain advantages for measuring wind fields below the boundary layer. However, its disadvantage is that it requires energy distribution detection, placing high demands on the receiving optical path, detector, and signal acquisition system, and making wind speed inversion relatively complex. When detecting atmospheric molecules, the broad Rayleigh scattering spectrum results in low detection sensitivity. Given these disadvantages, it lacks advantages over edge technology. Currently, with the exception of GroundWinds, no other established systems employ streak imaging for molecular Doppler measurements. The advantage of edge technology is that it only detects the total energy of the signal, not its spatial distribution. This simplifies the detector and signal acquisition system requirements and simplifies data processing. It is the most commonly used technology in existing direct detection Doppler lidars, particularly molecular Rayleigh scattering Doppler lidars. However, its disadvantage is that it cannot directly measure wind speed using mixed signals from aerosol and molecular scattering.

[0004] Coherent detection Doppler lidar and direct detection Mie scattering Doppler lidar primarily detect aerosol particles in the atmosphere. They can generally only measure winds in the lower troposphere. Their detection accuracy is heavily dependent on aerosol concentration, and they cannot guarantee good accuracy and range under clear, lightly cloudy conditions. Direct detection Rayleigh scattering Doppler lidar based on edge technology primarily detects atmospheric molecules, where the aerosol scattering signal often acts as an interference signal. Due to strong interference from low-level clouds and aerosol scattering, they can generally only measure winds in the upper troposphere and above. Furthermore, because the spectral width of Rayleigh scattering from atmospheric molecules is temperature-dependent, the wind inversion process requires real-time atmospheric temperature. Consequently, due to factors such as the vertical distribution of aerosol concentration, uncertain atmospheric temperature, and mutual interference caused by aliasing of aerosol and molecular scattering signals, a single Doppler lidar cannot simultaneously and accurately measure winds at both high altitudes (above 8-10 km) and low altitudes (below 3-5 km). This makes it difficult to meet the practical application requirements of many fields. To measure both high- and low-altitude winds, researchers currently primarily employ hybrid systems or technologies. These employ different detection systems or technologies for both high- and low-altitude winds, combining the two receiving systems into a single, high- and low-altitude integrated Doppler lidar detection system. This results in a complex and costly system. Therefore, developing low-cost Doppler lidar technology capable of simultaneously and accurately detecting high and low altitude winds, particularly covering the entire troposphere and lower stratosphere, is of great significance.

[0005] The concentration of atmospheric molecules is relatively stable and largely unaffected by weather conditions. The spectral width of Rayleigh scattering by atmospheric molecules is proportional to the square root of the temperature. Therefore, given an accurate known atmospheric temperature profile, molecular scattering Doppler lidar can theoretically detect both high- and low-altitude wind fields. However, when detecting wind fields in the low-altitude atmosphere and in the mid- and high-altitude atmosphere where high-altitude clouds or volcanic ash are present, the wind speed measurements obtained by molecular scattering Doppler lidar will deviate significantly from the actual values ​​due to the strong interference of the aerosol Mie scattering signal. The density and pressure of the low-altitude atmosphere are so high that, in addition to aerosol Mie scattering and molecular Rayleigh elastic scattering, the intensity of Brillouin inelastic scattering by atmospheric molecules becomes non-negligible. Therefore, if molecular scattering Doppler lidar still uses the Rayleigh-Gaussian spectrum model when retrieving low-altitude wind fields, significant wind speed inversion errors will result. Therefore, for molecular scattering Doppler lidar to simultaneously measure high- and low-altitude wind fields with high precision, the following challenges must be addressed: obtaining real-time, high-precision atmospheric temperature profiles within the same detection area; reducing or eliminating the influence of aerosol Mie scattering interference signals; and developing a low-altitude atmospheric wind field inversion method based on a more accurate molecular scattering spectrum model. Based on these assumptions and to avoid the high process requirements of plating nanometer-scale precision steps on the FP interferometer substrate, a triple-frequency laser source and a single-channel FP interferometer are used instead of the single-frequency laser source and dual-channel FP interferometer used in traditional detection schemes. A double-pass optical path is constructed, in which the incident light passes through the FP interferometer twice. This results in a proposed triple-frequency molecular scattering Doppler lidar technology based on a single-channel, dual-pass FP interferometer. Research has revealed that no reported triple-frequency molecular scattering Doppler lidar technology based on a single-channel, dual-pass FP interferometer can accurately measure wind fields, temperature, and aerosol backscatter ratio from near the surface to the lower stratosphere. Summary of the Invention

[0006] The purpose of the present invention is to provide a three-frequency molecular scattering Doppler lidar system and a detection method thereof, which can be used to simultaneously detect atmospheric parameters such as wind field, temperature and aerosol backscatter ratio from near the ground to the lower stratosphere with high precision.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] Triple-frequency molecular scattering Doppler lidar system, including:

[0009] A seed light source, which is connected to a laser driving power supply and a controller;

[0010] an acousto-optic frequency shifter, the acousto-optic frequency shifter being connected to an acousto-optic frequency shifter driver;

[0011] The 355nm pulse laser is connected to the laser driving power supply, the controller and the trigger circuit respectively;

[0012] Furthermore, a 355nm pulsed laser is connected to a beam expander via a first beam splitter, the beam expander is connected to a light guide of a two-dimensional scanner via a first 45-degree reflector, and a glass plate is provided on the two-dimensional scanner;

[0013] The 2D scanner is connected to the Cassegrain telescope, which is connected to a second 1×2 fiber coupler via a 3-meter-long multimode fiber patch cable;

[0014] The second 1×2 fiber coupler is connected to the collimator, the collimator is connected to the narrow-band interference filter, and the narrow-band interference filter is connected to the second beam splitter;

[0015] The second beam splitter is connected to the first photomultiplier tube through a second convex lens;

[0016] The second beam splitter is also connected to the FP interferometer, and the FP interferometer is connected to the second photomultiplier tube through the third beam splitter and the third convex lens;

[0017] The third beam splitter is also connected to the second 45-degree reflector, the second 45-degree reflector is connected to the FP interferometer, and the FP interferometer is connected to the third photomultiplier tube through the third 45-degree reflector and the fourth convex lens;

[0018] The system uses an ultraviolet three-frequency laser source and a single-channel FP interferometer driven by an acousto-optic frequency shifter and an acousto-optic frequency shifter to control the emission laser frequency. At the same time, a two-way optical path is constructed in which the incident light passes through the FP interferometer twice to strongly suppress the interference of the Mie scattering signal. A three-Gaussian superposition model is used to describe the Rayleigh-Brillouin scattering spectrum of low-altitude atmospheric molecules, realizing the simultaneous detection of wind fields, temperature and aerosol backscattering ratio from near the ground to the lower stratosphere.

[0019] As a further solution of the present invention: the seed light source is connected to the acousto-optic frequency shifter, and the acousto-optic frequency shifter is connected to the 355nm pulse laser.

[0020] As a further solution of the present invention: the first beam splitter is connected to the first convex lens, the first convex lens is connected to the first 1×2 fiber coupler, and the first 1×2 fiber coupler is connected to a 1.5-meter-long multimode fiber jumper.

[0021] As a further solution of the present invention: the frequency of light coming out of the acousto-optic frequency shifter is 、 and The laser frequency is changed alternately Located near the peak frequency of the FP interferometer transmission spectrum.

[0022] As a further solution of the present invention: the free spectrum spacing of the FP interferometer is 12 GHz and the spectrum width is 2 GHz.

[0023] As a further solution of the present invention: the first photomultiplier tube, the second photomultiplier tube and the third photomultiplier tube are connected to the Licel transient recorder, and the three photomultiplier tubes are in both analog and photon counting working modes, and their output signals are collected by the Licel transient recorder.

[0024] A detection method for a three-frequency molecular scattering Doppler laser radar system, the method comprising the following steps:

[0025] The acousto-optic frequency shifter and the acousto-optic frequency shifter drive control the emission laser frequency to make its frequency 、 and Alternate between

[0026] A single-channel FP interferometer is used as the frequency discriminator and frequency locker, with its clear aperture divided into two and a round-trip double-pass optical path adopted;

[0027] The transmitted laser is reflected by the first beam splitter as a small part of the reference light. After passing through a 1.5-meter-long multimode fiber jumper, the fiber backscattered light with pulse width broadened is first collimated by the collimator and then incident on the FP interferometer. When the ratio of the signal received by the second photomultiplier tube and the first photomultiplier tube to the frequency of the emitted laser is The difference between the ratio of the signal received by the second photomultiplier tube and the first photomultiplier tube and 1 is measured and locked. and , and then Locked near the peak of the FP interferometer transmission spectrum;

[0028] Most of the emitted laser light passes through the first beam splitter, is expanded by a beam expander, guided by a first 45-degree reflector and a two-dimensional scanner, and then enters the atmospheric measured area in a specified direction. The atmospheric backscattered light is received by a Cassegrain telescope and, after being delayed by a 3-meter-long multimode fiber jumper, enters the receiving system in a time-series separated from the reference light.

[0029] The transmission frequency is and The transmittance of the molecular backscattered light containing Doppler shift information passing through the FP interferometer will increase and decrease by one time. When the third photomultiplier tube 27 receives the signal and emits the laser frequency The radial wind speed information is obtained by measuring the ratio of the signals received by the third photomultiplier tube.

[0030] As a further solution of the present invention: further comprising the following steps:

[0031] The generation of molecular Rayleigh scattering spectrum width and atmospheric temperature TThe broadening is proportional to the square root of T When the transmission frequency is and The sum of the transmittances of the molecular backscattered light signal passing through the FP interferometer in both directions will increase or decrease, and the emission frequency is The transmittance of the molecular backscattered light signal passing through the FP interferometer in two passes will decrease or increase. By measuring the frequency of the emitted laser and When the third photomultiplier tube receives the signal and the frequency of the emitted laser is The atmospheric temperature information is obtained by measuring the ratio of the signals received by the third photomultiplier tube.

[0032] As a further solution of the present invention: further comprising the following steps:

[0033] The transmission frequency is The transmittance of atmospheric aerosol and molecular backscattered light in two passes through the FP interferometer is very different. The aerosol backscattered light is almost completely suppressed. By measuring the frequency of the emitted laser The ratio of the signal received by the third photomultiplier tube to the signal received by the first photomultiplier tube can be used to obtain the aerosol backscattering ratio information.

[0034] As a further solution of the present invention: further comprising the following steps:

[0035] The laser emission frequency is 、 and When the light is emitted from the first photomultiplier tube and the second photomultiplier tube, the radial wind speed, temperature and aerosol backscatter ratio of the atmosphere are simultaneously inverted using a nonlinear iterative method.

[0036] Beneficial effects of the present invention:

[0037] (1) The hardware of the present invention uses an ultraviolet three-frequency laser source and a single-channel FP interferometer. At the same time, a two-way optical path is constructed in which the incident light passes through the FP interferometer twice to strongly suppress the interference of the Mie scattering signal. The three-Gaussian superposition model is used in the inversion algorithm to more accurately describe the Rayleigh-Brillouin scattering spectrum of low-altitude atmospheric molecules, which can achieve high-precision detection of wind field, temperature and aerosol backscattering ratio from near the ground to the lower stratosphere.

[0038] (2) The present invention adopts a triple-frequency laser and a single-channel FP interferometer to replace the single-frequency laser and dual-channel FP interferometer solution, which not only avoids the high requirement of plating nanometer-level precision steps on the FP interferometer substrate, but also reduces the difficulty and cost of system development, while simplifying the receiving system structure;

[0039] (3) The present invention utilizes the single-pass transmission spectrum of the FP interferometer to measure and lock the emission laser frequency, avoiding the need to add a separate FP interferometer locking channel and further simplifying the receiving system structure;

[0040] (4) The present invention solves the problem that the actual temperature and aerosol backscatter ratio are unknown in the traditional single-parameter wind speed measurement method, which may cause large wind speed inversion errors during the wind speed inversion process, thereby ensuring the accuracy of wind speed inversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0042] Figure 1 It is a structural block diagram of the three-frequency molecular scattering Doppler laser radar system of the present invention;

[0043] Figure 2 This is a schematic diagram of the wind field, temperature and aerosol backscatter ratio measurement principle of the present invention;

[0044] Figure 3 It is a single-pass and double-pass transmittance curve diagram of the aerosol and molecular backscattered light incident on the FP interferometer of the present invention.

[0045] Figure: 1. Seed light source, 2. Acousto-optic frequency shifter, 3. 355 nm pulsed laser, 4. First beam splitter, 5. Beam expander, 6. First 45-degree reflector, 7. Two-dimensional scanner, 8. Glass plate, 9. Cassegrain telescope, 10. 3-meter multimode fiber patch cord, 11. First convex lens, 12. First 1×2 fiber coupler, 13. 1.5-meter multimode fiber patch cord, 14. Second 1×2 fiber coupler, 15. Collimator, 16. Narrowband interference filter, 17. Second beam splitter, 18. Second convex lens, 19. First photomultiplier tube, 20. FP interferometer, 21. Third beam splitter, 22. Third convex lens, 23. Second photomultiplier tube, 24. Second 45-degree reflector, 25. Third 45-degree reflector, 26. Fourth convex lens, 27. Third photomultiplier tube, 28. Licel transient recorder, 29. Trigger circuit, 30. FP interferometer controller, 31. Two-dimensional scanner controller, 32. Laser driver power supply and controller, 33. Acousto-optic frequency shifter driver, 34. Industrial computer. DETAILED DESCRIPTION

[0046] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0047] Example 1

[0048] like Figure 1 As shown, the triple-frequency molecular scattering Doppler laser radar system provided by the embodiment of the present invention includes:

[0049] The seed light source 1 is connected to the laser driving power supply and the controller 32;

[0050] The acousto-optic frequency shifter 2 is connected to the acousto-optic frequency shifter driver 33; the acousto-optic frequency shifter driver 33 controls the frequency of light coming out of the acousto-optic frequency shifter. 、 and alternating between is the laser emission frequency, and The frequency is The emission frequency of the emitted laser after passing through the acousto-optic frequency shifter;

[0051] 355nm pulse laser 3, 355nm pulse laser 3 are connected to the laser driving power supply and controller 32 and trigger circuit 29 respectively;

[0052] And, the seed light source 1 is connected to the acousto-optic frequency shifter 2, and the acousto-optic frequency shifter 2 is connected to the 355nm pulse laser 3;

[0053] The 355nm pulse laser 3 is connected to the first beam splitter 4, the first beam splitter 4 is connected to the beam expander 5, the beam expander 5 is connected to the first 45-degree reflector 6, the first 45-degree reflector 6 is connected to the two-dimensional scanner 7 for light guidance, and a glass plate 8 is provided on the two-dimensional scanner 7;

[0054] The first beam splitter 4 is connected to the first convex lens 11, the first convex lens 11 is connected to the first 1×2 fiber coupler 12, and the first 1×2 fiber coupler is connected to a 1.5-meter-long multimode fiber jumper 13;

[0055] The two-dimensional scanner 7 is connected to the Cassegrain telescope 9, and the Cassegrain telescope 9 is connected to the second 1×2 fiber coupler 14 via a 3-meter-long multimode fiber jumper;

[0056] The second 1×2 fiber coupler 14 is connected to the collimator 15, the collimator 15 is connected to the narrow-band interference filter 16, and the narrow-band interference filter 16 is connected to the second beam splitter 17;

[0057] The second beam splitter 17 is connected to the second convex lens 18, and the second convex lens 18 is connected to the first photomultiplier tube 19;

[0058] The second beam splitter 17 is also connected to the FP interferometer 20, the FP interferometer 20 is connected to the third beam splitter 21, the third beam splitter 21 is connected to the third convex lens 22, and the third convex lens 22 is connected to the second photomultiplier tube 23;

[0059] The third beam splitter 21 is also connected to the second 45-degree reflector 24, the second 45-degree reflector 24 is connected to the FP interferometer 20, the FP interferometer 20 is connected to the third 45-degree reflector 25, the third 45-degree reflector 25 is connected to the fourth convex lens 26, and the fourth convex lens 26 is connected to the third photomultiplier tube 27;

[0060] Furthermore, the Licel transient recorder 28 is connected to the trigger circuit 29 , the FP interferometer 20 is connected to the FP interferometer controller 30 , and the two-dimensional scanner 7 is connected to the two-dimensional scanner controller 31 .

[0061] The trigger circuit 29 , the FP interferometer controller 30 , the two-dimensional scanner controller 31 , the laser driving power supply and controller 32 , and the acousto-optic frequency shifter driver 33 are all connected to the industrial computer 34 and are uniformly controlled by the industrial computer 34 .

[0062] The specific working process of the Doppler laser radar system of the present invention is as follows: the seed light source 1 is connected to the laser driving power supply and the controller 32, the acousto-optic frequency shifter 2 is connected to the acousto-optic frequency shifter driver 33, and the driving signal controls the light frequency coming out of the acousto-optic frequency shifter 2 to be in the range of 0.1-1.0. 、 and The laser frequency is changed alternately Located near the peak frequency of the transmission spectrum of FP interferometer 20, 355nm pulsed laser 3 is connected to the laser driver and controller 32, and trigger circuit 29. The seed light emitted by seed light source 1 is frequency-shifted by acousto-optic frequency shifter 2 and then injected into 355nm pulsed laser 3, emitting narrow-linewidth pulsed laser light.

[0063] The transmitted laser is split into two beams by a first beam splitter 4. The transmitted beam, which accounts for the majority of the energy, is expanded by a beam expander 5, guided by a first 45-degree reflector 6 and a two-dimensional scanner 7, and ultimately passes perpendicularly through a glass plate 8 at a preset angle into the atmospheric region being measured. The atmospheric backscattered light is received by a Cassegrain telescope 9 and coupled into a 3-meter-long multimode fiber optic patch cable 10.

[0064] The receiving end of the fiber optic patch cord 10 is located at the focal point of the Cassegrain telescope 9. The other end of the fiber optic patch cord 10 is connected to one branch of a second 1×2 fiber coupler 14. The reflected beam from the first beam splitter 4 serves as reference light for measuring and locking the transmitted laser frequency. This light is coupled by a first convex lens 11 into one branch of a first 1×2 fiber coupler 12. The combining end of the first 1×2 fiber coupler 12 is connected to a 1.5-meter-long multimode fiber patch cord 13. After passing through the 1.5-meter-long multimode fiber patch cord 13, the reference light is time-broadened to quasi-continuous-wave backscattered light, which is output from the other branch of the first 1×2 fiber coupler 12 and connected to the other branch of the second 1×2 fiber coupler 14. The reference light and atmospheric backscattered light signals are time-shared and enter the combining end of the second 1×2 fiber coupler 14. The fiber end face of the combining end of the second 1×2 fiber coupler 14 is located at the object focus of the collimator 15. The outgoing light beam from the combined end of the second 1×2 fiber coupler 14 is collimated by a collimator 15 , filtered by a narrow-band interference filter 16 , and then split into two beams by a second beam splitter 17 .

[0065] The reflected light beam is converged by the second convex lens 18 onto the photosensitive surface of the first photomultiplier tube 19; the transmitted light beam is incident normally onto the FP interferometer 20. The light beam that passes through the FP interferometer 20 is split into two beams by the third beam splitter 21. The transmitted light beam is converged by the third convex lens 22 onto the photosensitive surface of the second photomultiplier tube 23; the reflected light beam is reflected again by the second 45-degree reflector 24 and then incident normally on the FP interferometer 20. The light beam that passes through the FP interferometer 20 again is converged by the third 45-degree reflector 25 and the fourth convex lens 26 and is incident on the photosensitive surface of the third photomultiplier tube 27.

[0066] The FP interferometer 20 has a free spectrum spacing of 12 GHz and a spectral width of 2 GHz. These design parameters, including the free spectrum spacing, spectral width, and the frequency spacing between the three emitted lasers, allow for the measurement of both high- and low-level wind fields, temperature, and aerosol backscatter ratio. The first, second, and third photomultiplier tubes 19, 23, and 27 are connected to a Licel transient recorder 28. These three photomultiplier tubes operate in both analog and photon counting modes, with their output signals collected by the Licel transient recorder 28. The Licel transient recorder 28 is connected to a trigger circuit 29, an FP interferometer controller 30 is connected to the FP interferometer 20, and a two-dimensional scanner controller 31 is connected to the two-dimensional scanner 7. The trigger circuit 29, FP interferometer controller 30, two-dimensional scanner controller 31, laser driver power supply and controller 32, and acousto-optic frequency shifter driver 33 are connected to an industrial computer 34 and are controlled by the industrial computer 34.

[0067] Example 2

[0068] like Figure 2and Figure 3 As shown, the detection method of the three-frequency molecular scattering Doppler laser radar system provided by the embodiment of the present invention includes the following steps:

[0069] The acousto-optic frequency shifter 2 and the acousto-optic frequency shifter driver 33 control the frequency of the emitted laser so that its frequency is between 、 and Alternate between

[0070] A single-channel FP interferometer 20 is used as a frequency discriminator and frequency locker. Its clear aperture is divided into two, and a round-trip double-pass optical path is used. The single-pass transmission spectrum of the FP interferometer 20 is used to measure and lock the frequency of the emitted laser; the double-pass transmission spectrum of the FP interferometer 20 is used to measure the wind field, temperature and aerosol backscattering ratio. A small part of the emitted laser is reflected by the first beam splitter 4 as a reference light. After passing through a 1.5-meter-long multimode fiber jumper 13, the fiber backscattered light with a widened pulse width is first collimated by the collimator 15 and then incident on the FP interferometer 20. The frequency of the emitted laser is 1.5 meters. When the ratio of the signal received by the second photomultiplier tube 23 and the first photomultiplier tube 19 to the frequency of the emitted laser is The difference between the ratio of the signal received by the second photomultiplier tube 23 and the first photomultiplier tube 19 and 1 is measured and locked. and , and then Locking near the peak of the transmission spectrum of the FP interferometer 20;

[0071] After passing through the first beam splitter 4, the majority of the emitted laser light is expanded by the beam expander 5, guided by the first 45-degree reflector 6 and the two-dimensional scanner 7, and then enters the atmospheric measurement area in the specified direction. The atmospheric backscattered light is received by the Cassegrain telescope 9 and, after being delayed by a 3-meter-long multimode fiber optic patch cable 10, is separated from the reference light in time and enters the receiving system.

[0072] The transmission frequency is and The transmittance of the molecular backscattered light containing Doppler shift information passing through the FP interferometer 20 will increase and decrease respectively. When the third photomultiplier tube 27 receives the signal and emits the laser frequency The radial wind speed information can be obtained by the ratio of the signals received by the third photomultiplier tube 27;

[0073] The generation of molecular Rayleigh scattering spectrum width and atmospheric temperature T The broadening is proportional to the square root of T When the transmission frequency is and The sum of the transmittances of the molecular backscattered light signal passing through the FP interferometer 20 in both directions will increase or decrease, and the emission frequency The transmittance of the molecular backscattered light signal passing through the FP interferometer 20 in two passes will decrease or increase. and When the third photomultiplier tube 27 receives the signal and the frequency of the emitted laser is The ratio of the signals received by the third photomultiplier tube 27 can be used to obtain atmospheric temperature information;

[0074] The transmission frequency is The transmittance of atmospheric aerosol and molecular backscattered light in two passes through FP interferometer 20 is very different. The aerosol backscattered light is almost completely suppressed. By measuring the emission laser frequency The aerosol backscatter ratio information can be obtained by calculating the ratio of the signal received by the third photomultiplier tube 27 to the signal received by the first photomultiplier tube 19.

[0075] The laser emission frequency is 、 and When the receiving signals of the two photomultiplier tubes 27 and 19 are inverted, the atmospheric radial wind speed, temperature and aerosol backscattering ratio can be obtained simultaneously by using a nonlinear iterative method.

[0076] During operation, the two-dimensional scanner 7 can use three-beam, four-beam, etc. scanning modes within a detection cycle. After obtaining radial wind speeds in multiple measurement directions, vector synthesis can be performed to obtain the magnitude and direction of the vector wind speed.

[0077] More specifically, the process of simultaneously inverting the atmospheric radial wind speed, temperature, and aerosol backscatter ratio using a nonlinear iterative method is as follows:

[0078] The total divergence angle is , the frequency is The transmittance of monochromatic light incident on the FP interferometer is:

[0079]

[0080] Where: is the average transmittance of the FP interferometer, is the effective reflectivity of the FP interferometer plate, and are the peak transmittance and free spectrum spacing of the FP interferometer, respectively, and n is the natural order number.

[0081] Assuming that the emitted laser is a Gaussian spectrum line, the emitted laser or aerosol backscattering spectrum can be expressed as:

[0082]

[0083] Where: , is the laser emission spectrum width; is the center frequency of the backscatter spectrum, is the center frequency of the emitted laser, is the Doppler frequency, is the radial wind speed, is the independent variable, representing the laser frequency. However, the backscattering spectrum of atmospheric molecules is no longer a single Gaussian type, especially when detecting the low-altitude atmosphere, the influence of Brillouin scattering needs to be considered. At present, it is generally believed that the Tenti S6 numerical model is the most accurate model to describe the Rayleigh-Brillouin scattering spectrum of low-altitude atmospheric molecules, but because it is very complex and there is no simple analytical expression, it is not convenient for practical application. The present invention adopts the three-Gaussian superposition analytical model proposed by B. Witschas to describe the backscattering spectrum of atmospheric molecules, that is:

[0084]

[0085] Where: , P is the atmospheric pressure, is the shear viscosity; C , , , Both y The analytical function of y Obtain:

[0086]

[0087]

[0088]

[0089]

[0090] Where: is the width of the Rayleigh scattering line at 1 / e height, is the laser wavelength, k is the Boltzmann constant, T is the atmospheric temperature, M is the molecular mass.

[0091] The single-pass transmittance of the emitted laser or aerosol backscattered light incident on the FP interferometer is

[0092]

[0093] in:

[0094]

[0095] The single-pass transmittance of the backscattered light of atmospheric molecules incident on the FP interferometer is

[0096]

[0097] in:

[0098]

[0099]

[0100] The two-way transmittance of the emitted laser or aerosol backscattered light incident on the FP interferometer is

[0101]

[0102] in:

[0103]

[0104] The two-way transmittance of the backscattered light of atmospheric molecules incident on the FP interferometer is

[0105]

[0106] in:

[0107]

[0108]

[0109] Set the FP interferometer parameters and set y =0.20 ( P =0.47×10 5 Pa, T =249K) and y =0.32 ( P =0.80×10 5 Pa, T =275K), the single-pass and double-pass transmittances of aerosol and molecular backscattered light incident on the FP interferometer are obtained by simulation as follows Figure 3 As shown. Figure 1 As shown, when the frequency is ( or Before the laser emission enters the atmosphere, a small portion is separated as reference light and directly enters the receiving system. The number of photoelectrons received by the second photomultiplier tube that receives the one-way FP interferometer signal and the first photomultiplier tube used for energy monitoring is:

[0110]

[0111]

[0112] From this we can get

[0113]

[0114] Where: , is the system calibration constant; at the same time, , ,in is the frequency difference value set by the frequency shifter. It can be determined by system calibration, so the emission laser frequency can be inverted according to the above formula 、 and .

[0115] When the frequency is ( 、 and ) laser is emitted along a certain radial direction, and the backscattered light enters the receiving system, the third photomultiplier tube that receives the double-pass FP interferometer signal, and the first photomultiplier tube for energy monitoring receives the height z The number of atmospheric backscattered photoelectrons at is:

[0116]

[0117]

[0118] Where: Calibrate constants for the system; , is the Doppler frequency shift; for z Aerosol backscatter ratio at altitude, and are the vertical heights received by the laser radar z ~ z + The number of backscattered photoelectrons between molecules and aerosols, is the vertical distance resolution. Then the effective transmittance function of the double-pass FP interferometer is:

[0119]

[0120] After analysis, the wind speed response function is defined , temperature response function and aerosol backscatter ratio response function They are (omit the variables in the function) z )

[0121]

[0122]

[0123]

[0124] Where: , , can be accurately determined by the average value of the first 10 bin signals (with a large signal-to-noise ratio) received by the energy monitoring detector E, that is,

[0125]

[0126] The corresponding wind speed, temperature and aerosol backscatter ratio measurement sensitivities are

[0127]

[0128]

[0129]

[0130] Where: Atmospheric pressure P Using the atmospheric model, the above simultaneous equations defining wind speed, temperature and aerosol backscattering ratio response function are obtained.

[0131]

[0132] The linearization of the above equation yields the iterative equation:

[0133]

[0134] in: j =1, 2, 3… 、 and express 、 T and No. j Iteration value; , , ; , , ; and Respectively Temperature measurement sensitivity and aerosol backscatter ratio measurement sensitivity; and Respectively Wind speed measurement sensitivity and aerosol backscatter ratio measurement sensitivity; and Respectively Wind speed measurement sensitivity and temperature measurement sensitivity.

[0135] Set the initial radial wind speed ,temperature and aerosol backscatter ratio , and set the iteration termination condition 、 and in 、 and After multiple iterations, accurate inversion can be obtained simultaneously. 、 T and .

[0136] According to the error transfer formula, we can get 、 T and The measurement errors are:

[0137]

[0138]

[0139]

[0140] Where: 、 and Wind speed response functions , temperature response function and aerosol backscatter ratio response function The measurement signal-to-noise ratio is

[0141]

[0142]

[0143] .

[0144] in: 、 and The third photomultiplier tube that receives the double-pass FP interferometer signal receives the height z The laser emission frequency at 、 and The number of atmospheric backscattered photoelectrons; The first photomultiplier tube for energy monitoring receives the height z The laser emission frequency at The number of atmospheric backscattered photoelectrons.

[0145] The above is a detailed description of an embodiment of the present invention. However, the content described is only a preferred embodiment of the present invention and should not be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A three-frequency molecular scattering Doppler laser radar system, characterized in that: include: A seed light source (1), the seed light source (1) is connected to a laser driving power supply and a controller (32); an acousto-optic frequency shifter (2), the acousto-optic frequency shifter (2) being connected to an acousto-optic frequency shifter driver (33); A 355nm pulse laser (3), wherein the 355nm pulse laser (3) is connected to a laser driving power supply and controller (32) and a trigger circuit (29); Furthermore, the 355 nm pulsed laser (3) is connected to the beam expander (5) via the first beam splitter (4), the beam expander (5) is connected to the two-dimensional scanner (7) via the first 45-degree reflector (6), and a glass plate (8) is provided on the two-dimensional scanner (7); The two-dimensional scanner (7) is connected to the Cassegrain telescope (9), and the Cassegrain telescope (9) is connected to the second 1×2 fiber coupler (14) via a 3-meter-long multimode fiber jumper; The second 1×2 fiber coupler (14) is connected to the collimator (15), the collimator (15) is connected to the narrow-band interference filter (16), and the narrow-band interference filter (16) is connected to the second beam splitter (17); The second beam splitter (17) is connected to the first photomultiplier tube (19) via a second convex lens (18); The second beam splitter (17) is also connected to the FP interferometer (20), and the FP interferometer (20) is connected to the second photomultiplier tube (23) through the third beam splitter (21) and the third convex lens (22); The third beam splitter (21) is also connected to the second 45-degree reflector (24), the second 45-degree reflector (24) is connected to the FP interferometer (20), and the FP interferometer (20) is connected to the third photomultiplier tube (27) through the third 45-degree reflector (25) and the fourth convex lens (26); The system uses an ultraviolet three-frequency laser source and a single-channel FP interferometer (20) whose emission laser frequency is controlled by an acousto-optic frequency shifter (2) and an acousto-optic frequency shifter driver (33). At the same time, a double-pass optical path is constructed in which the incident light passes through the FP interferometer (20) twice to strongly suppress the interference of the Mie scattering signal. A three-Gaussian superposition model is used to describe the Rayleigh-Brillouin scattering spectrum of low-altitude atmospheric molecules, thereby realizing the simultaneous detection of wind field, temperature and aerosol backscattering ratio from near the ground to the lower stratosphere. The frequency of light coming out of the acousto-optic frequency shifter (2) is 、 and The laser frequency is changed alternately Located near the peak frequency of the transmission spectrum of the FP interferometer (20); The free spectrum spacing of the FP interferometer (20) is 12 GHz and the spectrum width is 2 GHz; The reflected light beam is converged by the second convex lens (18) to the photosensitive surface of the first photomultiplier tube (19); the transmitted light beam is incident on the FP interferometer (20), and the light beam passing through the FP interferometer (20) is split into two beams by the third beam splitter (21); the transmitted light beam is converged by the third convex lens (22) to the photosensitive surface of the second photomultiplier tube (23); the reflected light beam is reflected again by the second 45-degree reflector (24), and then is incident on the FP interferometer (20) in the reverse direction, and the light beam passing through the FP interferometer (20) again is converged by the third 45-degree reflector light guide (25) and the fourth convex lens (26), and is incident on the photosensitive surface of the third photomultiplier tube (27).

2. The triple-frequency molecular scattering Doppler laser radar system according to claim 1, characterized in that: The seed light source (1) is connected to the acousto-optic frequency shifter (2), and the acousto-optic frequency shifter (2) is connected to the 355nm pulse laser (3).

3. The triple-frequency molecular scattering Doppler laser radar system according to claim 2, characterized in that: The first beam splitter (4) is connected to the first convex lens (11), the first convex lens (11) is connected to the first 1×2 optical fiber coupler (12), and the first 1×2 optical fiber coupler is connected to a 1.5-meter-long multimode optical fiber jumper (13).

4. The triple-frequency molecular scattering Doppler laser radar system according to claim 1, characterized in that: The first photomultiplier tube (19), the second photomultiplier tube (23) and the third photomultiplier tube (27) are connected to a Licel transient recorder (28). The three photomultiplier tubes are simultaneously in two working modes: analog and photon counting. The output signals of the three photomultiplier tubes are collected by the Licel transient recorder (28).

5. A detection method for a triple-frequency molecular scattering Doppler laser radar system according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: The acousto-optic frequency shifter (2) and the acousto-optic frequency shifter driver (33) control the frequency of the emitted laser so that its frequency is 、 and Alternate between A single-channel FP interferometer (20) is used as a frequency discriminator and frequency locker, its clear aperture is divided into two, and a round-trip double-pass optical path is adopted; A small portion of the emitted laser is reflected by the first beam splitter (4) as reference light. After passing through a 1.5-meter-long multimode fiber jumper (13), the fiber backscattered light with pulse width broadened is first collimated by the collimator (15) and then incident on the FP interferometer (20). When the ratio of the received signal of the second photomultiplier tube (23) and the first photomultiplier tube (19) to the emitted laser frequency is The difference between the ratio of the signal received by the second photomultiplier tube (23) and the first photomultiplier tube (19) and 1 is measured and locked. and , and then Locked near the peak of the transmission spectrum of the FP interferometer (20); Most of the emitted laser light passes through the first beam splitter (4), is expanded by the beam expander (5), guided by the first 45-degree reflector (6) and the two-dimensional scanner (7), and then enters the atmospheric measured area in a specified direction; the atmospheric backscattered light is received by the Cassegrain telescope (9), and after being delayed by a 3-meter-long multimode optical fiber jumper (10), it enters the receiving system in a time sequence separated from the reference light; The transmission frequency is and The transmittance of the molecular backscattered light containing Doppler shift information passing through the FP interferometer (20) will increase and decrease respectively. When the third photomultiplier tube (27) receives the signal and emits the laser frequency The radial wind speed information is obtained by measuring the ratio of the signals received by the third photomultiplier tube (27).

6. The detection method of the triple-frequency molecular scattering Doppler laser radar system according to claim 5, characterized in that: The following steps are also included: The generation of molecular Rayleigh scattering spectrum width and atmospheric temperature T The broadening is proportional to the square root of T When the transmission frequency is and The sum of the transmittances of the molecular backscattered light signal passing through the FP interferometer (20) in two passes will increase or decrease, and the emission frequency is The transmittance of the molecular backscattered light signal will decrease or increase after passing through the FP interferometer (20) in two passes. and When the third photomultiplier tube (27) receives the signal and the frequency of the emitted laser is The atmospheric temperature information is obtained by measuring the ratio of the signals received by the third photomultiplier tube (27).

7. The detection method of the triple-frequency molecular scattering Doppler laser radar system according to claim 6, characterized in that: The following steps are also included: The transmission frequency is The transmittance of atmospheric aerosol and molecular backscattered light in two passes through the FP interferometer (20) is very different, and the aerosol backscattered light is almost completely suppressed. The aerosol backscatter ratio information is obtained by calculating the ratio of the signal received by the third photomultiplier tube (27) to the signal received by the first photomultiplier tube (19).

8. The detection method of the triple-frequency molecular scattering Doppler laser radar system according to claim 7, characterized in that: The following steps are also included: The laser emission frequency is 、 and When , the receiving signals of the two third photomultiplier tubes (27) and the first photomultiplier tube (19) are simultaneously inverted using a nonlinear iterative method to obtain the atmospheric radial wind speed, temperature and aerosol backscattering ratio.

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