A method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar

Abstract

The application discloses a kind of multi-component gas concentration and temperature detection methods based on absorption spectrum laser radar, the detection method is decomposed to a plurality of absorption peaks and background curve to absorption coefficient diagram, background curve can be fitted by basic function, so as to obtain the lorentz function corresponding to absorption peak and the background function corresponding to background curve, these functions are integrated to obtain fitting model;The parameters of the fitting model are simplified;The obtained simplified model is fitted based on sampling point, the relationship between the half-height half-width of main absorption peak in absorption coefficient diagram and temperature is determined, temperature can be inverted based on fitting result, and then the concentration of the measured gas is inverted according to temperature and fitting result;In the process of processing absorption coefficient diagram, temperature is determined synchronously, without measuring temperature by external technical means, improve the real-time performance of temperature measurement, and improve the accuracy of the measured gas concentration measurement.

Description

Technical Field

[0001] The present invention relates to the technical field of gas concentration detection, and in particular to a multi-component gas concentration and temperature detection method based on absorption spectrum laser radar. Background Art

[0002] Atmospheric gas concentration detection has important environmental, health, and scientific significance. First, by detecting gas concentrations in the atmosphere, we can monitor air quality in real time and promptly detect the presence of harmful gases, so that we can take effective measures to protect public health and reduce the harm of air pollution to humans. Second, gas concentration detection is crucial to climate change research. By measuring the concentrations of greenhouse gases such as carbon dioxide (CO2) and methane (CH4), scientists can understand the changing trends of these gases in the atmosphere and predict their impact on the global climate. In addition, gas concentration detection can also be used for industrial emission monitoring, gas management in agricultural production, and air quality assessment in urban planning and management.

[0003] Among them, the detection of greenhouse gases is crucial. Take CO2 as an example. As of 2023, the average global atmospheric CO2 concentration has exceeded 420 ppm, a significant increase from the pre-industrial 280 ppm. Studies have shown that for every 100 ppm increase in CO2 concentration, the Earth's surface temperature will rise by about 1.5°C. Increased CO2 concentrations will lead to global warming, ocean acidification (the pH value of the ocean surface has dropped by about 0.1 since the Industrial Revolution), and biodiversity loss, and will also pose a threat to human health.

[0004] Existing methods for detecting gas concentrations include chemical sensors, electrochemical sensors, infrared spectroscopy, mass spectrometry, and gas chromatography. These technologies are widely used in environmental monitoring, industrial control, and scientific research. Chemical and electrochemical sensors detect gas concentrations through chemical reactions and are suitable for portable devices and real-time monitoring. Infrared spectroscopy, based on the absorption characteristics of gases to infrared light, can detect a wide range of gases. Mass spectrometry and gas chromatography provide highly accurate concentration data by separating and analyzing the different components of a gas sample.

[0005] However, these traditional methods have limitations in terms of spatial resolution and long-distance monitoring. In contrast, the use of LiDAR for gas concentration detection offers significant advantages. LiDAR emits and receives laser beams, interacting with gas molecules in the atmosphere, enabling large-scale, high-precision gas concentration detection. Its advantages lie in its ability to monitor over long distances, three-dimensional imaging, and real-time spatial distribution data. It is particularly suitable for gas monitoring in complex environments, such as industrial emissions, urban air quality monitoring, and greenhouse gas emissions research. Furthermore, the high sensitivity and selectivity of LiDAR technology enable it to accurately measure low-concentration gases, providing a more powerful tool for scientific research and environmental protection.

[0006] LiDAR technology performs well in measuring the concentration of gases such as CO2 in the atmosphere, but existing technologies have difficulty accurately obtaining gas concentration and temperature information simultaneously. Whether using a dual-wavelength differential absorption LiDAR system or a multi-wavelength LiDAR system, converting the CO2 absorption coefficient detected by the LiDAR into CO2 concentration requires known temperature and pressure data. This means that although LiDAR can provide concentration information with high temporal and spatial resolution, the accuracy of concentration measurements will be affected in the absence of synchronized temperature and pressure data. In current detection methods, temperature and pressure data mainly come from radiosondes or models. Using these non-real-time and non-in-situ data for CO2 concentration inversion will lead to errors in CO2 concentration inversion.

[0007] Therefore, there is an urgent need for a method that can synchronously measure gas concentration and temperature during lidar detection to solve the above-mentioned problem of gas concentration inversion error caused by low accuracy of temperature data. Summary of the Invention

[0008] The purpose of the present invention is to overcome the above-mentioned defects or problems existing in the background technology and to provide a multi-component gas concentration and temperature detection method based on absorption spectrum lidar, which can improve the problem of gas concentration inversion error caused by low accuracy of temperature data.

[0009] To achieve the above object, the present invention adopts the following technical solutions:

[0010] Technical solution one: a multi-component gas concentration and temperature detection method based on an absorption spectrum laser radar, the absorption spectrum is drawn after the laser radar emits a detection laser, receives a corresponding echo signal and processes it, the detection method is characterized by comprising: selecting a waveband including multiple gas isotope absorption peaks in the absorption spectrum according to the gas components to be detected, to obtain an absorption coefficient graph; decomposing the absorption coefficient graph to obtain multiple absorption peaks and background curves related to the gas to be detected, and the background curves are suitable for being fitted by a basic function; integrating a fitting model based on the number of decomposed absorption peaks and the shape of the background curve, using multiple Lorentz functions and background functions corresponding to the background curves as units; simplifying the Lorentz function parameters in the fitting model according to the relationship between the parameters of each Lorentz function, and simplifying the background function parameters in the fitting model according to the regression of the background function, to obtain a simplified model; selecting multiple sampling points in the absorption coefficient graph and fitting based on the sampling points by the simplified model; determining the relationship between the half-height half-width of the main absorption peak in the absorption coefficient graph and the temperature, inverting the temperature based on the fitting result, and inversely obtaining the concentration of the gas to be detected accordingly; taking each inversion result as input, simplifying the fitting model again, and fitting again based on the simplified model after simplification, multiple iterations until the fitting result is stable, and inverting the temperature based on the stable fitting result, and referring to the temperature to invert the concentration of the gas to be detected.

[0011] Technical solution two based on technical solution one: the basic function used to establish the background function corresponding to the background curve includes but is not limited to a linear function and a quadratic function.

[0012] Technical solution three based on technical solution one: the simplification of the parameters in the fitting model includes: setting the center wave number in the Lorentz function as a constant; establishing the relationship between the half-height half-width in the Lorentz function corresponding to different gas absorption peaks and the temperature, determining the ratio relationship of the half-height half-width in each Lorentz function based on this, and expressing the half-height half-width of other Lorentz functions based on the half-height half-width of the Lorentz function of the main absorption peak and referring to the ratio relationship; according to the ratio relationship of the areas of the Lorentz functions of the same gas absorption peak, expressing the areas of other absorption peaks belonging to the same gas based on the area of one of the Lorentz functions and referring to the ratio relationship, and expressing the areas of the Lorentz functions of the absorption peaks of other gases in the same way.

[0013] Technical solution four based on technical solution one: the sampling points selected in the absorption coefficient graph are suitable for describing the absorption peaks of the gas to be detected and the shape of the background curve, and the sampling points include but are not limited to: the points at the center wave numbers of each absorption peak after decomposition, the points at the half-height half-width corresponding positions of each absorption peak after decomposition, the points at the highest positions of the absorption coefficient graph, and the points at the two wings of the absorption coefficient graph.

[0014] Technical solution five based on technical solution one: when fitting according to the sampling points, a reference point is determined in the absorption coefficient map, and the unit optical depths of other sampling points are calculated based on the reference point.

[0015] Technical solution 6 based on technical solution 1: When fitting according to the sampling points, the initial value of the simplified model is calculated based on the environmental parameters during laser detection, and the initial value is combined with the sampling points for fitting.

[0016] Technical Solution 7 based on Technical Solution 1: When the concentration and temperature of the gas to be measured are obtained by inversion, the gas concentration is inverted using the area of ​​the Lorentz function of each decomposed absorption peak.

[0017] From the above description of the present invention, it can be seen that compared with the prior art, the present invention has the following beneficial effects:

[0018] The present invention provides a multi-component gas concentration and temperature detection method based on absorption spectrum laser radar. The detection method decomposes the absorption coefficient graph to obtain multiple absorption peaks and background curves. The principle of decomposition is to enable the background curve to be fitted by a basic function, thereby obtaining a Lorentz function corresponding to the absorption peak and a background function corresponding to the background curve. These functions are integrated to obtain a fitting model with high precision. The parameters of the fitting model are then simplified to reduce the parameters that need to be fitted, thereby reducing the fitting error. The simplified model is then fitted based on the sampling points, and the relationship between the half-height half-width of the main absorption peak in the absorption coefficient graph and the temperature is determined. Based on the fitting result, the temperature can be inverted, and then the concentration of the gas to be measured is inverted according to the temperature and the fitting result. After that, the accuracy of the inversion result is improved through multiple iterative inversions. In the process of processing the absorption coefficient graph, the temperature is synchronously determined, and there is no need to measure the temperature by external technical means, thereby improving the real-time performance of the temperature measurement. The concentration of the gas to be measured can be accurately calculated based on the determined temperature, thereby improving the accuracy of the concentration measurement of the gas to be measured. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0020] Figure 1 A flow chart of a detection method provided by an embodiment of the present invention;

[0021] Figure 2 6360cm -1Absorption coefficient diagram (a) in the embodiment using the wavelength band as an example, and background value diagrams after removing S1, S2, S3 (b), removing S1, S2, S3, S4 (c), and removing S1, S2, S3, S4, S5 (d);

[0022] Figure 3 6360cm -1 Schematic diagram of the effects of CO2 content (a), H2O content (b), temperature (c), and pressure (d) on the background value after removing five peaks in the embodiment using the wavelength band as an example;

[0023] Figure 4 6360cm -1 Schematic diagram of the effects of CO2 content (a) and temperature (b) on the half-width at half-maximum of the absorption peak in the embodiment using the wavelength band as an example;

[0024] Figure 5 6360cm -1 Schematic diagram of the effect of temperature on the half-height / half-width ratios of absorption peaks S2 and S1 (a), S3 and S1 (b), S4 and S1 (c), and S5 and S1 (d) in the embodiment using the wavelength band as an example;

[0025] Figure 6 6360cm -1 Schematic diagram of the effect of temperature on the ratio of the area A of the absorption peaks S3 to S2 (a), S4 to S1 (b), and S5 to S1 (c) in the embodiment using the wavelength band as an example;

[0026] Figure 7 6360cm -1 Schematic diagram of the fitting results (a) and fitting residuals (b) of the fitting model in the noise-free case in the embodiment taking the band as an example;

[0027] Figure 8 6360cm -1 Schematic diagram of the deviation of CO2 (a), T (b), and H2O (c) simultaneously inverted by the CO2 spectral radar based on the fitting model in the noise-free embodiment using the wavelength band as an example. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be regarded as excluding other embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0029] The terms "comprise", "have" and any variations thereof are intended to cover "include but not limited to" when used in this specification, the claims and the accompanying drawings.

[0030] Embodiments

[0031] The embodiment of the present application provides a multi-component gas concentration and temperature detection method based on an absorption spectrum laser radar, which can detect the concentration of multiple gases in the atmosphere through absorption spectrum of the laser radar, wherein the absorption spectrum is drawn after receiving and processing the corresponding echo signal after the laser radar emits a detection laser, and the laser radar used is a multi-wavelength laser radar, which can simultaneously use multiple detection lasers in a wide wavelength range to measure the concentration of multiple gases in the atmosphere.

[0032] Reference Figure 1 It shows the general process of the detection method provided by the embodiment of the present application. Specifically, the detection method comprises:

[0033] Step one: according to the gas component to be detected, selecting a waveband including multiple gas isotope absorption peaks in the absorption spectrum to obtain an absorption coefficient graph;

[0034] Step two: decomposing the absorption coefficient graph to obtain multiple absorption peaks and background curves related to the gas to be detected, and the background curve is suitable for fitting by a basic function;

[0035] Step three: according to the number of decomposed absorption peaks and the form of the background curve, integrating a fitting model with multiple Lorentz functions and background functions corresponding to the background curve as units;

[0036] Step four: simplifying the Lorentz function parameters in the fitting model according to the relationship between the parameters of each Lorentz function, and simultaneously simplifying the background function parameters in the fitting model according to the regression condition of the background function to obtain a simplified model;

[0037] Step five: selecting multiple sampling points in the absorption coefficient graph, and fitting based on the sampling points through the simplified model;

[0038] Step six: determining the relationship between the half-height half-width of the main absorption peak in the absorption coefficient graph and the temperature, inverting the temperature based on the fitting result, and inversely obtaining the concentration of the gas to be detected according to the temperature;

[0039] Step seven: taking each inversion result as input, simplifying the fitting model again, and fitting again according to the simplified model after the simplification, and iterating multiple times until the fitting result is stable, and inverting the temperature based on the stable fitting result, and referring to the temperature to invert the concentration of the gas to be detected.

[0040] Wherein, in step three, when establishing the background function corresponding to the background curve, the basic functions used include but are not limited to a linear function and a quadratic function.

[0041] In step 4, the simplification of the parameters in the fitting model includes: setting the central wave number in the Lorentz function to a constant; establishing the relationship between the half-width at half maximum and the temperature in the Lorentz function corresponding to the absorption peaks of different gases, thereby determining the ratio relationship of the half-width at half maximum in each Lorentz function, and using the half-width at half maximum of the Lorentz function of the main absorption peak as the basis, referring to the ratio relationship to represent the half-width at half maximum of other Lorentz functions; based on the ratio relationship of the areas in the Lorentz function of the same gas absorption peak, using the area of ​​one of the Lorentz functions as the basis, referring to the ratio relationship to represent the areas of the Lorentz functions of other absorption peaks belonging to the same gas, and representing the areas of the Lorentz functions of the absorption peaks of other gases in the same manner. Wherein, the above-mentioned half-width at half maximum refers to half of the half-width at half maximum of the absorption peak.

[0042] In step five, the sampling points selected in the absorption coefficient diagram are suitable for describing the absorption peak of the gas to be measured and the shape of the background curve. The selected sampling points include but are not limited to: points at the central wavenumber of each absorption peak after decomposition, points at the corresponding positions of the half-height and half-width of each absorption peak after decomposition, points at the highest position of the absorption coefficient diagram, and points on both wings of the absorption coefficient diagram.

[0043] Meanwhile, in step 5, when fitting based on the sampling points, a reference point is determined in the absorption coefficient map, and the unit optical depths of the other sampling points are calculated based on the reference point. Furthermore, when fitting based on the sampling points, initial values ​​of the simplified model are calculated based on environmental parameters during laser detection, and fitting is performed using these initial values ​​in conjunction with the sampling points.

[0044] In step six, when the concentration and temperature of the gas to be measured are obtained by inversion, the gas concentration is inverted using the area of ​​the Lorentzian function of each decomposed absorption peak.

[0045] The multi-component gas concentration detection method based on the laser radar absorption spectrum provided above first decomposes the absorption coefficient graph to obtain multiple absorption peaks and background curves. The principle of decomposition is to enable the background curve to be fitted by the basic function, thereby obtaining the Lorentz function corresponding to the absorption peak and the background function corresponding to the background curve. These functions are integrated to obtain a fitting model with high accuracy. The parameters of the fitting model are then simplified to reduce the parameters that need to be fitted, thereby reducing the fitting error. The simplified model is then fitted based on the sampling points and the relationship between the half-height and half-width of the main absorption peak in the absorption coefficient graph and the temperature is determined. The temperature can be inverted based on the fitting result, and the concentration of the gas to be measured is then inverted based on the temperature and the fitting result. The accuracy of the inversion result is then improved through multiple iterative inversions. In the process of processing the absorption coefficient graph, the temperature is synchronously determined, and there is no need to measure the temperature through external technical means, which improves the real-time performance of the temperature measurement. The concentration of the gas to be measured can be accurately calculated based on the determined temperature, thereby improving the accuracy of the concentration measurement of the gas to be measured.

[0046] Specifically, the following will take the detection of carbon dioxide and water in the atmosphere as an example to illustrate the above-mentioned multi-component gas concentration detection method based on absorption spectrum lidar. It should be understood that this embodiment is exemplary and should not be construed as limiting the present invention.

[0047] Reference Figure 2 (a) of Figure 1, in this embodiment, 6360 cm -1 The band is taken as an example. This band has obvious CO2 and HDO absorption peaks and can be used to simultaneously measure atmospheric CO2, H2O and temperature.

[0048] Reference Figure 2 (a) shows that 6360 cm -1 Absorption coefficient diagram of the band, marked at 6359.967cm -1 The CO2 absorption peak is S1, located at 6359.748 cm -1 The first absorption peak of HDO is S2, located at 6360.278 cm -1 The second absorption peak of HDO is S3, located at 6360.113 cm -1 The CO2 absorption peak is S4, located at 6359.864 cm -1 The CO2 absorption peak is S5.

[0049] Reference Figure 2 In Figure (d), after subtracting the absorption peaks of S1 to S5, the background curve can be represented by a quadratic function in the basis function, that is, the background function can be a(xb) 2 +c. For comparison, refer to Figure 2 Figure (b) of the drawings of Figure 2 Figure (a) of the drawings minus the profile at the absorption peaks S1, S2, S3, with further reference to Figure 2 Figure (c) of the drawings, which shows Figure 2 Figure (b) of the drawings minus the profile at the absorption peak S4.

[0050] Therefore, for the present example, the model of the absorption coefficient can be expressed as:

[0051] F(x) = f1 + f2 + f3 + f4 + f5 + a(x - b) 2 + c (1)

[0052] where the Lorentzian function is expressed as:

[0053]

[0054] In formula (2), A is the area of the Lorentzian peak (cm -2 ), ω L is the half-height half-width of the Lorentzian function (cm -1 ), x c is the central wave number of the Lorentzian function in the environmental conditions (cm -1 ).

[0055] The relationship of the above parameters can be explained by the following formula:

[0056]

[0057] P self = P - X - abybdance (6)

[0058]

[0059] In the above formula, x0 represents the central wave number in vacuum (cm -1 ), P represents the atmospheric pressure (Pa), P shift represents the pressure shift of the spectral line position (cm -1 / atm), T represents the environmental temperature (K), T0 represents the standard temperature 296 K, n air is the temperature-dependent coefficient of pressure broadening (dimensionless), γ air is the environmental broadening (cm -1 / atm), γ self is the self-broadening (cm -1 / atm), P self represents the target gas partial pressure (Pa), S(T) represents the transition intensity of the spectral line at the environmental temperature T (cm / molecule), S(T0) represents the transition intensity of the spectral line at the standard temperature 296 K (cm / molecule), kb represents the Boltzmann constant, X represents the content of the target gas in the atmosphere, abundance is the abundance of the target isotope in nature, c2 represents the second radiation constant, h represents the Planck constant, c represents the speed of light, Q(T0) represents the absorbing gas partition function at standard temperature 296K (hitran download data), Q(T) represents the absorbing gas partition function at temperature T, and E″ represents the low-energy state energy of the transition (cm -1 ).

[0060] According to formula (1) and formula (2), the parameters that need to be fitted in this model include: the unknown number involved in the Lorentz function, the absorption peak center wave number x c , absorption peak area A, half-height half-width ω L There are 15 unknowns in total, 3 of which are background functions, for a total of 18. Since too many unknowns will affect the accuracy and speed of fitting, it is necessary to simplify the unknowns.

[0061] See also Figure 3 In this embodiment, the above background values ​​are analyzed by different CO2 content (a), H2O content (b), temperature (c), and pressure (d) on the background value after removing the five peaks. Figure 3 It can be seen that the background value function under different conditions conforms to the quadratic equation a(xb) 2 +c results, and fitting the background values ​​in these cases, it was found that b returned to 6359.97, so b was fixed to a constant of 6359.97. Figure 3 Take the Fitted result in (a) as an example. That is, in this embodiment, the background function requires two unknowns to be fitted.

[0062] For this embodiment, it can be seen from (3) that the central wave number x c It is related to temperature and pressure. Calculation shows that when the temperature changes by 1K, the central wave number will change by about 1.5×10 -5 cm -1 When the pressure changes by 1 hPa, the central wave number changes by about 5.7×10 -8 cm -1 , however, taking the absorption peak S1 as an example, its half-height half-width ω L About 0.08cm -1 , temperature and pressure have an influence on the absorption peak center wave number x c The impact of 10 -5 and 10 -8 The order of magnitude is negligible relative to the width of the absorption peak. That is, in this embodiment, the central wave numbers of the five Lorentz functions can be set to constants.

[0063] For this embodiment, the half-height half-width ω LThe calculation of ω is shown in formula (4), L This parameter is mainly affected by temperature rather than gas content, so it can be approximately considered that the ω of HDO peaks S2, S3 and CO2 peaks S1, S4, S5 L There is also a connection between them. If the ω of CO2 absorption peak S1 is known L With the other four absorption peaks S2, S3, S4, S5ω L The ratio of S1 can be used to calculate the ω L The ω of the other four peaks L In which the temperature and pressure are brought into parameters close to the environment, P self is the partial pressure of the target gas, and a parameter close to the CO2 content in the atmosphere is substituted as the initial value for calculation. When the initial temperature changes, ω L The change in the ratio between Figure 5 As shown: For every 1K increase, S 2ωL / S 1ωL The ratio decreases by about 3.97×10 -4 、S 3ωL / S 1ωL The ratio decreases by about 3.90×10 -4 、S 4ωL / S 1ωL The ratio increased by about 3.85×10 -5 、S 5ωL / S 1ωL The ratio is fixed at 0.9865. It can be seen that the ω between each peak L The ratio of this parameter can be considered to be fixed. And the gas content changes, the ω of the five peaks L Basically unchanged. That is, for this embodiment, ω L Only the CO2 absorption peak S1 ω is needed L One unknown number can be used to calculate the ω of the five peaks. L Express them all.

[0064] For this embodiment, the calculation of area A is shown in (5)(6)(7)(8). It can be seen from formula (5) that area A is related to gas concentration and spectral line intensity S(T). For the same gas with the same concentration, A is only related to S(T). From this, the ratio between the areas of HDO peaks S2 and S3, and the ratio between the areas of CO2 peaks S1, S4, and S5 can be obtained. For CO2 absorption peak S1 and HDO absorption peak S2, the initial value of the absorption peak area can also be obtained using (5)(6)(7)(8). It can be seen from formula (5) that for the same gas, the absorption peak area is only related to the spectral line intensity of the absorption peak, while it can be seen from formula (8) that the ratio between different peaks of the same gas is only related to the parameters of the absorption peak itself and the temperature. When the ambient temperature changes, the change in the ratio between the peak areas is as follows: Figure 6As shown: When the temperature rises by 1K, S 3A / S 2A The ratio decreases by about 1.67×10 -3 、

[0065] S 4A / S 1A The ratio increased by about 1.59×10 -5 、S 5A / S 1A The ratio increased by about 6.40×10 -6 . These values ​​are approximately 0.001 times the original order of magnitude of the ratio, and the error is negligible. Therefore, the ratio of the areas between the peaks can be used to approximate each other. In the fitting, the ratio of the peak areas can be determined by determining the temperature. Therefore, if there is the area of ​​the HDO absorption peak S2 and the ratio between the areas of the absorption peaks S2 and S3, the area of ​​the HDO absorption peak S3 can be approximately expressed, and the same is true for the CO2 absorption peak. Therefore, taking A of peaks S1 and S2 as unknowns, the areas of S3, S4, and S5 can be expressed by the relationship between the peaks. Therefore, for this embodiment, the parameter area can be fully expressed with the two unknowns of the areas of the absorption peaks S1 and S2.

[0066] After the above simplification process, the original fitting model is simplified to obtain a simplified model. The unknown parameters in the simplified model are reduced from 18 to 5, namely: the area A1 of the strongest CO2 absorption peak S1 in this band, the area A2 of the strongest HDO absorption peak S2 in this band, the half-height half-width ω of the strongest absorption peak S1 in this band L , background value parameters a and c.

[0067] After obtaining the simplified model, the simplified model can be fitted using the sampling points in the absorption coefficient graph.

[0068] Specifically, in this embodiment, 30 sampling points were selected, including points at the central wavenumbers of five strong absorption peaks, points at the corresponding positions of the half-height and half-width of the strong absorption peaks, the highest point of the absorption coefficient diagram, points with weaker absorption on both wings of the absorption coefficient diagram, etc. The selected points can describe the shape and characteristics of the absorption peak.

[0069] The lidar equation is expressed as (9)(10):

[0070]

[0071] In formula (9), R is the distance, N s is the number of returned photons, E is the pulse energy (J), x i is the laser wave number (cm -1 ), R represents the distance (m), h is Planck's constant, η0 is the optical efficiency of the transmitted signal (%), η qis the quantum efficiency (%), A t is the area of ​​the telescope (m 2 ), O(R) represents the geometric overlap factor at distance R, c is the speed of light, τ is the pulse width (s), β is the Mie volume backscattering coefficient (m -1 ), T r is the transmittance function, which can be expressed as:

[0072]

[0073] In formula (10), α a is the aerosol extinction coefficient (m -1 ), including the effects of scattering and absorption, α s is the molecular extinction coefficient, denoted as α s =α+α m , where α is the absorption coefficient of the gas being studied, α m Represents the extinction coefficient of other molecules.

[0074] In this embodiment, the reference point is set to 6360.6 cm -1 The calculation of unit optical depth UOD is shown in (3):

[0075]

[0076] x0 is the wave number of the reference point, α(x i ,R) and α(x0,R) are the wave number x i and the atmospheric absorption coefficient at x0.

[0077] Before fitting, an initial value needs to be set in advance. In this embodiment, the initial value is obtained by first substituting (4)-(8) according to the ambient temperature, pressure, CO2 content and H2O content during the detection process, and then fitting is performed using (1) as the model function to obtain the area A1 of the absorption peak S1, the area A2 of the absorption peak S2, and the half-height half-width ω of the absorption peak S1. L The fitting results refer to Figure 7 Figure (a) in the figure, Figure 7 Figure (b) is the residual of the fitting result. It can be seen that the deviation of the fitting result is better.

[0078] For this embodiment, it can be seen from formula (4) that T, P and P self Joint decision L Among them, P can use atmospheric model data, which has a small deviation. Next, we will analyze T and P self Right L First, P self Right l The effect of ω is approximately l 10 of its own order of magnitude-5 ~10 -4 The first half of formula (4) is γ air (P0,T0)(PP self ) represents the effect of the pressure of other gases in the atmosphere on the broadening, and the latter part γ self (P0,T0)P self Indicates the effect of the partial pressure of the target gas itself on the broadening. Figure 4 As shown in (a), the temperature is fixed at 297K and the pressure is 101325Pa. The CO2 content is changed from 350ppm to 550ppm, and ω is obtained. L Schematic diagram of the effect of CO2, it can be found that ω L Only 5×10 -6 cm -1 In addition, the H2O content was changed from 0 to 4%, and the ω of the absorption peak S2 was analyzed. L As a result of the change, when the H2O content changes from 1.0% to 2.0%, ω L Only 9×10 -7 cm -1 . And ω L The order of magnitude itself is 10 -2 cm -1 , P self Right L The effect of ω is approximately L 10 of its own order of magnitude -5 ~10 -4 , it can be seen that ω L Small impact from changes in gas content.

[0079] Compared with the effect of gas, ω l It is more sensitive to temperature changes. According to formula (4), the half-height half-width of the CO2 absorption peak S1 at 223K to 324K can be calculated, and the half-height half-width of S1 can be fitted. l The relationship curve with temperature. Figure 4 In (b), ω is plotted when P is 101325 Pa, T is 297 K, and CO2 is 450 ppm, 400 ppm, and 350 ppm, respectively. L The curves change with temperature, but because the influence of gas content is too small, the three curves are basically overlapped. L The change is about 2.5×10 -4 cm -1 , it can be seen that ω L is more sensitive to temperature changes than to changes in gas content. Therefore, ω L The change of is basically not affected by the gas content, it is mainly determined by the temperature and can be used Figure 4 (b) ω LThe temperature is inverted based on the relationship between the temperature and the

[0080] From formula (5), we can see that area A is directly related to the gas content, so the gas concentration can be inverted using area A.

[0081] Because the initial conditions differ from the actual conditions, it's difficult to get accurate results in a single fit. Therefore, iteration is necessary. The calculated CO2, temperature, and H2O values ​​are used as the initial values ​​for the next fit. The resulting area and half-height half-width are then fitted again, and CO2, temperature, and H2O are calculated. This cycle repeats until stability is achieved.

[0082] In this embodiment, the CO2 spectrum radar in different noise-free conditions simultaneously inverts the systematic errors of CO2(a), T(b), and H2O(c) based on the fitting model provided in this embodiment. Figure 8 As shown in Figure 2, it was found that the systematic error of the fitting model in measuring CO2 was less than 0.1ppm under the environmental conditions of CO2 content of 350-550ppm. Figure 8 (a) shows that the influence of ambient temperature on temperature deviation is also very small. Under the ambient temperature of 250-310K, the temperature deviation is less than 0.11K. The point with the smallest error is at 270K. At this time, the system deviation of temperature can reach 0.004K. On both sides of this point, the absolute value tends to increase linearly, as shown below. Figure 8 (b) shows that the absolute value of the H2O system deviation in the fitting model shows a trend of gradual increase with the increase of H2O content in the environment, but its maximum value is still less than 0.02, as shown below Figure 8 (c) shown.

[0083] The above description and embodiments are intended to explain the scope of protection of the present invention, but do not constitute a limitation thereto. Modifications, equivalent substitutions, or other improvements to the embodiments of the present invention or portions thereof that can be obtained by a person of ordinary skill in the art through logical analysis, reasoning, or limited experimentation based on the teachings of the present invention or the above embodiments, combined with common knowledge, ordinary technical knowledge in the field, and / or prior art, should all be included within the scope of protection of the present invention.

Claims

1. A method for detecting the concentration and temperature of a multi-component gas based on an absorption spectrum laser radar. The absorption spectrum is plotted by the laser radar emitting a detection laser and then receiving the corresponding echo signal. The detection method is characterized by comprising: According to the gas composition to be measured, a band including absorption peaks of multiple gas isotopes is selected in the absorption spectrum to obtain an absorption coefficient graph; Decomposing the absorption coefficient graph to obtain a plurality of absorption peaks and a background curve associated with the gas to be measured, wherein the background curve is suitable for fitting by a basis function; According to the number of decomposed absorption peaks and the shape of the background curve, a fitting model is formed by integrating multiple Lorentz functions and background functions corresponding to the background curve as units; According to the relationship between the parameters of each Lorentz function, the parameters of the Lorentz function in the fitting model are simplified. At the same time, according to the regression of the background function, the parameters of the background function in the fitting model are simplified to obtain a simplified model. Selecting a plurality of sampling points in the absorption coefficient graph, and performing fitting based on the sampling points using the simplified model; Determine the relationship between the half-width at half-height of the main absorption peak in the absorption coefficient diagram and temperature, invert the temperature based on the fitting result, and then invert the temperature to obtain the concentration of the gas to be measured; Taking each inversion result as input, the fitting model is simplified again, and fitting is performed again based on the simplified model, and multiple iterations are performed until the fitting result is stable. The temperature is inverted with the stable fitting result, and the concentration of the gas to be measured is inverted with reference to the temperature.

2. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, characterized in that: When establishing the background function corresponding to the background curve, the basic functions used include but are not limited to linear functions and quadratic functions.

3. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, characterized in that: The simplification of parameters in the fitting model includes: Set the central wave number in the Lorentz function to a constant; The relationship between the half-width at half-height and the temperature in the Lorentzian function corresponding to the absorption peaks of different gases is established, and the ratio of the half-width at half-height in each Lorentzian function is determined based on the half-width at half-height of the Lorentzian function of the main absorption peak. The half-width at half-maximum of other Lorentzian functions is expressed with reference to the ratio relationship; According to the ratio relationship of the areas of the Lorentz functions of the absorption peaks of the same gas, the areas of the Lorentz functions of other absorption peaks belonging to the same gas are expressed with reference to the ratio relationship based on the area of ​​one of the Lorentz functions, and the areas of the Lorentz functions of the absorption peaks of other gases are expressed in the same way.

4. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, wherein: The sampling points selected in the absorption coefficient diagram are suitable for describing the absorption peak of the gas to be measured and the shape of the background curve. The selected sampling points include but are not limited to: points at the central wavenumber of each absorption peak after decomposition, points at the corresponding positions of the half-height and half-width of each absorption peak after decomposition, points at the highest position of the absorption coefficient diagram, and points on both wings of the absorption coefficient diagram.

5. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, characterized in that: When fitting is performed according to the sampling points, a reference point is determined in the absorption coefficient map, and the unit optical depths of other sampling points are calculated based on the reference point.

6. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, characterized in that: When fitting is performed according to the sampling points, initial values ​​of the simplified model are calculated based on the environmental parameters during laser detection, and the fitting is performed using the initial values ​​in combination with the sampling points.

7. The method for detecting multi-component gas concentration and temperature based on absorption spectrum laser radar according to claim 1, characterized in that: When the concentration and temperature of the gas to be measured are obtained by inversion, the gas concentration is inverted using the area of ​​the Lorentz function of each decomposed absorption peak.

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