CN109085133B - Off-axis integral cavity atmosphere CH based on real-time reflectivity correction4Concentration measuring device and measuring method thereof - Google Patents
Off-axis integral cavity atmosphere CH based on real-time reflectivity correction4Concentration measuring device and measuring method thereof Download PDFInfo
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Abstract
The invention discloses a device for measuring the concentration of off-axis integral cavity atmosphere CH4 based on real-time reflectivity correction, and also discloses the off-axis integral cavity atmosphere CH based on real-time reflectivity correction4A measuring method of a concentration measuring device. The invention adopts an off-axis integral cavity output spectrum method based on real-time reflectivity correction to carry out atmosphere CH4Measurement of concentration, the method does not require the use of a known concentration of CH prior to testing4The standard gas calibrates the high reflection mirror reflectivity of the off-axis integration cavity, and calibrates the high reflection mirror reflectivity in real time in an actual measurement environment, so that the reflectivity measurement deviation caused by the change of the test environment can be avoided, the gas concentration measurement deviation caused by the change of the reflectivity is reduced, and the system measurement stability is improved4And (5) monitoring the concentration in real time.
Description
Technical Field
The invention relates to an off-axis integral cavity atmosphere CH based on real-time reflectivity correction4Concentration measuring device, and also relates to a measuring method of the measuring device, belonging to the technical field of optical measurement.
Background
CH4Is one of the main gases responsible for the greenhouse effect, although at very low concentrations in the atmosphere (about 1.8ppmv), its effect on the greenhouse effect is CO225 times of the above and its concentration is increasing at a rate of 1.1% per yearPlays an important role in global warming. Rapid, real-time and accurate monitoring of trace CH in low-altitude atmosphere4The content has important significance for analyzing atmospheric methane sources, reducing methane emission and reducing global warming tracks. With the benefit of the development of laser light sources, various high-sensitivity spectroscopic methods have been applied to atmosphere CH with maturity4And gas measurement, including cavity ring-down spectroscopy (CRDS), off-axis integral cavity output spectroscopy (OA-ICOS), etc. Among them, OA-ICOS has extremely high sensitivity and robustness, compared with CRDS, the anti-interference ability is stronger, and the method is more suitable for external field measurement, thereby being widely applied to atmosphere CH4Detection and analysis.
Atmosphere CH detection by existing off-axis integral cavity measurement system4The reflectivity of the high-reflectivity mirror needs to be calibrated, and the currently common calibration mode is to use CH with known concentration before testing4The standard gas calibrates the reflectivity. However, due to the components of the air to be measured and CH in the actual field environment4The components of the standard gas are different and may change at any time, the reflectivity measurement value obtained completely according to the calibration mode has certain deviation, and the measurement deviation of the reflectivity can cause CH4The concentration measurements yield deviations. More seriously, when the testing environment changes, the reflectivity changes, and CH is adopted4The reflectivity calibrated by the standard gas is a fixed value, which causes the stability of the measurement of the system to be reduced. On the other hand, due to the atmosphere CH4At concentrations of the order of ppmv, the order of CH4The standard gas is complex to prepare and has certain error in concentration, and CH4The calibration gas cost is high, and the calibration process is complicated. Thus, a method was developed that does not require the use of a known concentration of CH prior to testing4Off-axis integrating cavity atmosphere CH with reflectivity calibrated by standard gas and capable of correcting reflectivity in real time4The concentration measuring apparatus and the measuring method thereof are particularly important.
Disclosure of Invention
The purpose of the invention is as follows: the invention aims to solve the technical problem of providing an off-axis integral cavity atmosphere CH based on real-time reflectivity correction4And (4) a concentration measuring device.
The invention also solvesThe technical problem is to provide the off-axis integral cavity atmosphere CH based on real-time reflectivity correction4The method for measuring concentration of gas in atmosphere CH can reduce the deviation of gas concentration measurement caused by reflectivity change, improve the measurement stability of the system, and is suitable for measuring atmosphere CH4And (5) monitoring the concentration in real time.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
off-axis integral cavity atmosphere CH based on real-time reflectivity correction4The concentration measuring device comprises two detection light paths and a signal processing module, wherein optical signals of the two detection light paths are transmitted to the signal processing module by corresponding photoelectric detectors respectively for processing; the first detection light path sequentially comprises a function generator I, a laser controller I, DFB laser I, an optical collimator, a resonant cavity, a focusing lens and a photoelectric detector I, and air to be detected is filled in the resonant cavity; the function generator I generates a signal to the laser controller I, the laser controller I controls the DFB laser I to modulate the laser wavelength with a high-frequency sinusoidal signal while scanning an absorption spectral line, laser emitted by the DFB laser I is collimated by the optical collimator and then enters the resonant cavity in an off-axis manner, the incident laser is absorbed by air to be detected, then the incident laser comes out of the resonant cavity, is focused by the focusing lens and then receives the signal by the photoelectric detector I, and the photoelectric detector I converts the acquired optical signal into an electric signal and transmits the electric signal to the signal processing module; the second detection light path sequentially comprises a function generator II, a laser controller II, a DFB laser II, a reference absorption pool and a photoelectric detector II, wherein the reference absorption pool is filled with air to be detected; function generator II generates a signal and gives laser controller II, laser controller II controls DFB laser II and modulates laser wavelength with high-frequency sinusoidal signal when scanning absorption spectral line, the laser that DFB laser II sent is transmitted to the entrance port of reference absorption cell by optic fibre, after the air absorption that awaits measuring in the reference absorption cell, come out from the reference absorption cell and receive the signal by photoelectric detector II, photoelectric detector II converts the light signal who gathers into the signal transmission to the signal processing module in.
The air distribution assembly consists of a premixing pipe, a flow controller and an air pump; one end of the premixing pipe is connected with the air inlet end, and the other end of the premixing pipe is respectively connected with the resonant cavity and the air inlet of the reference absorption pool; the gas outlets of the resonant cavity and the reference absorption pool are respectively connected with a gas extraction pump through connecting pipelines, and flow controllers are arranged on the connecting pipelines.
Wherein, the DFB laser I is 1653.7nmDFB laser, and the DFB laser II is 1391.7nmDFB laser.
The premixing tube sends air to be detected into the resonant cavity and the reference absorption pool respectively for detection.
The off-axis integral cavity atmosphere CH based on real-time reflectivity correction4The measuring method of the concentration measuring device comprises the following steps:
step 1, respectively modulating laser wavelength by a high-frequency sinusoidal signal while scanning absorption spectrum lines by a DFB laser I and a DFB laser II in two detection light paths, respectively receiving signals by a photoelectric detector I and a photoelectric detector II after emitted laser passes through a resonant cavity and a reference absorption cell, respectively measuring by the photoelectric detector I to obtain a background light intensity signal and a transmission light intensity signal of the resonant cavity, and measuring by the photoelectric detector II to obtain a background light intensity signal and a transmission light intensity signal of the reference absorption cell;
step 2, performing phase-locked filtering processing on the background light intensity signal and the transmission light intensity signal of the reference absorption pool obtained in the step 1 to obtain a corresponding background-buckled first harmonic normalized second harmonic signal, and extracting H of the reference absorption pool2A measurement of O absorption peak height;
and 3, obtaining different H by combining an HITRAN2016 database according to the known atmospheric temperature, pressure, reference absorption cell length and the measured reference absorption cell background light intensity signal2The light intensity signal of the transmission of the simulation reference absorption cell corresponding to the O concentration is processed by phase-locked filtering to obtain the corresponding background-buckled first harmonic normalized second harmonic signal, and H is extracted2Height value of O absorption peak, establishing different H2O concentration and H2Substituting the database of the height value of the O absorption peak into the H of the reference absorption cell in the step 22Obtaining real-time H from the height measurement of the O absorption peak2A measurement of O concentration;
step 4, performing phase-locked filtering processing on the background light intensity signal and the transmission light intensity signal of the resonant cavity to obtain a corresponding background-buckled first harmonic normalized second harmonic signal, and extracting H of the resonant cavity2Measurement of O absorption Peak height and CH4Absorption peak height measurements;
step 5, according to the known atmospheric temperature, pressure intensity, resonant cavity length and real-time H2Combining the measured O concentration value and the measured background light intensity signal of the resonant cavity with an HITRAN2016 database to obtain the transmission light intensity signals of the simulated resonant cavity corresponding to different reflectivities, performing phase-locked filtering to obtain the corresponding background-buckled first harmonic normalized second harmonic signal, and extracting H2Height of O absorption peak, establishing different reflectivities and H2Substituting the database of the height value of the O absorption peak into the H of the resonant cavity in the step 42Obtaining a real-time reflectivity measurement value by using the O absorption peak height measurement value;
and 6, obtaining different CH according to the known atmospheric temperature, pressure intensity, resonant cavity length, real-time reflectivity measurement value and measured resonant cavity background light intensity signal by combining with an HITRAN2016 database4The light intensity signal of the transmission of the simulation resonant cavity corresponding to the concentration is processed by phase-locked filtering to obtain a corresponding background-deducting first harmonic normalized second harmonic signal, and CH is extracted4Absorption peak height values, establishing different CH4Concentration and CH4Substituting the absorption peak height value database into the CH of the resonant cavity in the step 44Obtaining real-time CH from the measured value of the height of the absorption peak4Concentration measurements.
Has the advantages that: the invention adopts an off-axis integral cavity output spectrum method based on real-time reflectivity correction to carry out atmosphere CH4Measurement of concentration, the method does not require the use of a known concentration of CH prior to testing4The standard gas calibrates the high reflection mirror reflectivity of the off-axis integration cavity, and calibrates the high reflection mirror reflectivity in real time in an actual measurement environment, so that the reflectivity measurement deviation caused by the change of the test environment can be avoided, the gas concentration measurement deviation caused by the change of the reflectivity is reduced, and the system measurement stability is improved4And (5) monitoring the concentration in real time.
Drawings
FIG. 1 is an off-axis integrator chamber atmosphere CH based on real-time reflectivity correction according to the present invention4A system schematic of a concentration measurement device;
FIG. 2 is an off-axis integrator chamber atmosphere CH based on real-time reflectivity correction in accordance with the present invention4A flow chart of a concentration measurement method;
FIG. 3 shows the measurement of the atmosphere CH using the measurement device of the present invention4Results of concentration measurements.
Detailed Description
The technical solution of the present invention is further explained with reference to the accompanying drawings and specific embodiments.
As shown in FIG. 1, the off-axis integrator cavity atmosphere CH based on real-time reflectivity correction of the present invention4The concentration measuring device comprises two detection light paths and a signal processing module 4, wherein optical signals of the two detection light paths are transmitted to the signal processing module 4 by corresponding photoelectric detectors respectively for processing; the first path of detection light path sequentially comprises a function generator I8, a laser controller I9, a DFB laser I10, an optical collimator 11, a resonant cavity 12, a focusing lens 13 and a photoelectric detector I18, wherein air to be detected is filled in the resonant cavity 12; the function generator I8 generates a signal to the laser controller I9, the laser controller I9 controls the DFB laser I10 to modulate the laser wavelength with a high-frequency sine signal while scanning an absorption spectrum line, the laser emitted by the DFB laser I10 is collimated by the optical collimator 11 and then enters the resonant cavity 12 in an off-axis manner, the incident laser is absorbed by air to be detected and then comes out of the resonant cavity 12 and is focused by the focusing lens 13 and then is received by the photoelectric detector I18, and the photoelectric detector I18 converts the acquired optical signal into an electric signal and transmits the electric signal to the signal processing module 4; the second detection light path sequentially comprises a function generator II5, a laser controller II6, a DFB laser II7, a reference absorption pool 17 and a photoelectric detector II3, and air to be detected is filled in the reference absorption pool 17; the function generator II5 generates signals to the laser controller II6, the laser controller II6 controls the DFB laser II7 to scan absorption spectrum lines and modulate laser wavelength with high-frequency sine signals, laser emitted by the DFB laser II7 is transmitted to an entrance port of the reference absorption cell 17 through an optical fiber and passes through the reference absorption cellAfter the air to be detected in the receiving pool 17 is absorbed, the air comes out of the reference absorbing pool 17 and is received by the photoelectric detector II3, and the photoelectric detector II3 converts the acquired optical signal into an electric signal and transmits the electric signal to the signal processing module 4; wherein, DFB laser I10 is 1653.7nmDFB laser, DFB laser II7 is 1391.7nmDFB laser; 1653.7nmDFB laser can scan 6046.95cm simultaneously-1Is located at CH4And absorption line of 6047.79cm-1At H2Absorption spectrum line of O, and synchronously realizing the calibration of reflectivity and CH4Measuring the concentration; in the atmosphere H2Higher concentration of O, selected from H2O is 7185.60cm-1The absorption spectral line can realize real-time monitoring of the concentration under the condition of a short absorption optical path. The detection light source employed in the actual measurement is not limited to the 1653.7nm DFB laser and the 1391.7nm DFB laser.
Off-axis integral cavity atmosphere CH based on real-time reflectivity correction4The concentration measuring device also comprises an air distribution assembly, wherein the air distribution assembly consists of a premixing pipe 14, a flow controller 15 and an air suction pump 16; one end of the premixing pipe 14 is connected with an external air inlet end, and the other end of the premixing pipe 14 is respectively connected with the resonant cavity 12 and an air inlet of the reference absorption pool 17; the air outlets of the resonant cavity 14 and the reference absorption pool 17 are respectively connected with an air suction pump 16 through a connecting pipeline 2, flow controllers 15 are respectively arranged on the connecting pipeline 2, air to be detected in the environment is sucked by the air suction pump 16, the air flow controllers 15 control the air suction flow, and the air to be detected respectively enters the resonant cavity 12 and the reference absorption pool 17 for detection after being mixed by the premixing pipe 14.
The function generator II5 generates signals to the laser controller II6 to control the DFB laser II7 to modulate the laser wavelength with a high-frequency sinusoidal signal while scanning the absorption spectrum line, the emitted laser is transmitted to the entrance port of the reference absorption cell 17 through an optical fiber, and the laser is absorbed by the air to be detected, comes out of the reference absorption cell 17 and receives the signals through the photoelectric detector II 3; meanwhile, the function generator I8 generates a signal to the laser controller I9 to control the DFB laser I10 to modulate the laser wavelength with a high-frequency sinusoidal signal while scanning an absorption spectrum line, the emitted laser passes through the optical collimator 11 and then enters the resonant cavity 12 in an off-axis manner, is absorbed by air to be detected, then comes out of the resonant cavity 12 and is focused by the focusing lens 13, the signal is received by the photoelectric detector I18, and the two photoelectric detectors convert the two optical signals into electric signals which are transmitted to the signal processing module 4 for processing.
As shown in FIG. 2, the off-axis integrator cavity atmosphere CH based on real-time reflectivity correction of the present invention4The concentration measuring method comprises the following steps:
step 1, controlling the central temperature and current of a 1391.7nmDFB laser by a laser controller II6 to ensure that the light-emitting central wavelength of the laser is lambda1(7185.60cm-1) vicinity, function generator II5 output frequency fsHas a superposition frequency of fmThe high-frequency sine modulation signal tunes the output wavelength of the DFB laser, the output laser is transmitted to the reference absorption cell 17 by the optical fiber, and the photodetectors II3 respectively measure the reference absorption cell 17N2Background light intensity signal
And transmitted light intensity signal
Simultaneously, the central temperature and the current of the 1653.7nmDFB laser are controlled by a laser controller I9, so that the light-emitting central wavelength of the laser is lambda2(6047.35cm-1) Nearby, the function generator I8 outputs the frequency fsHas a superposition frequency of fmThe high-frequency sine modulation signal tunes the output wavelength of the DFB laser, the output laser is collimated by the optical collimator 11 and then enters the resonant cavity 12 in an off-axis manner, and the photoelectric detectors I18 respectively measure the resonant cavity 12N2Background light intensity signal
And a transmitted light intensity signal IM(v)；λ1Is H2O wavelength of the measuring line, λ2Is CH4Measuring spectral line (6046.95 cm)-1) And nearby H2O absorption line (6047.79 cm)-1) An intermediate wavelength of (d);
step 2, the background light intensity of the reference absorption cell 17 is informedNumber (C)
And transmitted light intensity signal
Performing phase-locked filtering processing to obtain corresponding background-buckled first harmonic normalized second harmonic signal
Extracting H of reference absorption cell2Measurement of height of O absorption Peak
In the formula (1), the reaction mixture is,
for the convolution symbols, F is the filter function, t is time, FmIn order to modulate the frequency of the signal,
respectively the intensity of background light
The X and Y directional components of the corresponding first and second harmonics;
respectively the intensity of transmitted light
The X and Y directional components of the corresponding first and second harmonics;
respectively the intensity of transmitted light
And background light intensity
The absolute value of the corresponding first harmonic signal,
is the intensity of transmitted light
Normalizing the second harmonic signal by the corresponding background-deducting first harmonic;
step 3, according to Beer-Lambert law, the absorption rate k (v)1) Is shown as
Wherein p is the gas pressure,
is the atmosphere H2O concentration, L is the length of the reference absorption cell, S (T) is the spectral line intensity of the absorption spectral line at the temperature T, T is the gas temperature (obtained by real-time monitoring of a temperature and humidity measuring instrument HMT 333), phi (v)1) The linear function of the absorption spectrum line is described by adopting a Voigt linear form, and the spectrum line parameters in the linear function are provided by a HITRAN2016 database;
the transmission light intensity of the simulated reference absorption cell can be obtained by the formula (2)
Comprises the following steps:
establishing different H2Concentration of O
Corresponding simulated reference absorption cell transmitted light intensity
Will be provided with
And
performing the same phase-locked filtering processing in the step 2 to obtain the corresponding background-buckled first harmonic normalized second harmonic signal
Extracting to obtain H2Height value of O absorption peak
Establishing
And
database of (2), substitution
Obtaining real-time H2O concentration measurements
Step 4, the background light intensity signal of the resonant cavity is processed
And a transmitted light intensity signal IM(v) Performing the same phase-locked filtering processing in the step 2 to obtain the corresponding background-buckled first harmonic normalized second harmonic signal
Extracting the H2O absorption peak height measurement of the resonant cavity
And CH4 measurement of absorption Peak height
Step 5, the basic theory of the off-axis integral cavity shows that the background light intensity signal of the resonant cavity
And a transmitted light intensity signal IM(v) The relationship of (1) is:
wherein R is the reflectivity of the resonant cavity high reflecting mirror, the upper is the resonant cavity length (same as the reference absorption cell length), alpha (v) is the gas absorption coefficient, and alpha (v) is expressed as
α(ν)＝p·x·S(T)·φ(v) (5)
Wherein x is gas concentration, and the simulated resonant cavity transmitted light intensity signal I can be obtained from the formulas (4) and (5)S(v) Comprises the following steps:
establishing different reflectivities RSCorresponding simulation resonant cavity transmitted light intensity signal IS(v) Is shown byS(v) And
performing the same phase-locked filtering processing as the step 2 to obtain the corresponding phase-locked filterBackground-deducting first harmonic normalized second harmonic signal
Extracting to obtain H2Height value of O absorption peak
Establishment of RSAnd
database of (2), substitution
Obtaining a real-time reflectivity measurement Rr；
Step 6, establishing different CH4 concentrations from equation (6)
Corresponding simulation resonant cavity transmitted light intensity signal IS(v) Is shown byS(v) And
performing the same phase-locked filtering processing in the step 2 to obtain the corresponding background-buckled first harmonic normalized second harmonic signal
Extracted CH4 absorption peak height value
Establishing
And
database of (2), substitution
Obtaining CH4 concentration measurements
Atmospheric real-time H2The O concentration measurement results are shown in FIG. 3 (a), the scanning frequency is 50Hz, and H is given after 500-cycle averaging2O concentration measurement, atmospheric H within 600s test time2The concentration of O slowly fluctuates within +/-0.5%, and the real-time reflectivity R is obtained by calculationrThe measurement results are shown in FIG. 3 (b), and the average reflectance Rf0.99501 with a standard deviation of 1.2X 10-4Calculated real-time CH in atmosphere4The results of concentration measurement are shown in (c) of FIG. 3, atmosphere CH4The mean concentration measurement was 1.821ppmv with a standard deviation of 0.024ppmv, i.e. a relative deviation of 1.31% and a time resolution of 10 s. While using the average reflectivity RfCalculated CH in atmosphere4Concentration results are also in FIG. 3(c), atmospheric CH obtained4The mean concentration measurement was 1.820ppmv with a standard deviation of 0.052ppmv, i.e. a relative deviation of 2.86%. From the above results, it can be seen that the real-time reflectance R is usedrCalculated CH4The concentration result has small relative deviation and better stability, effectively reduces the measurement deviation caused by the change of reflectivity, and the measuring device can realize the atmosphere CH4The concentration is measured quickly, in real time and stably.
Claims (1)
1. Off-axis integral cavity atmosphere CH based on real-time reflectivity correction4A method for measuring concentration, characterized in that,
the measuring device comprises two detection light paths and a signal processing module, wherein optical signals of the two detection light paths are transmitted to the signal processing module by corresponding photoelectric detectors respectively for processing; the first detection light path sequentially comprises a function generator I, a laser controller I, DFB laser I, an optical collimator, a resonant cavity, a focusing lens and a photoelectric detector I; the function generator I generates a signal to the laser controller I, the laser controller I controls the DFB laser I to modulate the laser wavelength with a high-frequency sinusoidal signal while scanning an absorption spectral line, laser emitted by the DFB laser I is collimated by the optical collimator and then enters the resonant cavity in an off-axis manner, the incident laser is absorbed by air to be detected in the resonant cavity, then the laser comes out of the resonant cavity and is focused by the focusing lens, and then the signal is received by the photoelectric detector I, and the photoelectric detector I converts the acquired optical signal into an electric signal and transmits the electric signal to the signal processing module; the second detection light path sequentially comprises a function generator II, a laser controller II, a DFB laser II, a reference absorption cell and a photoelectric detector II; the function generator II generates a signal to the laser controller II, the laser controller II controls the DFB laser II to scan an absorption spectral line and simultaneously modulate the laser wavelength with a high-frequency sinusoidal signal, the laser emitted by the DFB laser II is transmitted to an entrance port of a reference absorption cell through an optical fiber, the laser is absorbed by air to be detected in the reference absorption cell, the laser comes out of the reference absorption cell and is received by the photoelectric detector II, and the photoelectric detector II converts the acquired optical signal into an electric signal and transmits the electric signal to the signal processing module; the measuring device also comprises a gas distribution assembly, wherein the gas distribution assembly consists of a premixing pipe, a flow controller and an air pump; the premixing tube is used for respectively sending air to be detected into the resonant cavity and the reference absorption pool for detection, one end of the premixing tube is connected with the air inlet end, and the other end of the premixing tube is respectively connected with the air inlets of the resonant cavity and the reference absorption pool; the gas outlets of the resonant cavity and the reference absorption pool are respectively connected with a gas extraction pump through connecting pipelines, and flow controllers are arranged on the connecting pipelines;
the measuring method comprises the following steps:
step 1, respectively modulating laser wavelength by a high-frequency sinusoidal signal while scanning absorption spectrum lines by a DFB laser I and a DFB laser II in two detection light paths, respectively receiving signals by a photoelectric detector I and a photoelectric detector II after emitted laser passes through a resonant cavity and a reference absorption cell, respectively measuring by the photoelectric detector I to obtain a background light intensity signal and a transmission light intensity signal of the resonant cavity, and measuring by the photoelectric detector II to obtain a background light intensity signal and a transmission light intensity signal of the reference absorption cell; the center wavelength of the light emitted by the DFB laser II is 7185.60cm-1The center wavelength of the light emitted by the DFB laser I is 6047.35cm-1Nearby, 7185.60cm-1Is H2O wavelength of the measurement line, 6047.35cm-1Is CH4Measurement line 6046.95cm-1And nearby H2O measurement line 6047.79cm-1An intermediate wavelength of (d);
step 2, performing phase-locked filtering processing on the background light intensity signal and the transmission light intensity signal of the reference absorption pool obtained in the step 1 to obtain a corresponding second harmonic signal of first harmonic normalization of the background, and extracting H of the reference absorption pool2A measurement of O absorption peak height;
and 3, obtaining different H by combining an HITRAN2016 database according to the known atmospheric temperature, pressure, reference absorption cell length and the measured reference absorption cell background light intensity signal2The light intensity signal of the transmission of the simulation reference absorption cell corresponding to the O concentration is processed by phase-locked filtering to obtain a second harmonic signal of the first harmonic normalization of the corresponding background, and H is extracted2Height value of O absorption peak, establishing different H2O concentration and H2Substituting the database of the height value of the O absorption peak into the H of the reference absorption cell in the step 22Obtaining real-time H from the height measurement of the O absorption peak2A measurement of O concentration;
step 4, performing phase-locked filtering processing on the background light intensity signal and the transmission light intensity signal of the resonant cavity to obtain a corresponding second harmonic signal of primary harmonic normalization of the background, and extracting H of the resonant cavity2Measurement of O absorption Peak height and CH4Absorption peak height measurements;
step 5, according to the known atmospheric temperature, pressure intensity, resonant cavity length and real-time H2The measured value of the O concentration and the measured background light intensity signal of the resonant cavity are combined with an HITRAN2016 database to obtain the transmission light intensity signals of the simulated resonant cavity corresponding to different reflectivities, the transmission light intensity signals of the simulated resonant cavity corresponding to different reflectivities are processed by phase-locked filtering to obtain the first harmonic normalized second harmonic signal of the corresponding background, and H is extracted2Height of O absorption peak, establishing different reflectivities and H2Substituting the database of the height value of the O absorption peak into the H of the resonant cavity in the step 42Obtaining a real-time reflectivity measurement value by using the O absorption peak height measurement value;
step 6, combining HITRAN2016 data according to the known atmospheric temperature, pressure, resonant cavity length, real-time reflectivity measurement value and measured resonant cavity background light intensity signalPool of different CH4The light intensity signal of the transmission of the simulation resonant cavity corresponding to the concentration is processed by phase-locked filtering to obtain a second harmonic signal of the first harmonic normalization corresponding to the background, and CH is extracted4Absorption peak height values, establishing different CH4Concentration and CH4Substituting the absorption peak height value database into the CH of the resonant cavity in the step 44Obtaining real-time CH from the measured value of the height of the absorption peak4Concentration measurements.
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