CN104729998A - Atmosphere visibility measurement device based on optical cavity ring down spectroscopy technology - Google Patents

Abstract

The invention provides an atmospheric visibility measurement device based on optical cavity ring-down spectrum technology, and relates to a meteorological observation device. It consists of a saddle-shaped housing, a pair of high-reflectivity cavity mirrors are located on both sides of the housing notch to form a ring-down cavity, and the laser emitter emits laser light through the polarizer, 1/4 wave plate and coupling lens in turn and enters the first After one high-reflectivity cavity mirror, one route is reflected by the first high-reflectivity cavity mirror through the 1/4 wave plate and enters the polarizer reflection output, and the other route passes through the second high-reflectivity after oscillating in the ring-down cavity The cavity mirror is transmitted to the photomultiplier tube and transmitted to the computer through the data acquisition card. The invention solves the technical problem in the prior art that there is a deviation between the sampling of the sample to be tested and the actual measurement of the atmospheric visibility, which causes measurement errors. The beneficial effect of the present invention is that: the open ring-down cavity is in direct contact with the atmosphere, and can comprehensively measure changes in atmospheric extinction coefficients caused by gas molecules, aerosols, and rain, thereby realizing accurate measurement of atmospheric visibility.

Description

Atmospheric visibility measurement device based on optical cavity ring-down spectroscopy

technical field

The invention relates to a meteorological observation device, in particular to a device for measuring atmospheric visibility by using optical cavity ring-down spectrum technology.

Background technique

As one of the elements of meteorological observation, atmospheric visibility is a physical quantity that characterizes the transparency of the atmosphere. The measurement of atmospheric visibility is not only used in the weather analysis of the daily meteorological department, but also widely used in highways, aviation, navigation and other transportation departments, military and other fields. At the same time, according to "QX/T 113-2010 Haze Observation and Forecast Grades", atmospheric visibility is the main basis for judging haze grades, so it is of great significance to study atmospheric visibility measurement devices.

As a complex physical quantity, visibility mainly depends on the atmospheric extinction coefficient. The extinction coefficient is the energy attenuation caused by various factors during the transmission of light waves in the atmosphere, which is caused by the absorption and scattering of light radiation by the atmosphere, including molecular absorption, molecular scattering, aerosol absorption, aerosol scattering, rain absorption and Rain scatter.

At present, the atmospheric visibility measurement devices mainly include the transmission type visibility meter and the scattering type visibility meter. Transmissive visibility meters are based on the measurement of the transmittance of light radiation in the atmosphere. Transmissometers are generally divided into two types: double-ended and single-ended. The double-ended type is to install the transmitter and receiver at both ends of the baseline. The single-ended type is to install the transmitter and receiver on the open end of the baseline, and install a reflector on the other end of the baseline, so that the measurement optical path becomes a round-trip optical path. The transmission-type visibility meter directly measures the atmospheric extinction coefficient, but in order to ensure the measurement accuracy, a longer baseline is often required. At the same time, in order to measure low visibility and high visibility, a double-baseline system is required, so the transmission-type visibility meter has higher requirements for the site . The scattering visibility meter emits infrared light radiation, detects the scattering signal in a certain direction, and determines the total scattering coefficient according to the relationship between the scattering signal and the total scattering amount at a specific angle, and finally inverts the visibility according to the formula. Scattering visibility meter can be divided into forward scatter meter and back scatter meter. The diffuse visibility meter is the most widely used visibility meter at present, but the diffuse visibility meter only measures the atmospheric scattering coefficient and does not measure the atmospheric absorption coefficient; in different regions of my country, the ratio of the atmospheric absorption coefficient to the atmospheric scattering coefficient is different, and Sometimes the atmospheric absorption coefficient can be compared with the atmospheric scattering coefficient, so the scattering visibility meter has a large measurement error.

Optical cavity ring-down spectroscopy technology can directly measure the extinction coefficient. At present, optical cavity ring-down spectroscopy technology has been used to measure the extinction coefficient of aerosols, which is measured by pumping aerosols in the atmosphere into the ring-down cavity. Chinese patent application publication number CN103616334A, application publication date March 5, 2014, titled "An optical cavity ring-down aerosol extinction instrument" and Chinese patent application publication number CN103712914A, application publication date April 9, 2014, title The public scheme of "a laser cavity ring-down spectrometer for simultaneous detection of aerosol extinction and scattering coefficient" is a technical scheme for measuring the aerosol extinction coefficient by pumping the aerosol in the atmosphere into the ring-down cavity. Visibility is related to the total extinction coefficient of the atmosphere. The total extinction coefficient of the atmosphere is not only the aerosol extinction coefficient, but also includes the extinction coefficient of gas molecules and the extinction coefficient caused by rain. Therefore, there is a certain measurement error in measuring visibility with an aerosol extinction meter. Chinese patent application publication number CN104062236A, the application publication date is September 24, 2014, and the invention patent publication titled "An Atmospheric Visibility Detection Device Based on Cavity Ring-Down Technology" provides another device. The device includes sequentially arranged light source, lead-in fiber, fiber resonator, lead-out fiber, photodetector and a data processing unit for calculating the light loss data to obtain the visibility value of the detected sample. A lead-in collimator is set between the lead-in fiber and the fiber resonator, a lead-out collimator is set between the fiber resonator and the lead-out fiber, the fiber resonator includes a first coupler, a special fiber and a second coupler, the first coupler The input end of the coupler is connected to the input fiber, the output end of the first coupler is connected to the input end of the special fiber; the output end of the special fiber is connected to the input end of the second coupler; the output end of the second coupler is respectively connected to the first The input end of the coupler is connected with the optical detector; the special optical fiber is used to make the light wave contact and absorb the sample to be measured in the external environment. The data processing unit obtains the loss of the light wave in the resonator according to the characteristics of the resonator, and finally determines the visibility value of the measured sample through the light loss. The device is connected by optical fibers between the light source and the resonant cavity, between the resonant cavity and the optical detector, and uses a special optical fiber to make the light wave contact and absorb the sample to be measured in the external environment. However, there are the following problems: the need to use special optical fibers, which is not only costly, but also inconvenient to use; the absorption of the sample to be tested in the external environment through the special optical fiber still deviates from the actual sample to be tested, resulting in measurement errors.

Contents of the invention

In order to solve the technical problem in the prior art that there is a deviation between the sampling of the sample to be tested and the actual measurement error in the measurement of atmospheric visibility, the present invention provides an atmospheric visibility measurement device based on optical cavity ring-down spectroscopy. The ring-down cavity is an open It is in direct contact with the atmosphere, comprehensively measures changes in the atmospheric extinction coefficient caused by gas molecules, aerosols, and rain, and realizes accurate measurement of atmospheric visibility.

The technical solution of the present invention is: an atmospheric visibility measurement device based on optical cavity ring-down spectroscopy, which includes a housing with a saddle-shaped sealed cavity structure, and a laser transmitter, a polarizer, a 1/4 Wave plate, coupling lens, high-reflectivity cavity mirror, photomultiplier tube and data acquisition card. A pair of high-reflectivity cavity mirrors are located on both sides of the housing notch to form a ring-down cavity. The laser emitted by the laser transmitter passes through the polarizer in turn , 1/4 wave plate and coupling lens are injected into the first high-reflectivity cavity mirror, and the laser is divided into two paths. One path of laser light is reflected by the first high-reflectivity cavity mirror and injected into the polarizer through the 1/4 wave plate to reflect and output. The other laser beam oscillates back and forth in the ring-down cavity and transmits it to the photomultiplier tube through the second high-reflectivity cavity mirror, and the photomultiplier tube is electrically connected to the computer through the data acquisition card. It adopts an open ring-down cavity, which is in direct contact with the atmosphere, and comprehensively measures the changes in the atmospheric extinction coefficient caused by gas molecules, aerosols, and rainwater to achieve accurate measurement of atmospheric visibility.

Preferably, the casing is also provided with a cavity mirror box, and the corresponding side walls of the cavity mirror box are respectively provided with I light transmission port and II light transmission port, and the high reflectivity cavity mirror is fixed in the cavity of the cavity mirror box. Ⅱ Between the light-transmitting ports. Prevent the high reflectivity cavity mirror from being polluted by the atmosphere to ensure accurate measurement.

Preferably, the cavity mirror box is provided with a window plate coated with a high-transparency film, and the window plate covers the light transmission port I.

As a preference, an air inlet is provided on the top of the cavity mirror box close to the light transmission port II; by filling the inlet with high-purity nitrogen, an air curtain is formed on the surface of the high-reflectivity cavity mirror to protect the high-reflectivity cavity mirror from atmospheric pollution.

Compared with the prior art, the beneficial effect of the present invention is that the ring-down cavity is an open structure, directly in contact with the atmosphere, and can comprehensively measure the change of the atmospheric extinction coefficient caused by gas molecules, aerosols, and rainwater, and realize accurate measurement of atmospheric visibility. Measurement.

Description of drawings

Accompanying drawing 1 is schematic diagram of the present invention;

Accompanying drawing 2 is a sectional view of the endoscope box.

In the figure: 1-laser transmitter; 2-mirror; 3-polarizer; 4-1/4 wave plate; 5-coupling lens; 6-cavity mirror box; 7-high reflectivity cavity mirror; 8-photoelectric multiplier Tube; 9-data acquisition card; 10-computer; 11-housing; 61-I light transmission port; 62-II light transmission port; 63-air inlet; 64-window; 111-ring ring.

Detailed ways

The technical solutions of the present invention will be further specifically described below through the embodiments and in conjunction with the accompanying drawings.

Example 1:

As shown in Figures 1 and 2, the dotted lines in the drawings indicate the optical path, and the arrows indicate the direction of the optical path; the thin solid lines indicate electrical connections. An atmospheric visibility measurement device based on optical cavity ring-down spectroscopy technology, which includes a housing 11 with a saddle-shaped sealed cavity structure, and the housing 11 is a sealed cavity structure. There is a notch in the lower part of the housing 11, and the notch is recessed into the cavity of the housing 11. A pair of high-reflectivity cavity mirrors 7 are arranged in the cavity of the casing 11 , and the high-reflectivity cavity mirrors 7 are located on both sides of the notch of the casing 11 . A pair of high-reflectivity cavity mirrors 7 form a ring-down cavity 111 . The ring-down cavity 111 is an open structure, located outside the sealed cavity of the casing 11, and directly in contact with the atmosphere. In order to prevent the high-reflectivity cavity mirror 7 from being polluted by the atmosphere, resulting in measurement errors, the casing 11 is also provided with a cavity mirror box 6 . There are two cavity mirror boxes 6, and a high reflectivity cavity mirror 7 is fixed in each cavity mirror box 6 cavity. The cavity mirror box 6 is a cylindrical cavity structure. The side wall of the cavity mirror box 6 is respectively provided with an I light transmission port 61 and a II light transmission port 62 , and the I light transmission port 61 and the II light transmission port 62 are symmetrically arranged with the central axis of the cavity mirror box 6 as a symmetrical axis. The cavity mirror 7 with high reflectivity is located between the I light-transmitting port 6 and the II light-transmitting port 62 . The outer surface of the side wall of the cavity mirror box 6 is provided with a window sheet 64, and the outer surface of the window sheet 64 is coated with a high-transparency film. The window 64 covers the I light-transmitting opening 61 . The top of the cavity mirror box 6 is provided with an air inlet 63 close to the II light transmission port 62 . Fill the high-purity nitrogen gas from the air inlet 63 and then come out from the II light-transmitting port 62 to form an air curtain on the surface of the high-reflectivity cavity mirror 7, thereby preventing atmospheric pollution of the high-reflectivity cavity mirror 7. A laser transmitter 1 , a mirror 2 , a polarizer 3 , a quarter wave plate 4 , a coupling lens 5 , a photomultiplier tube 8 , a data acquisition card 9 and a computer 10 are also arranged in the cavity of the housing 11 . The reflection mirror 2 has two sides, the first reflection mirror 2 is connected between the laser transmitter 1 and the polarizer 3 , and the second reflection mirror 2 is connected between the 1/4 wave plate 4 and the coupling lens 5 . Laser transmitter 1, first mirror 2, polarizer 3, 1/4 wave plate 4, second mirror 2, coupling lens 5, first high reflectivity cavity mirror 7, second high reflectivity The cavity mirror 7 and the photomultiplier tube 8 are arranged in sequence. The photomultiplier tube 8 is electrically connected to the data acquisition card 9, and the data acquisition card 9 is connected to the computer 10 through wires.

The laser transmitter 1 emits p-polarized light. In order not to affect the ring-down signal, the laser pulse width should be short enough. In this embodiment, the laser wavelength is 532 nm, the pulse width is 1 ns, and the laser mode is the fundamental mode. The p-polarized light enters the first reflector 2 and is refracted, then passes through the polarizer 3 and the 1/4 wave plate 4 in sequence, and becomes circularly polarized light. The circularly polarized light enters the second reflector 2 and is refracted, then is coupled to the ring-down cavity 111 by the coupling lens 5 . Circularly polarized light passes through the window plate 64 covering the first cavity mirror box 6, and enters the first high-reflectivity cavity mirror 7 through the I light transmission port 61 of the first cavity mirror box 6, and is divided into two paths. One path of circularly polarized light is reflected by the first high-reflectivity cavity mirror 7, passes through the light transmission port 61 of the first cavity mirror box 6, passes through the window 64, is refracted by the second reflector 2, and enters 1/4 After the wave plate 4 becomes s-polarized light, the s-polarized light enters the polarizer 3 to reflect and isolate the output, preventing it from entering the laser transmitter 1 again and causing damage to the laser transmitter 1 . The other circularly polarized light passes through the first high-reflectivity cavity mirror 7, comes out from the II light transmission port 62 of the first cavity mirror box 6, and directly contacts the atmosphere to be measured, and passes through the II transmittance port 62 of the second cavity mirror box 6. The optical port 62 is reflected by the second high-reflectivity cavity mirror 7 and oscillates back and forth between the first high-reflectivity cavity mirror 7 and the second high-reflectivity cavity mirror 7 to form a measurement optical path. Then pass through the second high-reflectivity cavity mirror 7, the I light-transmitting port 61 of the second cavity mirror box 6, and the window plate 64 to output the ring-down signal. The ringdown signal is detected by the photomultiplier tube 8 . The data acquisition card 9 collects the ring down signal and transmits it to the computer 10 . The computer 10 processes and obtains the ring down time. Measure the cavity ring-down time t ₀ and the atmospheric ring-down time t respectively, by the formula The extinction coefficient β of the atmosphere can be calculated (c in the formula is the speed of light). Different ring down times correspond to different extinction coefficients, from which the atmospheric extinction coefficient and visibility can be calculated.

Claims (4)

1. the atmospheric visibility measurement mechanism based on cavity ring down spectroscopy technology, it is characterized in that: it comprises the housing (11) in saddle seal chamber structure, generating laser (1) is provided with in housing (11) cavity, polaroid (3), quarter wave plate (4), coupled lens (5), high reflectance chamber mirror (7), photomultiplier (8) and data collecting card (9), described high reflectance chamber mirror (7) has and is positioned at housing (11) recess both sides for a pair and is formed and decline and swing chamber (111), the laser that described generating laser (1) sends is successively through polaroid (3), quarter wave plate (4) and coupled lens (5) inject first surface high reflectance chamber mirror (7), laser is divided into two-way, one road laser is reflected through quarter wave plate (4) by first surface high reflectance chamber mirror (7) and injects polaroid (3) reflection output, another road laser is transferred to photomultiplier (8) through second high reflectance chamber mirror (7) after oscillate declining to swing in chamber (111), photomultiplier (8) is electrically connected with computing machine (10) by data collecting card (9).

2. the atmospheric visibility measurement mechanism based on cavity ring down spectroscopy technology according to claim 1, it is characterized in that: described housing (11) is also provided with chamber mirror case (6), the corresponding sidewall of chamber mirror case (6) is respectively equipped with I printing opacity mouth (61) and II printing opacity mouth (62), is positioned between I printing opacity mouth (61) and II printing opacity mouth (62) in mirror (7) lock chamber mirror case (6) cavity of described high reflectance chamber.

3. the atmospheric visibility measurement mechanism based on cavity ring down spectroscopy technology according to claim 2, is characterized in that: described chamber mirror case (6) is provided with the diaphragm (64) of plating high transmittance film, and described diaphragm (64) covers I printing opacity mouth (61).

4. the atmospheric visibility measurement mechanism based on cavity ring down spectroscopy technology according to Claims 2 or 3, is characterized in that: mirror case (6) top, described chamber is provided with air intake opening (63) near II printing opacity mouth (62).