CN211206161U

CN211206161U - Dual-wavelength laser radar aerosol measuring system

Info

Publication number: CN211206161U
Application number: CN201922451124.2U
Authority: CN
Inventors: 杨婷
Original assignee: Institute of Atmospheric Physics of CAS
Current assignee: Institute of Atmospheric Physics of CAS
Priority date: 2019-12-30
Filing date: 2019-12-30
Publication date: 2020-08-07
Anticipated expiration: 2029-12-30

Abstract

The present disclosure provides a dual wavelength lidar aerosol measurement system. The system comprises: an emission optical path which emits detection laser with two wavelengths of 532nm and 1064nm to the atmosphere; a receiving optical path which receives backscattered light of the detection laser passing through the atmospheric aerosol particles, separates signal light of two wavelengths from the backscattered light, and converts the signal light into an electrical signal; and the control and data acquisition device is used for controlling the transmitting light path to transmit the detection laser and storing the electric signal data of the receiving light path, which is obtained by the backward scattering light and corresponds to the laser with two wavelengths. The present disclosure adds 1064nm wavelength detection, so that atmospheric aerosols in the atmosphere can be detected more widely, such as floating aerosol and large-particle sand dust aerosol. Meanwhile, the precision of the polluted vertical structure data can be improved, and the early warning accuracy of the pollution time is improved.

Description

Dual-wavelength laser radar aerosol measuring system

Technical Field

The utility model relates to an environmental monitoring and optics technical field especially relate to a dual wavelength laser radar surveys aerosol system.

Background

At present, atmospheric pollution events occur frequently in China, and public trip and health are seriously affected by heavily polluted weather, so that the global social attention is attracted. The atmosphere acts as an open space, and besides pollution from local emissions, ambient transport effects are also one of the important contributions to atmospheric pollution. According to past historical studies, the annual average contribution of foreign transport to the concentration of local contaminants in Beijing is up to 30% in the case of Beijing. During heavy contamination, the contribution of extraneous influences can even be as high as 70-80%. The vertical structure of pollution can not be obtained by conventional ground observation, but the vertical structure can have good foresight on pollution sources and can well perform early warning on pollution events.

However, the traditional laser radar aerosol measurement system only adopts 532nm detection laser to detect, the observation scale of the aerosol particle size is limited, the precision of the pollution vertical structure data is poor, and the monitoring of the pollution event is insufficient.

SUMMERY OF THE UTILITY MODEL

Technical problem to be solved

The present disclosure provides a dual wavelength lidar aerosol measurement system to at least partially address the above-identified technical problems.

(II) technical scheme

The utility model provides a dual wavelength laser radar surveys aerosol system includes: an emission optical path which emits detection laser with two wavelengths of 532nm and 1064nm to the atmosphere, comprising: the laser system comprises a trigger, a laser system, a beam expanding lens and a reflector; wherein, laser system includes: a pulsed laser and a harmonic generator; under the trigger of the trigger, the pulse laser emits laser with the wavelength of 1064nm, the laser forms 532nm and 1064nm double-wavelength channel collinear transmission laser through the harmonic generator, and the double-wavelength channel collinear transmission laser is injected into the atmosphere after passing through the beam expander and the reflector to form detection laser; a receiving optical path which receives backscattered light of the detection laser passing through the atmospheric aerosol particles, separates signal light of two wavelengths from the backscattered light, and converts the signal light into an electrical signal; and the control and data acquisition device is used for controlling the transmitting light path to transmit the detection laser and storing the electric signal data of the receiving light path, which is obtained by the backward scattering light and corresponds to the laser with two wavelengths.

In some embodiments of the present disclosure, the pulsed laser is a flash lamp pumped Nd: YAG laser.

In some embodiments of the present disclosure, the receive optical path includes: the device comprises a telescope, a dichroic mirror, a photodiode, a polarizing prism and two photomultiplier tubes; wherein, the telescope receives the backscattered light of surveying laser through atmospheric aerosol particulate matter, and 532 nm's emergent light and 1064 nm's emergent light are separated by the dichroic mirror to this backscattered light:

(1) for 532nm emergent light, a horizontal polarization component and a vertical polarization component are separated through a polarizing prism, and are converted into electric signals by corresponding photomultiplier tubes respectively and sent to a control and data acquisition device.

(2) The 1064nm emergent light is converted into an electric signal by a photodiode and sent to a control and data acquisition device.

In some embodiments of the disclosure, the telescope is a schmidt cassegrain telescope.

In some embodiments of the present disclosure, in the receive optical path: an aperture diaphragm and a calibration lens are arranged between the telescope and the dichroic mirror; and an interference filter capable of filtering background solar radiation is arranged in front of the light paths of the photodiode and the photomultiplier.

In some embodiments of the present disclosure, the transmit optical path, the receive optical path, and the photomultiplier tube's modulator and drive power supply are assembled to an optical mounting plate and enclosed within an integral chamber.

In some embodiments of the present disclosure, the beam expander is a 5-fold beam expander.

In some embodiments of the present disclosure, the control and data acquisition device comprises: three-wavelength digital oscilloscope, data acquisition module and control module: the trigger of the emission light path is connected to the control module through an RS232 serial interface; two input ends of three input ends of the three-wavelength digital oscilloscope are connected to the output ends of the two photomultiplier tubes, the third input end is connected to the output end of the photodiode, and the output end is connected to the data acquisition module through a GPIB interface; the data acquisition module and the control module are integrated in the data acquisition control computer.

(III) advantageous effects

According to the technical scheme, the dual-wavelength laser radar aerosol measurement system at least has one of the following beneficial effects:

(1) the detection of 1064nm wavelength is added, so that the atmospheric aerosol in the atmosphere, such as floating aerosol and large-particle dust aerosol, can be detected more widely. Meanwhile, the precision of the polluted vertical structure data can be improved, and the early warning accuracy of the pollution time is improved.

(2) YAG laser is adopted in the emitting light path part, and besides traditional 532nm wavelength laser, 1064nm wavelength laser can be excited without increasing the volume of the device obviously.

(3) In a receiving light path, a Schmidt Cassegrain telescope receives a reflected light beam, a dichroic mirror separates two wavelengths of light for processing respectively, a photodiode converts the reflected light with the wavelength of 1064nm into an electric signal, a photomultiplier converts the reflected light with the wavelength of 532nm into an electric signal, and a digital oscilloscope converts the electric signal to realize data collection of the double-wavelength optical signal.

(4) The transmitting light path, the receiving light path and the driving power supply of the photomultiplier are all integrated on the optical plate and are arranged in an integral cabin, and the integration level of the whole device is high.

Drawings

Fig. 1 is a schematic structural diagram of a dual-wavelength lidar aerosol measurement system according to an embodiment of the disclosure.

Fig. 2 is a layout diagram of a dual-wavelength lidar aerosol measurement system on an optical plate according to an embodiment of the disclosure.

[ description of main reference numerals in the drawings ] of the embodiments of the present disclosure

100-an emission light path;

110-a flip-flop;

120-a laser system;

121-pulse Nd is YAG laser; 122-a harmonic generator;

130-a beam expander;

140-a mirror;

200-a receive optical path;

211-a telescope; 212-small aperture diaphragm; 213-a collimating lens;

220-a dichroic mirror;

231-a photodiode;

240-polarizing prism;

251. 252-a photomultiplier tube; 253. 254-photomultiplier regulator and drive power supply;

300-control and data acquisition means;

311-digital oscilloscope; 320-data acquisition control computer.

Detailed Description

The utility model provides a dual wavelength laser radar surveys aerosol system, its detection that has increased 1064nm wavelength for the aerosol particle size spectrum size that can pay attention to is bigger, can improve the precision of polluting vertical structure data, improves the early warning accuracy of pollution time.

Certain embodiments of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the disclosure are shown. Indeed, various embodiments of the disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

In one embodiment of the present disclosure, a dual wavelength lidar aerosol measurement system is provided. Fig. 1 is a schematic structural diagram of an atmospheric aerosol stereoscopic monitoring system according to an embodiment of the disclosure. Fig. 2 is a layout view of an atmospheric aerosol stereoscopic monitoring system on an optical plate according to an embodiment of the disclosure. As shown in fig. 1 and 2, the dual-wavelength lidar aerosol measurement system includes:

an emission optical path 100 that emits detection laser light of two wavelengths 532nm and 1064nm to the atmosphere (in fig. 1, laser light components of the wavelengths 532nm and 1064nm are indicated by a broken line and a solid line, respectively);

a receiving optical path 200 that receives backscattered light of the detection laser passing through the atmospheric aerosol particles, separates signal light of two wavelengths from the backscattered light, and converts the signal light into an electrical signal;

and a control and data acquisition device 300 for controlling the emission light path to emit the detection laser and storing the electrical signal data of the receiving light path obtained by the backward scattering light corresponding to the laser light of two wavelengths.

As described above, in the embodiment, the characteristic of atmospheric aerosol is represented by the 532nm wavelength detection and the 1064nm detection together by adding the 532nm wavelength detection to the system, so that the particle size spectrum of the aerosol which can be focused on is larger, the precision of the polluted vertical structure data can be improved, and the early warning accuracy of the pollution time can be improved.

The following describes each component of the atmospheric aerosol stereoscopic monitoring system in detail. Table 1 is a summary table of the model and parameter of each component in this embodiment.

Table 1 parts description of dual wavelength lidar aerosol measurement system

Referring to fig. 1 and fig. 2, in order to generate laser with two wavelengths, in this embodiment, the emission light path includes: a trigger 110, a laser system 120, a beam expander 130, and a mirror 140. The control and data acquisition device controls the trigger to send out a trigger signal. Under the trigger of the trigger signal, the laser system emits 532nm and 1064nm dual-wavelength channel collinear transmission laser. The collinear transmission laser of the dual-wavelength channel is emitted into the atmosphere by the reflector after being expanded by the beam expander to form detection laser.

In this embodiment, the laser system 120 includes: YAG laser 121 and harmonics generator 122. YAG laser, which uses neodymium solid-state laser-doped yttrium aluminum garnet as a laser medium, is widely used as a light source in mie-scattering laser radars. YAG laser generates laser light at a wavelength of 1064 nm. In this embodiment, a harmonic generator (SHG) is added after the pulsed Nd: YAG laser, and laser light with a wavelength of 532nm is generated. These two wavelengths can be used as light sources for mie scattering lidar, resulting in co-linear transmission lasers of the 532nm and 1064nm dual wavelength channels. The laser system has the output energy of 30mJ at 532nm and 20mJ at 1064nm, and the pulse frequency is 20Hz at most, but the pulse frequency of the system is 10Hz and the pulse duration is about 7ns in normal operation.

For the sake of understanding, the laser beam having a wavelength of 532nm (indicated by a broken line in the figure) and the laser beam having a wavelength of 1064nm (indicated by a solid line in the figure) are separated in the emission optical path of fig. 1, but in reality, only one laser beam is emitted from the laser system and the same mirror is shared. The laser beam had both 532nm and 1064nm components.

Referring to fig. 2, in the present embodiment, the beam expander 130 is a 5-fold beam expander. After the laser beam emitted from the laser system is collimated by the 5-fold beam expander, the laser beam is reflected by the reflector and then emitted vertically to the atmosphere. The laser output power level is 4 levels, and the laser needs to be used under the condition of ensuring safety.

Referring to fig. 1 and fig. 2, in order to implement the detection of the laser with two wavelengths, in the present embodiment, the receiving optical path 200 includes: telescope 211, dichroic mirror 220, photodiode 231, polarizing prism 240, and two photomultiplier tubes (251, 252). Wherein, the backward scattered light of the detection laser passing through the atmospheric aerosol particles is received by the telescope 210, and the received light beam is separated into 532nm emergent light and 1064nm emergent light through the dichroic mirror. Typically, photomultiplier tubes (PMTs) are used at visible wavelengths and photodiodes (APDs) are used at near infrared wavelengths. At the instant after the laser pulse is received, the waveform of the electrical signal as a function of time is recorded as:

(1) for incident laser with the wavelength of 532nm, a horizontal polarization component and a vertical polarization component are separated by a polarizing prism 240, and are converted into electric signals by photomultiplier tubes (251, 252) respectively and sent to a control and data acquisition device.

(2) Incident laser with the wavelength of 1064nm is converted into an electric signal through a photodiode (231) and sent to a control and data acquisition device.

The system can additionally obtain an echo signal at 1064nm, and on the basis of the traditional 532nm laser radar, the information of two wavelengths is combined with each other, so that more information can be obtained. If the diameter of the scatterer is large, such as a water cloud droplet (10 μm or more in diameter), the wavelength ratio P (1064)/P (532) will be close to 1. This is because for large particles, the dependence of scattering on wavelength is small. Aerosols have small wavelength ratios (-0.1 to-1.2). Large particles are generally large in wavelength ratio. Clouds have large P (1064)/P (532) values, and a quick look at P (1064)/P (532) indicates that it is necessary to know about forest fire-like conditions. In the case where air pollution is severe, a similar wavelength ratio distribution is also observed.

In this embodiment, the receiving telescope 211 is a schmidt cassegrain telescope with a diameter of 20 cm, and the field of view of the receiver, which is typically 1mrad with a resultant focal length of 2m and an aperture of 2mm, can be adjusted by placing an iris on its focal plane.

In addition, in order to further improve the measurement accuracy, an aperture stop 212 and a calibration lens 213 having a focal length of 100mm are further provided between the telescope and the dichroic mirror in the reception optical path to calibrate the reception light beam. Wherein, in front of the light path of the photodiode (APD) and the photomultiplier tube (PMT), an interference filter is also arranged to remove background solar radiation. The interference filter is a narrow-band filter which can filter out light with other wavelengths except the corresponding wavelength.

The lidar head is assembled on an optical plate having a size of 450mm × 900mm and enclosed in an integral chamber, and includes a transmission optical path, a reception optical path, and a photomultiplier tube adjuster 253 and a photomultiplier tube driving power source 254.

The control and data acquisition device comprises: a three-wavelength digital oscilloscope 311, a data acquisition module and a control module. Two input ends of three input ends of the three-wavelength digital oscilloscope are connected to the output ends of the two photomultiplier tubes, the third input end is connected to the output end of the photodiode, and the output end of the photodiode is connected to the data acquisition module through a GPIB interface. And the trigger of the transmitting light path is connected to the control module through an RS232 serial interface.

In this embodiment, the data acquisition module and the control module are integrated in the data acquisition control computer 320. The data acquisition module stores the output signal of the digital oscilloscope; the control module controls the trigger to send out a trigger signal, and meanwhile, parameters in the digital oscilloscope can be set.

The system of the data acquisition control computer 320 is L inux system, the lidar measurement software is written in C language, the main functions of the measurement software program include timing, controlling the laser (preheat, laser start, laser stop), controlling the digital oscilloscope (initialize, parameter set, data record and data transmission to the computer) and storing the data on the computer's hard disk.

So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Furthermore, the above definitions of the various elements and methods are not limited to the particular structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by one of ordinary skill in the art, for example:

(1) prisms with functions of filtering, correcting, eliminating distortion and the like can be added in the transmitting light path and the receiving light path according to needs, and detailed description is omitted;

(2) the specific types of the photodiode and the photomultiplier can be selected according to the requirements;

(3) instead of a flash-lamp pumped Nd: YAG laser, other pulsed lasers capable of emitting 1064nm laser light can be used.

From the above description, those skilled in the art should clearly recognize that the disclosed dual wavelength lidar aerosol measurement system.

In conclusion, the method breaks through the limitation that only ground data can be obtained in conventional ground observation, and achieves the purpose of actively detecting the vertical distribution characteristic of the atmospheric pollutants by emitting the laser radar outwards. Compare in traditional 532nm single channel laser radar, the 1064nm passageway that this laser radar adds can survey the atmospheric aerosol in the atmosphere more extensive, like float and sink aerosol, large granule sand and dust aerosol. And moreover, the vertical distribution information of the cloud can be obtained, so that regional air quality monitoring can be further carried out by combining with refined early warning and forecasting, and a necessary means is provided for joint defense joint control of pollution in a heavily polluted region.

It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure.

And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure. Furthermore, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.

Furthermore, the word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims

1. A dual wavelength lidar aerosol measurement system, comprising:

an emission optical path which emits detection laser with two wavelengths of 532nm and 1064nm to the atmosphere, comprising: the laser system comprises a trigger, a laser system, a beam expanding lens and a reflector; wherein the laser system comprises: a pulsed laser and a harmonic generator; under the trigger of the trigger, the pulse laser emits laser with the wavelength of 1064nm, the laser forms 532nm and 1064nm double-wavelength channel collinear transmission laser through the harmonic generator, and the double-wavelength channel collinear transmission laser is injected into the atmosphere after passing through the beam expander and the reflector to form detection laser;

a receiving optical path which receives backscattered light of the detection laser passing through the atmospheric aerosol particles, separates signal light of two wavelengths from the backscattered light, and converts the signal light into an electrical signal; and the control and data acquisition device is used for controlling the transmitting light path to transmit the detection laser and storing the electric signal data of the receiving light path, which is obtained by the backward scattering light and corresponds to the laser with two wavelengths.

2. The dual wavelength lidar aerosol measurement system of claim 1 wherein the pulsed laser is a flash lamp pumped Nd: YAG laser.

3. The dual wavelength lidar aerosol measurement system of claim 1 wherein the receive optical path comprises: the device comprises a telescope, a dichroic mirror, a photodiode, a polarizing prism and two photomultiplier tubes;

wherein, the telescope receives the backward scattering light of the detection laser passing through the atmospheric aerosol particles, and the backward scattering light is separated into 532nm emergent light and 1064nm emergent light by a dichroic mirror:

(1) for 532nm emergent light, a horizontal polarization component and a vertical polarization component are separated through a polarizing prism, are converted into electric signals by corresponding photomultiplier tubes respectively, and are sent to a control and data acquisition device;

4. The dual wavelength lidar aerosol measurement system of claim 3 wherein the telescope is a Schmidt Cassegrain telescope.

5. The dual wavelength lidar aerosol measurement system of claim 3 wherein, in the receive optical path:

an aperture diaphragm and a calibration lens are arranged between the telescope and the dichroic mirror;

and an interference filter capable of filtering background solar radiation is arranged in front of the light paths of the photodiode and the photomultiplier.

6. The dual wavelength lidar aerosol measurement system of claim 3 wherein the transmit optical path, receive optical path, and the photomultiplier's regulators and drive power supply are assembled to an optical mounting plate and enclosed within an integral chamber.

7. The dual wavelength lidar aerosol measurement system of any of claims 1-5 wherein the beam expander is a 5-fold beam expander.

8. The dual wavelength lidar aerosol measurement system of any of claims 2 to 5 wherein the control and data acquisition device comprises: three-wavelength digital oscilloscope, data acquisition module and control module:

the trigger of the emission light path is connected to the control module through an RS232 serial interface;

two input ends of three input ends of the three-wavelength digital oscilloscope are connected to the output ends of the two photomultiplier tubes, the third input end is connected to the output end of the photodiode, and the output end of the photodiode is connected to the data acquisition module through a GPIB interface;

the data acquisition module and the control module are integrated in a data acquisition control computer.