Laser light transmitting and receiving device for air pollutant observation lidar

Abstract

The present invention relates to an atmospheric pollutant observation lidar, and more specifically, to a laser light transmitting and receiving device for an atmospheric pollutant observation lidar that uses a single laser source to observe tropospheric ozone and receives the scattered signal through a single telescope, enabling observation from the lower to the upper layers of the troposphere, and can be constructed inexpensively with a simple structure.

Description

Technology Field

[0001] The present invention relates to an atmospheric pollutant observation lidar, and more specifically, to a laser light transmitting and receiving device for an atmospheric pollutant observation lidar that uses a single laser source to observe tropospheric ozone and receives the scattered signal through a single telescope, enabling observation from the lower to the upper layers of the troposphere, and can be constructed inexpensively with a simple structure. Background Technology

[0002] Generally, chemical methods that involve directly collecting and processing samples, and spectroscopic methods that measure remotely without the need for sample collection, are used as measurement techniques for pollutants present in the atmosphere.

[0003] The former, chemical methods, have many disadvantages because the sample pretreatment process is complex and they provide only localized information. On the other hand, the latter, represented by laser-based LIDAR measurements, has the advantage of easily observing the three-dimensional distribution of contaminants.

[0004] The optical system constituting a lidar basically consists of a transmitting optical system that irradiates a laser into the atmosphere and a receiving optical system that receives signals that are scattered by air molecules or dust and return.

[0005] Previously, to observe atmospheric ozone using lidar, measurements were performed using the differential absorption method based on backscattered signals by irradiating the atmosphere with resonant wavelengths that exhibit high absorption in the ultraviolet region and non-resonant wavelengths that exhibit low absorption.

[0006] In addition, abroad, observations are being conducted using the Raman transition wavelengths of hydrogen or deuterium with KrF excimer lasers as excitation sources for tropospheric ozone measurement, and observations are being performed using the Raman transition wavelengths of hydrogen or deuterium with XeCl excimer lasers as excitation sources for stratospheric ozone observation.

[0007] However, using such excimer lasers presents the problem that the system is complex and requires high maintenance costs. Prior art literature

[0008] Republic of Korea Registered Patent No. 10-0540222 (December 23, 2005) The problem to be solved

[0009] The present invention was created to solve the aforementioned problems. The objective of the present invention is to provide a laser light transceiver for an atmospheric pollutant observation lidar capable of providing ozone concentrations from the lower to the upper layers of the troposphere, by using a stable solid-state laser light source instead of a complex and expensive gas laser, the Excimer laser light source, and by using a single optical system, thereby improving efficiency and addressing the system complexity and optical alignment instability that are inherent risks of using separate optical systems for transmitting the laser beam and receiving scattered signals. means of solving the problem

[0010] For the purpose of the above, the present invention comprises a laser light transmitting device for observing tropospheric ozone, comprising: a laser light source that generates harmonic waves for ozone measurement; a Raman wavelength generator that receives the harmonic waves for ozone measurement and generates a laser beam of a set wavelength; a transmitting unit that simultaneously irradiates the harmonic waves for ozone measurement as a resonant wavelength and the laser beam generated by the Raman wavelength generator as a non-resonant wavelength into the atmosphere; a photodecomposer that receives the light irradiated and scattered through the transmitting unit and decomposes it into a resonant wavelength and a non-resonant wavelength, respectively; and a control module that receives only the desired signal from the decomposed light and calculates the tropospheric ozone concentration through the absorption difference caused by ozone.

[0011] At this time, it is preferable to provide a light reflector and a focusing lens for collecting harmonic waves for ozone measurement between the output terminal of the laser light source and the input terminal of the Raman wavelength generator.

[0012] In addition, it is preferable that the output end of the Raman wavelength generator sequentially comprises a collimating lens and a light reflector that form parallel light through a beam that has not passed through the Raman wavelength generator and a beam of wavelength output from the Raman wavelength generator.

[0013] In addition, the above photodetector preferably comprises a pinhole for adjusting the field of view, a lens for converting light passing through the pinhole into parallel light, a dichroic mirror for separating the parallel light into resonant and non-resonant wavelengths, and an interference filter and a wheel for removing atmospheric background signals.

[0014] In addition, it is preferable that the resonant wavelength is 266 nm, and the non-resonant wavelengths are 287 nm and 316 nm. Effects of the invention

[0015] The present invention uses a single laser source to observe the concentration of tropospheric ozone and receives the scattered signal through a single telescope, thereby improving efficiency and reducing the complexity of the system and the instability of optical alignment, which are instability factors of conventional methods that use separate optical systems for transmitting the laser beam and receiving the scattered signal, and enables effective observation of ozone concentration from the lower to the upper layers of the troposphere. Brief explanation of the drawing

[0016] Figure 1 is an explanatory diagram of the observation principle and concentration acquisition processor of a differential absorption lidar (DIAL). FIG. 2 is a graph showing the selected wavelength according to the distance to be calculated in the differential absorption lidar according to an embodiment of the present invention, FIG. 3 is a structural diagram of an optical system transmitting a laser beam and an optical system receiving a scattered signal according to an embodiment of the present invention. FIG. 4 is a block diagram showing a control configuration and connection structure according to an embodiment of the present invention. Figure 5 is a flowchart showing the process of calculating ozone concentration according to an embodiment of the present invention. Specific details for implementing the invention

[0017] The configuration of the laser light transmitting and receiving device of the air pollutant observation lidar of the present invention will be described in detail below with reference to the attached drawings.

[0018] In this invention, Differential Absorption Lidar (DIAL) technology is used, and to observe ozone, a resonant wavelength in which significant absorption occurs in the ultraviolet region ( ) and non-resonant wavelengths where absorption occurs little ( Ozone concentration is determined by investigating the atmosphere and using the backscattered signal difference.

[0019] Specifically, the number of photons that are backscattered and return after a laser is irradiated into the atmosphere is expressed as follows [Equation 1].

[0020]

[0021] Here, : Acquired backscatter signal, : Wavelength of the laser irradiated into the atmosphere, : Laser pulse energy, : Efficiency of a receiving optical system including a photodetector and other optical systems, : Area of ​​the receiving scope, : overlap function, : Energy per unit photon, : Distance resolution, : backscattering coefficient, : Absorption cross-section of the substance to be measured : Number density of the substance to be measured : It is the extinction coefficient caused by air molecules or aerosols.

[0022] In this case, the superposition function is considered to correct for the nonlinearity between the measurement range and the detection period, and is determined by the laser beam divergence and the telescope's field of view. That is, it has a value between 0 and 1 at close range where the overlap between the beam divergence and the telescope's field of view is not complete, and a value of 1 at long range where the overlap is complete. In the present invention, the superposition function has a value of 1 starting from 160m.

[0023] In the case of the DIAL system, the resonance wavelength that is highly absorbed by the measured material ( ) and non-resonant wavelengths adjacent to it but with low absorption ( Since ) is used, two backscattered signals through the following [Equation 2] class Gets.

[0024]

[0025] From the above [Equation 1] and [Equation 2], the number density of the measured substance can be calculated as follows.

[0026]

[0027] Here, And, It represents. Also is the selected resonance wavelength ( ) and non-resonant wavelengths( It represents the difference in absorption cross-sectional area occurring between ) ).

[0028] Representing backscattering and dissipation by air molecules and aerosols in the atmosphere Port The term exhibits significant spatiotemporal variation, and in the case of the troposphere, these variations are largely attributed to aerosols. Therefore, while standard atmospheric data or climate data can be used for the effects of air molecules, the effects of aerosols must be measured and corrected. Based on the corrected results, the number density of the measured substance is reduced to the following [Equation 4], through which the tropospheric ozone concentration can be calculated.

[0029]

[0031] Figure 1 is an explanatory diagram of the observation principle and concentration acquisition processor of a differential absorption lidar (DIAL), schematically illustrating the observation principle and concentration acquisition processor of a differential absorption lidar (DIAL).

[0032] As mentioned earlier, the DIAL system uses two laser beams to utilize the absorption spectrum of a specific molecule. The resonant wavelength (λon) is set to have high absorption on the target, while the other laser beam uses a slightly different non-resonant wavelength (λoff) with low absorption. The absorption cross-section of the molecule being measured is selected such that it is very large at λon and very small at λoff.

[0033] Generally, when a laser beam is irradiated into air, the scattering cross-section of Mie scattering is large, so a Mie scattering signal is received. However, if the gas being measured is distributed, a λon signal smaller than λoff is received.

[0034] Based on the attenuation of these two signals, it is possible to measure the location and concentration of the gas distribution, and distance information to the point where the gas is distributed can be obtained from the time it takes for the laser beam to return.

[0035] In particular, the selection of wavelength is very important in DIAL systems, and the wavelength is chosen by taking into account molecular absorption, absorption interference with other gases, detectors in that wavelength band, and the transmittance and scattering degree in the atmosphere.

[0036] In the case of ozone observed in the present invention, the absorption cross-section is widely distributed according to wavelength with a peak at 250 nm, so an appropriate wavelength is selected according to the measurement distance. For stratospheric ozone with the longest measurement distance, 308 nm is selected as the resonant wavelength and 355 nm as the non-resonant wavelength.

[0037] FIG. 2 is a graph showing the selected wavelength according to the distance to be calculated in the differential absorption lidar according to an embodiment of the present invention, illustrating the selected wavelength.

[0038] To measure ozone in the lower troposphere (below 2 km), a 4th harmonic of a 266 nm Nd:YAG laser was selected as the resonant wavelength, and a 287 nm wavelength was selected as the non-resonant wavelength, which is generated by passing through a Raman shifter into which deuterium (D2) is injected by a laser beam of 266 nm wavelength. In addition, to observe ozone in the higher troposphere (below 4 km), a 287 nm / 316 nm wavelength was selected.

[0039] FIG. 3 is a structural diagram of an optical system that transmits a laser beam and an optical system that receives a scattered signal according to an embodiment of the present invention, and FIG. 4 is a block diagram showing a control configuration and connection structure according to an embodiment of the present invention, illustrating the entire differential absorption lidar system for ozone observation composed of a laser light transmitting and receiving device.

[0040] The laser light transmitter includes a solid-state laser light source (101), a light reflector (102), and a Raman wavelength generator (104). The LiDAR signal receiver includes a reflective telescope (106), a pinhole (107), a lens (108), a dichroic reflector (109), an interference filter and wheel (110), and a light sensor (112). These transmitters and receivers can be controlled via a control module (113), and the series of processes for determining the ozone concentration described above are also performed via the control module (113).

[0041] In an embodiment of the present invention, the fourth harmonic (266 nm), which is an Nd:YAG laser excited by a flash lamp (Flash-Lamp) that is a solid-state laser light source (101), is utilized as a resonance wavelength but is also used as an excitation light source for a Raman wavelength generator (104).

[0042] The fourth harmonic beam generated from the above solid-state laser light source (101) is aligned to be gathered into a Raman wavelength generator (104) by a light reflector (102) and a focusing lens (103), and the Raman generating medium charged in the Raman wavelength generator (104) is deuterium (D2) gas and argon as a buffer gas.

[0043] That is, a beam (266 nm) generated from a solid-state laser light source (101) passes through a Raman wavelength generator, but a part of the beam generates wavelengths of 287 nm and 316 nm by the Raman medium (D2 gas) in the Raman wavelength generator (104), and the remaining beam (266 nm) passes through as is and is irradiated toward the atmosphere.

[0044] Here, through the 4th harmonic, which is the wavelength, the 1st Stokes wavelength of deuterium gas, 287 nm, and the 2nd Stokes wavelength of deuterium gas, 316 nm, are generated. At this time, the efficiency of the Raman wavelength generator (104) depends on the pressure of the charged Raman generating medium and the focal optical path of the excitation light source. That is, a portion of the 4th harmonic (266 nm) oscillated from the solid-state laser light source (101) is used without passing through the Raman wavelength generator (104), and the remainder of the 4th harmonic (266 nm) passes through the Raman wavelength generator (104) to generate the 1st Stokes wavelength, 287 nm, and the 2nd Stokes wavelength, 316 nm, of deuterium gas, thereby producing an output.

[0045] The 266 nm wavelength beam that passes directly through the Raman wavelength generator (104), and the 287 and 316 nm wavelength beams output from the Raman wavelength generator (104) through a Raman medium, pass through a collimating lens (105) to generate parallel light and are irradiated into the atmosphere through a light reflector (102'). The light irradiated into the troposphere from the laser light transmitter is scattered by air molecules or dust, etc., and is received through a reflective telescope (106).

[0046] The signal received from the above-mentioned reflecting telescope (106) passes through a pinhole (107) to adjust the field of view and then passes through a lens (108) to create parallel light. The parallel light that has passed through this passes through a dichroic mirror (109) and is separated by a photodetector provided to separate resonant and non-resonant wavelengths, and then an interference filter and a wheel (110, 110') are used to remove atmospheric background signals to obtain only the wavelength to be observed.

[0047] To obtain a selected wavelength signal, the signal is acquired by being incident on the optical sensor (112, 112') through the condensing lens (111, 111'). Through the acquired signal, the tropospheric ozone concentration can be obtained by calculating the signal according to the measurement distance using the differential absorption method described above.

[0048] In this way, by observing tropospheric ozone with a single laser light source, the system can be implemented at a low cost without the need for expensive optical systems, unlike the complexity of conventional lidar.

[0049] FIG. 5 is a flowchart showing the process of calculating ozone concentration according to an embodiment of the present invention, showing the entire steps for observing tropospheric ozone.

[0050] In the first step (S 10), a portion of the solid-state laser 4th harmonic wave emitted from the laser light source (101) passes through a Raman wavelength generator (104) to generate a new wavelength (287 nm, 316 nm) converted through the existing 4th harmonic wave (266 nm) and a deuterium Raman medium, and the laser light of each wavelength is irradiated into the atmosphere through a light reflector (102').

[0051] Laser light irradiated into the atmosphere is backscattered by air molecules and aerosols present in the atmosphere and is received through a reflective telescope (106). (S 20) At this time, if ozone is present in the atmosphere, a difference in backscattered signals occurs between a resonant wavelength that is heavily absorbed by ozone and a non-resonant wavelength that is less absorbed.

[0052] The lidar signal received through the reflecting telescope (106) is separated into a resonant wavelength and a non-resonant wavelength, and the signals are acquired by the respective optical sensors (112, 112'). (S 30)

[0053] The tropospheric ozone concentration is calculated using the absorption difference caused by ozone, based on the signals received from each channel optical sensor (112, 112'). (S 40)

[0054] The rights of the present invention are not limited to the embodiments described above but are defined by the claims, and it is obvious that a person skilled in the art may make various modifications and adaptations within the scope of the rights described in the claims. Explanation of the symbols

[0055] 101: Laser light source 102: Light reflector 104: Raman wavelength generator 105: Collimating lens 106: Reflecting telescope 108: Pinhole 109: Dichroic reflector 110: Interference filter and wheel 112: Optical sensor 113: Control module

Claims

Claim 1 A laser light transmitting device for observing tropospheric ozone comprises: a laser light source (101) for generating harmonic waves for ozone measurement; a first light reflector (102) and a focusing lens (103) disposed in front of the output end of the laser light source (101) for reflecting and concentrating harmonic waves for ozone measurement and causing them to be incident on a Raman wavelength generator (104); a Raman wavelength generator (104) for receiving harmonic waves for ozone measurement and generating a laser beam of a wavelength including a first Stokes wavelength of 287 nm and a second Stokes wavelength of 316 nm by using only deuterium (D2) gas as the Raman medium; and a 266 nm beam that passes through the Raman wavelength generator (104) without conversion and a 287 nm and 316 nm beam generated by the Raman wavelength generator (104). A transmitter comprising a collimating lens (105) that collimates a beam of a wavelength to create parallel light and a light reflector (102') that changes the path to irradiate the parallel light into the atmosphere, and a beam of 266 nm, which is a harmonic wave for ozone measurement, as a resonant wavelength, and laser beams of 287 nm, which is a first-order Stokes wavelength generated by the Raman wavelength generator, and 316 nm, which is a second-order Stokes wavelength, as non-resonant wavelengths, simultaneously irradiating the atmosphere; a reflective telescope (106) that receives backscattered light irradiated through the transmitter and scattered in the atmosphere, a pinhole (107) for adjusting the field of view of the backscattered light received through the reflective telescope (106), a lens (108) for making the light passing through the pinhole (107) into parallel light, and a device for separating the parallel light into resonant wavelengths and non-resonant wavelengths. A photodecomposer comprising a dichroic mirror (109), an interference filter and wheel (110, 110') for removing atmospheric background signals of each wavelength separated through the dichroic mirror, a condensing lens (111, 111') for condensing light passing through the interference filter and wheel (110, 110'), and a light sensor (112, 112') for detecting light passing through the condensing lens (111, 111');A laser light transmitting and receiving device for a lidar, characterized by comprising: a control module (113) that receives only the desired signal from separated light and calculates the tropospheric ozone concentration through the absorption difference caused by ozone. Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete

Images