CN113281774B - Efficient and compact high-spectral-resolution laser radar system and acquisition method of aerosol backscattering coefficient and extinction coefficient - Google Patents
Efficient and compact high-spectral-resolution laser radar system and acquisition method of aerosol backscattering coefficient and extinction coefficient Download PDFInfo
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- 238000005086 pumping Methods 0.000 claims abstract description 8
- 238000012545 processing Methods 0.000 claims abstract description 6
- 230000003595 spectral effect Effects 0.000 claims description 16
- PNDPGZBMCMUPRI-UHFFFAOYSA-N iodine Chemical compound II PNDPGZBMCMUPRI-UHFFFAOYSA-N 0.000 claims description 14
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- 241000209094 Oryza Species 0.000 description 2
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- G01S17/88—Lidar systems specially adapted for specific applications
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
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- G01S7/481—Constructional features, e.g. arrangements of optical elements
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- G—PHYSICS
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- 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
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
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Abstract
The invention discloses a high-efficiency compact high-spectral-resolution laser radar system, which comprises three modules: the device comprises a laser emitting module, a signal receiving module and a signal acquisition processing module. The laser emission module is an all-solid-state frequency-locking pulse laser based on diode pumping, the laser adopts a frequency locking technology to realize single-frequency pulse laser output, and then a Galileo beam expansion lens is used for compressing the divergence angle of emergent laser to obtain a farther detection distance; the signal receiving module consists of a telescope, a small aperture diaphragm, a collimating lens, a narrow-band filter, an etalon, a vibrating mirror, an absorption cell, a polarization beam splitter, a focusing lens, a photomultiplier and the like. The system of the invention realizes compact design of the system while further improving the receiving efficiency.
Description
Technical Field
The invention belongs to the field of laser radars, and particularly relates to a high-efficiency compact high-spectral-resolution laser radar system for environmental monitoring and a corresponding acquisition method of an aerosol backscattering coefficient and an extinction coefficient.
Background
The back scattering signal component generated by the interaction of the laser radar pulse in the atmosphere comprises atmospheric gas molecules and aerosol particles, the generated scattered light is relatively weak due to the small molecular size, the Rayleigh scattering cross section is inversely proportional to the fourth power of the excitation wavelength, and the scattered light of the laser is scattered by the aerosol particles. For a particular wavelength of a certain lidar, molecular scattering varies directly with the concentration of atmospheric molecules, but aerosol scattering is complex, depending on the particle size distribution and the refractive index of the aerosol particles. These aerosol particles vary significantly with region and time, so they cannot be estimated and predicted accurately. The molecular scattering can be estimated relatively accurately, and can be obtained only through standard atmospheric information or atmospheric temperature and pressure distribution data above an observation point. Therefore, the laser radar equation contains two variables of an extinction coefficient and a backscattering coefficient determined by aerosol, namely, one equation is to invert two unknowns, and a general Mit laser radar has theoretical defects.
The university of south Beijing information engineering Bo Lingbing proposes a high spectral Resolution Lidar (HIGH SPECTRAL Resolution Lidar, HSRL) system in CN204631247U that solves the difficulty of inverting two unknown amounts of aerosol scattering coefficient and extinction coefficient using one radar equation encountered by conventional back-scattered Lidar by locking the lasing frequency, and by separating the aerosol scattering component from the molecular scattering component by a fabry-perot interference narrowband spectral filter. The high-spectrum-resolution laser radar uses single-frequency laser as a detection light source, and the received atmospheric scattering spectrum consists of aerosol meter scattering and molecular Rayleigh scattering. The spectral width of the aerosol meter scattering is negligible, while the spectrum of the molecular rayleigh scattering is wider, for example, when 532nm single-frequency laser detection is adopted, the meter scattering spectral width is equivalent to the line width of the emitted laser (< 100 MHz), and the full width at half maximum of the rayleigh scattering is about 2.5GHz. Based on the difference of the two scattering characteristics, the two scattering characteristics can be separated by utilizing a narrow-band optical filter, and molecular scattering and aerosol scattering can be respectively measured on the basis, so that the backscattering coefficient and extinction coefficient of aerosol can be directly obtained through inversion, and the theoretical defect of the Mie scattering laser radar is overcome.
However, the existing high-spectrum resolution laser radar has large volume and weight, and because the devices such as a light source and a frequency discriminator in the existing scheme are greatly affected by temperature, humidity, vibration and the like, namely the system stability is poor. The invention aims to provide a high-spectral-resolution laser radar system, which is used in combination with a vibrating mirror switching receiving channel in a receiving system, so that the receiving efficiency is further improved, meanwhile, the compact design of the system is realized, in addition, the laser radar system is less influenced by the working environment, the engineering application can be realized, and the whole system is more stable and reliable.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a high-spectrum-resolution laser radar system, which is used in combination with a vibrating mirror switching receiving channel in a receiving system, so that the receiving efficiency is further improved, meanwhile, the compact design of the system is realized, in addition, the laser radar system is less influenced by the working environment, the engineering application can be realized, and the whole system is more stable and reliable.
The technical scheme is as follows: the invention discloses a high-efficiency compact high-spectral resolution laser radar system, which comprises a laser, a reflecting mirror, a window mirror, a telescope, a small aperture diaphragm, a collimating mirror, an optical filter, an etalon, a galvanometer, a polarizing beam splitter, a silver-plated reflecting mirror, a focusing mirror, an iodine molecule absorption tank and a photomultiplier, wherein laser emitted by the laser is reflected and transmitted through the reflecting mirror and the emergent direction of the laser is controlled; the laser emission and the signal receiving are carried out through the same window mirror; the laser further passes through a telescope and a small aperture diaphragm, and then the received signals are collimated by a collimating lens; the collimated signals are emitted into the vibrating mirror after passing through the optical filter and the etalon, the optical filter and the etalon are used for inhibiting background light noise, and the rotation directions of the vibrating mirror are two: a polarization channel and a hyperspectral channel;
Polarization channel: the echo signals are divided into horizontal polarized signals and vertical polarized signals by a polarization beam splitter, and the horizontal polarized signals are converged to a first photomultiplier by a first focusing mirror; the vertically polarized signals are converged to a second photomultiplier by a silver-plated reflecting mirror and a second focusing mirror;
Hyperspectral channel: the echo signals are converged to the second photomultiplier through the iodine molecule absorption tank and the third focusing mirror.
Preferably, the laser is an all-solid-state frequency-locked pulse laser based on diode pumping.
Preferably, the laser emits 532nm laser with single longitudinal mode and stable frequency, the emission energy is 3mJ, the repetition frequency is 1kHz, and the frequency stabilization precision is 10MHz.
Preferably, the receiving aperture of the telescope is about 200mm, and the wave aberration RMS is better than lambda/[email protected].
Preferably, the aperture of the pinhole diaphragm is 1mm.
Preferably, the passband half width of the filter is 150pm; the passband half width of the etalon is 30pm.
Preferably, the length of the iodine molecule absorption tank is 100mm, and the window mirrors are all plated with 532nm antireflection films.
Preferably, the rotation angle of the vibrating mirror is adjusted to be within a range of +/-30 degrees, and the angular resolution is 70urad.
The invention also discloses a method for acquiring the backscattering coefficient and the extinction coefficient of the aerosol, which is based on the high-efficiency compact high-spectrum-resolution laser radar system, and is characterized in that the backscattering coefficient and the extinction coefficient of the aerosol are acquired by solving the following equation set:
wherein η is optical efficiency; Transmitting energy for the system; c represents the speed of light; a is the telescope receiving area; beta is the backscattering coefficient; r represents a detection distance; f a、fm is the transmittance of the iodine molecule absorption cell to aerosol scattering and molecular scattering, subscripts a, m, tot represent the aerosol component influence, the molecular component influence, the total influence of aerosol and molecules, respectively, ||is expressed as parallel polarization direction; t 2 is the double-pass atmospheric transmittance, and P is the peak power of the laser echo received by the laser radar.
Preferably, it comprises the steps of:
step one: powering up each module of the system to work, and emitting single-frequency pulse laser by a laser;
Step two: the telescope receives scattered echo signals of laser and atmospheric action;
Step three: the vibrating mirror rotates to the polarization channel direction and receives signals of the horizontal polarization channel and the vertical polarization channel;
step four: the vibrating mirror rotates to the hyperspectral channel direction, the hyperspectral channel signals are received, the third step and the fourth step are repeated, and the period can be set;
Step five: carrying out processing including background denoising, system constant correction, distance square correction, sliding denoising, geometric overlap factor correction and hyperspectral algorithm inversion on the original data;
step six: the final output contains a data product of the aerosol backscattering coefficient and the extinction coefficient.
The beneficial effects of the invention are that
The high-spectrum-resolution laser radar system is used in combination with the vibrating mirror switching receiving channel in the receiving system, so that the receiving efficiency is further improved, meanwhile, the compact design of the system is realized, in addition, the laser radar system is less influenced by the working environment, the engineering application can be realized, and the whole system is more stable and reliable. The diode-pumped all-solid-state frequency-locking pulse laser is used as a light source of the high-spectrum-resolution laser radar, and compared with a traditional lamp-pumped laser, the laser-pumped all-solid-state frequency-locking pulse laser has higher repetition frequency of emergent laser, namely the time resolution of the laser radar is higher, and the maintenance period of a diode pumping scheme is short and the environmental adaptability is stronger; compared with the traditional polarization beam splitter light splitting scheme, the receiving efficiency of each channel can be greatly improved, one photomultiplier can be saved, the cost is reduced, and the system structure can be more compact; the atomic or molecular absorption tank is used as a frequency discrimination device of the receiving system, the absorption tank is simple in structure, the requirements on the incident angle and the temperature are not high, and compared with the traditional interferometer scheme, the atomic or molecular absorption tank is more suitable for engineering application due to the adverse elements of high installation difficulty, complex light path, small receiving field angle, easy influence of vibration, temperature, pressure and the like on the cavity length.
Drawings
FIG. 1 is a view of a laser radar system according to the present invention
Detailed Description
The high spectral resolution lidar for atmospheric aerosol detection mainly comprises three modules: the device comprises a laser emitting module, a signal receiving module and a signal acquisition processing module. The laser emission module is an all-solid-state frequency-locking pulse laser based on diode pumping, the laser adopts a frequency locking technology to realize single-frequency pulse laser output, and then a Galileo beam expansion lens is used for compressing the divergence angle of emergent laser to obtain a farther detection distance; the signal receiving module consists of a telescope, a small aperture diaphragm, a collimating lens, a narrow-band filter, an etalon, a vibrating lens, an absorption tank, a polarization beam splitter, a focusing lens, a photomultiplier and the like, wherein the high-efficiency receiving of each channel can be realized by using a mode of time division multiplexing of the vibrating lens switching channels; the signal acquisition processing module consists of an acquisition card, an industrial personal computer, a main control board and the like, and processes the acquired information to obtain a desired data product. The scattering spectrum of the laser emitted by the system in the atmosphere is mainly caused by Doppler broadening of scattering particles, and the thermal motion of atmospheric molecules reaches hundreds of meters per second, so that the molecular Rayleigh scattering spectrum width reaches the GHz level. And filtering out the rice scattering signals of the atmospheric aerosol in the laser radar echo signals by utilizing an iodine molecule absorption tank, so that all the transmitted parts are molecular signals, and separating the aerosol rice scattering signals and the molecular Rayleigh scattering signals.
As shown in fig. 1, a compact and stable high spectral resolution lidar system of the present invention comprises:
The laser 1 is an all-solid-state frequency locking pulse laser based on diode pumping, emits 532nm laser with single longitudinal mode and stable frequency, and has the emission energy of 3mJ, the repetition frequency of 1kHz and the frequency stabilization precision of about 10MHz. The reflecting mirror 2 reflects and transmits the laser light and controls the outgoing direction of the laser light. The window mirror 3 plays a certain role in protecting the system, and laser emission and signal reception are carried out through the same window mirror 3.
The all-solid-state frequency-locking pulse laser using diode pumping is considered as a light source of the laser radar with high spectral resolution, compared with a traditional lamp pump laser, the laser has higher repetition frequency of emergent laser, namely the time resolution of the laser radar is higher, and the maintenance period of the diode pumping scheme is short and the environmental adaptability is stronger.
The receiving aperture of the telescope 4 is about 200mm, and the wave aberration RMS is better than lambda/[email protected]. An aperture stop 5 is placed at the focal plane of the telescope 4, the aperture size being about 1mm. The collimating mirror 6 collimates the received signal, and the collimated signal passes through the optical filter 7 and the etalon 8 to suppress background light noise, wherein the passband half-width of the optical filter 7 is about 150pm, and the passband half-width of the etalon 8 is about 30pm.
The rotation angle range of the vibrating mirror 9 is regulated to be +/-30 degrees, the angular resolution is 70urad, the rotation directions are two, namely a polarization channel and a hyperspectral channel, the polarization channel is a signal channel of a traditional Michaelis laser radar, the polarization beam splitter detects two paths of polarization information, and the hyperspectral channel is the signal channel after passing through an iodine molecule absorption tank.
The receiving system is considered to use the vibrating mirror to switch the receiving channels, so that compared with the traditional polarization beam splitter beam splitting scheme, the receiving efficiency of each channel can be greatly improved, meanwhile, a photomultiplier can be saved, and the system structure can be more compact while the cost is reduced.
When the galvanometer 9 rotates to the polarization channel, the echo signal is divided into a horizontal polarized signal and a vertical polarized signal by the polarization beam splitter 10, the horizontal polarized signal is converged on the first photomultiplier 14-1 by the first focusing mirror 12-1, and the vertical polarized signal is converged on the second photomultiplier 14-2 by the silver-plated reflecting mirror 11 and the second focusing mirror 12-2, so that depolarization analysis of the signal is performed.
When the galvanometer 9 rotates to the hyperspectral channel, the echo signal converges the signal to the second photomultiplier tube 14-2 via the iodine molecule absorption cell 13 and the third focusing mirror 12-3. The iodine molecule absorption tank 13 has simple structure, low requirements on incident angle and temperature, and is more suitable for engineering application compared with the traditional interferometer scheme which has the disadvantages of high installation difficulty, complex light path, small receiving angle of view, and easy influence of vibration, temperature, pressure and the like on cavity length. The atomic or molecular absorption tank is used as a frequency discrimination device of the receiving system, has simple structure, low requirements on incident angle and temperature, and is more suitable for engineering application compared with the traditional interferometer scheme which has the disadvantages of high installation difficulty, complex light path, small receiving angle of view, and easy influence of vibration, temperature, pressure and the like.
The mode of selecting the vibrating mirror to rotate and switch the channels has the greatest advantage that echo signals are completely utilized to respectively carry out multichannel detection, so that the upper limit of receiving efficiency is improved, namely, compared with the traditional polarization beam splitter beam splitting scheme, the receiving efficiency of each channel is greatly improved, and the scheme can detect information at a longer distance. Meanwhile, one photomultiplier tube can be saved, the system structure can be more compact while the cost is reduced, the link of calibrating the detector is omitted, and the system detection error can be further reduced.
The invention also discloses a method for acquiring the backward scattering coefficient and the extinction coefficient of the aerosol, which comprises the following steps:
step one: powering up each module of the system to work, and emitting single-frequency pulse laser by a laser;
Step two: the telescope receives scattered echo signals of laser and atmospheric action;
Step three: the vibrating mirror rotates to the polarization channel direction and receives signals of the horizontal polarization channel and the vertical polarization channel;
step four: the vibrating mirror rotates to the hyperspectral channel direction, the hyperspectral channel signals are received, the third step and the fourth step are repeated, and the period can be set;
Step five: carrying out processing including background denoising, system constant correction, distance square correction, sliding denoising, geometric overlap factor correction and hyperspectral algorithm inversion on the original data;
step six: the final output contains a data product of the aerosol backscattering coefficient and the extinction coefficient.
In the sixth step, the formula (1) is established:
Wherein P (R, lambda) is laser echo peak power received by a laser radar, P 0 is emission laser peak power, c is light speed, tau is laser pulse width, A is telescope receiving sectional area, eta is laser radar receiving efficiency, O (R) is laser radar overlapping factor, R is detection distance, beta (R, lambda) is backscattering coefficient, and alpha (R, lambda) is extinction coefficient. Since the backscattering coefficient and the atmospheric extinction coefficient consist of aerosol and molecular contribution, the molecular scattering is stable, and beta and alpha can be obtained through a standard atmospheric model or atmospheric temperature and pressure distribution data above an observation point. Therefore, we can obtain two uncorrelated equations by separating the molecular and aerosol signals with the discriminator through the above equation, i.e. can solve the backscattering coefficient and extinction coefficient of the aerosol. If the frequency discriminator uses an iodine molecule absorption tank, one equation is a laser radar equation containing aerosol and molecule contribution, the other equation is a laser radar equation with molecule contribution as a main component, and the two equations can accurately solve two unknown quantities, namely the backscattering coefficient and extinction coefficient of the aerosol. Two uncorrelated equations are shown in formulas 2 and 3, where η is optical efficiency; Transmitting energy for the system; c represents the speed of light; a is the telescope receiving area; beta is the backscattering coefficient; r represents a detection distance; f a、fm is the transmittance of the iodine molecule absorption cell to aerosol scattering and molecular scattering, subscripts a, m and tot respectively represent aerosol, molecules, the sum of aerosol and molecules, and I is expressed as parallel polarization directions; t 2 is the two-pass atmospheric transmittance.
And (3) solving the equation set (2) and (3) to obtain the acquired aerosol backscattering coefficient and the extinction coefficient. It should be understood that the foregoing examples are merely illustrative of the technical concept and features of the present utility model and are intended to provide those skilled in the art with an understanding of the present utility model and are not to be construed as exhaustive or as limiting the scope of the utility model. All changes and equivalents that come within the meaning and range of the term "about" are intended to be embraced therein.
Claims (10)
1. The high-efficiency compact high-spectral-resolution laser radar system is characterized by comprising a laser (1), a reflecting mirror (2), a window mirror (3), a telescope (4), a small-hole diaphragm (5), a collimating mirror (6), an optical filter (7), an etalon (8), a vibrating mirror (9), a polarization beam splitter (10), a silver plating reflecting mirror (11), a focusing mirror (12), an iodine molecule absorption tank (13) and a photomultiplier (14), wherein laser emitted by the laser (1) is transmitted in a reflecting way through the reflecting mirror (2) and the emergent direction of the laser is controlled; the laser emission and the signal receiving are carried out through the same window mirror (3); the laser further passes through a telescope (4) and a small aperture diaphragm (5), and then a collimating mirror (6) collimates the received signals; the collimated signals are emitted into a vibrating mirror (9) after passing through an optical filter (7) and an etalon (8), the optical filter (7) and the etalon (8) are used for inhibiting background light noise, and the rotation directions of the vibrating mirror are two: a polarization channel and a hyperspectral channel;
Polarization channel: the echo signals are divided into horizontal polarized signals and vertical polarized signals by a polarization beam splitter (10), and the horizontal polarized signals are converged to a first photomultiplier (14-1) by a first focusing mirror (12-1); the vertically polarized signals are converged to the second photomultiplier (14-2) by the silver plating reflecting mirror (11) and the second focusing mirror (12-2);
Hyperspectral channel: the echo signals are converged to the second photomultiplier (14-2) through the iodine molecule absorption tank (13) and the third focusing mirror (12-3).
2. An efficient compact high spectral resolution lidar system as claimed in claim 1, characterized in that the laser (1) is an all-solid-state frequency-locked pulse laser based on diode pumping.
3. A high efficiency compact high spectral resolution lidar system according to claim 2, characterized in that the laser (1) emits a single longitudinal mode and frequency stable 532nm laser with an emission energy of 3mJ, a repetition frequency of 1kHz and a frequency stabilization accuracy of 10MHz.
4. A high efficiency compact high spectral resolution lidar system according to claim 1, characterized in that the telescope (4) has a receiving aperture of 200mm and the wave aberration RMS is better than λ/[email protected].
5. A high efficiency compact high spectral resolution lidar system according to claim 1, characterized in that the aperture of the aperture stop (5) is 1mm.
6. A high efficiency compact high spectral resolution lidar system according to claim 1, characterized in that the passband half-width of the filter (7) is 150pm; the passband half width of the etalon (8) is 30pm.
7. A high efficiency compact high spectral resolution lidar system according to claim 1, characterized in that the length of the iodine molecule absorption cell (13) is 100mm, and the window mirrors are coated with 532nm antireflection film.
8. A high efficiency compact high spectral resolution lidar system according to claim 1, characterized in that the galvanometer (9) is adjusted to a rotation angle range of ±30° with an angular resolution of 70urad.
9. A method of obtaining an aerosol backscatter coefficient and an extinction coefficient based on a high-efficiency compact high spectral resolution lidar system according to any of claims 1-8, characterized in that the aerosol backscatter coefficient and the extinction coefficient are obtained by solving the following system of equations:
wherein η is optical efficiency; Transmitting energy for the system; c represents the speed of light; a is the telescope receiving area; beta is the backscattering coefficient; r represents a detection distance; f a、fm is the transmittance of the iodine molecule absorption cell to aerosol scattering and molecular scattering, subscripts a, m, tot represent the aerosol component influence, the molecular component influence, the total influence of aerosol and molecules, respectively, ||is expressed as parallel polarization direction; t 2 is the double-pass atmospheric transmittance, and P is the peak power of the laser echo received by the laser radar.
10. A method of obtaining an aerosol backscattering coefficient and an extinction coefficient according to claim 9, comprising the steps of:
step one: powering up each module of the system to work, and emitting single-frequency pulse laser by a laser;
Step two: the telescope receives scattered echo signals of laser and atmospheric action;
Step three: the vibrating mirror rotates to the polarization channel direction and receives signals of the horizontal polarization channel and the vertical polarization channel;
step four: the vibrating mirror rotates to the hyperspectral channel direction, the hyperspectral channel signals are received, the third step and the fourth step are repeated, and the period can be set;
Step five: carrying out processing including background denoising, system constant correction, distance square correction, sliding denoising, geometric overlap factor correction and hyperspectral algorithm inversion on the original data;
step six: the final output contains a data product of the aerosol backscattering coefficient and the extinction coefficient.
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