CN116663433B - Differential optimization method based on differential absorption spectrometer - Google Patents

Abstract

The invention discloses a differential optimization method based on a differential absorption spectrometer, which belongs to the technical field of electric data processing and is used for carrying out differential optimization of optical data, and comprises the steps of obtaining wavelength and light intensity information of an absorption spectrum through the differential absorption spectrometer, calculating a concentration value of gas according to the absorption light intensity in the spectrum, filtering out a slow change part with low dependence on the wavelength in the spectrum according to the gas extinction effect by using a Bill law, and removing the slow change part and Rayleigh scattering and Mie scattering extinction coefficients to obtain differential optical density only representing gas molecular absorption; and broadening the absorption spectrum lines of the characteristic wavelength bands corresponding to various gases by using the Fogart function, performing least square fitting on the differential optical density and the reference spectrum, and inverting to obtain the final gas concentration value in the current measurement environment. The method improves and optimizes the traditional differential absorption algorithm, improves the precision for solving various gas concentration values, and can adapt to various complex environments.

Description

A differential optimization method based on differential absorption spectrometer

Technical field

The invention discloses a differential optimization method based on a differential absorption spectrometer, which belongs to the technical field of electrical data processing.

Background technique

General instruments can only detect a single gas concentration and cannot detect multiple gas concentrations at the same time. How to detect various pollutant gases in real time and issue alarms according to local air quality standards is the focus of research in the current environment. Differential absorption spectroscopy technology makes up for the shortcomings of traditional instruments and can detect the concentrations of multiple gases at the same time. Differential absorption spectroscopy technology uses solar scattered light or artificially introduced detection light as the light source to obtain the wavelength and intensity of the scattered light. After obtaining the light source information Finally, the differential absorption algorithm is used to invert the concentration information of multiple gases to obtain real-time concentration values of multiple gases. The differential absorption spectrometer has the advantages of being easy to build a platform, retrieving a wide variety of gas concentrations, and can be observed on multiple platforms. For traditional differential absorption technology, the standard absorption cross section is generally obtained from the high-resolution standard absorption cross section in the ultraviolet-visible band in the spectral database. This absorption cross-section data is the gas absorption cross-section of a high-resolution spectrometer at room temperature. The actual situation In order to obtain a variety of different gas concentrations, the absorption cross sections of these gases are different at different temperatures, which will lead to an increase in data errors. In addition, in a low-concentration measurement environment, due to the influence of many environmental conditions such as optical path, concentration, and impurities, the absorption spectrum contains less information about the concentration of the gas to be measured, and the gas concentration value solved by the differential absorption algorithm will produce a large error. , this error may even be above 10%. In view of the shortcomings of the above differential absorption algorithm, the traditional algorithm is optimized and improved so that it can meet the requirements of multiple conditions and high accuracy, and the concentration of various gases to be measured can be more accurately obtained under more complex conditions.

Contents of the invention

The purpose of the present invention is to provide a differential optimization method based on a differential absorption spectrometer to solve the problem of large data errors in differential absorption technology in the existing technology.

A differential optimization method based on differential absorption spectrometer, including:

S1. Obtain the wavelength and light intensity information of the absorption spectrum through a differential absorption spectrometer, calculate the concentration value of the gas from the absorption light intensity in the spectrum, and use Beer-Lambert's law to filter out the slow-changing part of the spectrum based on the gas extinction effect;

S2. Separate the fast-changing and slow-changing parts of the absorption spectrum through digital filtering;

S3. Remove the slow changing part and the Rayleigh scattering and Mi scattering extinction coefficients to obtain the differential optical density that only represents the absorption of gas molecules. ;

S4. Use the Vogt function to broaden the absorption spectral lines of various gases corresponding to the characteristic wavelength range;

S5. After obtaining the effective absorption cross section through data processing, use the effective absorption cross section as the reference spectrum, and perform least squares fitting on the differential optical density and the reference spectrum;

S6. Make a judgment after inverting the gas concentration, and add the catastrophic cycle adaptive crossover operation for optimization based on the genetic algorithm;

S7. Invert to obtain the final gas concentration value in the current measurement environment.

S1 includes:

The relationship between the fast-changing and slow-changing parts of the spectrum and the transmitted light intensity is as follows:

;

In the formula, is the transmitted light intensity of ultraviolet light at a certain wavelength,/> is the incident light intensity of ultraviolet light at a certain wavelength, n is the number of gas species,/> Represents a broadband structural spectrum, that is, the slowly changing part of the spectrum, /> is the differential absorption cross section, that is, the fast-changing part of the spectrum,/> Represents the concentration of the i-th substance at the transmission optical path s,/> and/> are Rayleigh scattering and Mie scattering extinction coefficients respectively.

S2 includes:

High-pass filtering uses a sixth-order polynomial to fit the absorption spectrum within the band:

;

In the formula, is the light intensity after fitting,/> is the coefficient,/> is the wavelength.

S2 includes:

Low-pass filtering uses Savitsky-Gole smoothing to denoise:

;

In the formula, is the smoothed data,/> is the smoothing coefficient,/> is the data before smoothing.

S3 includes:

.

S4 includes:

Voigt function for:

;

in Represents the Doppler spread half-width, /> Indicates gas in the beam/> The absorption line intensity at , according to the influence of temperature on the absorption cross-section, the temperature dependence of F is expressed as:

;

Indicates reference temperature/> The absorption line is strong when is the actual temperature,/> is the reference temperature,/> is the energy of the low-energy state of the molecule,/> is Planck’s constant,/> is the speed of light,/> is Boltzmann’s constant, t represents a variable constant;

x and y are intermediate coefficients:

,/> ;

Represents the center beam of each absorption line, /> Represents pressure broadening half width.

S4 includes:

Doppler spread half-width and pressure broadening half width/> The temperature and pressure dependencies are expressed as:

,/> ;

In the formula, is a dimensionless quantity, taking 1 for symmetrical molecules and 1.5 for asymmetric molecules;/> Indicates actual atmospheric pressure,/> Represents the reference broadening value,/> represents the reference atmospheric pressure, and M represents the gas molecular mass;

According to the actual temperature and atmospheric pressure, compare the reference temperature and atmospheric pressure, calculate and obtain the current high-resolution water vapor absorption cross-section, and then convolve the obtained reference cross-section with the spectrometer instrument function curve to obtain the current effective absorption cross-section of each gas. .

S5 includes:

set up Indicates the first/> Inversion concentration of a gas, based on/> The calculation formula is:

,/> ;

Will The polynomial of is rewritten into matrix form:

;

In the formula, Represents the /> corresponding to the i-th row and m-th column weight,/> ///> corresponding to row i component, thus obtaining the /> Differential optical density of a gas/> and effective absorption cross section/> , and then invert the gas concentration/> .

S6 includes:

S6.1. Use decimal for coding. In coding, each individual contains gene encoding value/> ,/> For the encoded gas concentration, each group consists of 10 random initialization individuals and satisfies:

;

S6.2. Select fitness function for:

;

In the formula, For the first/> sampling points,/> is the number of wavelengths of spectral sampling points,/> is the encoded gas concentration,/> is the differential absorption cross section,/> is the /> in the fitted curve The absorbance value of the sampling point.

S6 includes:

S6.3. Selection operation, calculate the average value of fitness, and select individuals that are smaller than the average value of fitness to enter the next generation;

S6.4. Add catastrophic cycle adaptive crossover operation and define crossover probability for:

;

In the formula, Represents the crossover probability,/> Indicates the number of disasters that have occurred currently,/> Represents a fixed value less than 1,/> Represents an integer used to adjust the range of crossover probability changes, /> Indicates that the population has reached the stage/> generation genetic manipulation;

S6.5. Terminate the operation. When the final concentration value of the individual reaches the required threshold, the optimization algorithm will output the individual with the smallest fitness value as the true value. The error range of the concentration value finally solved by the optimization algorithm is within the threshold range.

Compared with the existing technology, the present invention has the following beneficial effects: by improving and optimizing the traditional differential absorption algorithm, the accuracy of solving various gas concentration values is improved, and at the same time, it can adapt to a variety of complex environments;

In order to adapt to more different environments and at different temperatures, the standard absorption cross-section can be effectively and accurately broadened through the Voigt function to broaden the absorption spectral lines corresponding to the characteristic wavelength ranges of various gases, and then the obtained reference cross-section is compared with the spectrometer instrument function curve Convolution is performed to finally obtain the current effective absorption cross section of each gas, thus reducing the error;

In order to adapt to the environment of small concentration and short optical path, the genetic algorithm is integrated into the final data processing process, and the accuracy of the data is improved by coding, defining fitness function, selection, inheritance, termination, and optimizing the algorithm;

In order to reduce the "premature" phenomenon of the genetic algorithm, the catastrophic cycle adaptive crossover operation is added to the genetic algorithm optimization, and the global search ability of the population mutation is improved by adaptively changing the crossover probability, and the adaptability and accuracy of the algorithm are enhanced.

Description of the drawings

Figure 1 is a technical flow chart of the present invention;

Figure 2 is a digital filtering process diagram;

Figure 3 is a schematic diagram of the effective absorption cross section obtained by the Vogt function.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention are clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

A differential optimization method based on differential absorption spectrometer, including:

S1. Obtain the wavelength and light intensity information of the absorption spectrum through a differential absorption spectrometer. Calculate the gas concentration value from the absorption light intensity in the spectrum. Use Beer-Lambert's law to filter out the low dependence on wavelength in the spectrum based on the gas extinction effect. The slow changing part;

S2. Separate the fast-changing and slow-changing parts of the absorption spectrum through digital filtering;

S3. Remove the slow changing part and the Rayleigh scattering and Mi scattering extinction coefficients to obtain the differential optical density that only represents the absorption of gas molecules. ;

S4. Use the Vogt function to broaden the absorption spectral lines of various gases corresponding to the characteristic wavelength range;

S5. After obtaining the effective absorption cross section through data processing, use the effective absorption cross section as the reference spectrum, and perform least squares fitting on the differential optical density and the reference spectrum;

S6. Make a judgment after inverting the gas concentration. If the measurement is performed in an environment with low gas concentration, the measured gas concentration error will be relatively large. At this time, the catastrophic cycle adaptive crossover operation is added based on the genetic algorithm for optimization;

S7. Invert to obtain the final gas concentration value in the current measurement environment.

S1 includes:

The relationship between the fast-changing and slow-changing parts of the spectrum and the transmitted light intensity is as follows:

;

In the formula, is the transmitted light intensity of ultraviolet light at a certain wavelength,/> is the incident light intensity of ultraviolet light at a certain wavelength, n is the number of gas species,/> Represents a broadband structural spectrum, that is, the slowly changing part of the spectrum, /> is the differential absorption cross section, that is, the fast-changing part of the spectrum,/> Represents the concentration of the i-th substance at the transmission optical path s,/> and/> are Rayleigh scattering and Mie scattering extinction coefficients respectively.

S2 includes:

High-pass filtering uses a sixth-order polynomial to fit the absorption spectrum within the band:

;

In the formula, is the light intensity after fitting,/> is the coefficient,/> is the wavelength.

S2 includes:

Low-pass filtering uses Savitsky-Gole smoothing to denoise:

;

In the formula, is the smoothed data,/> is the smoothing coefficient,/> is the data before smoothing.

S3 includes:

.

S4 includes:

Voigt function for:

;

in Represents the Doppler spread half-width, /> Indicates gas in the beam/> The absorption line intensity at , according to the influence of temperature on the absorption cross-section, the temperature dependence of F is expressed as:

;

Indicates reference temperature/> The absorption line is strong when is the actual temperature,/> is the reference temperature,/> is the energy of the low-energy state of the molecule,/> is Planck’s constant,/> is the speed of light,/> is Boltzmann’s constant, t represents a variable constant;

x and y are intermediate coefficients:

,/> ;

Represents the center beam of each absorption line, /> Represents pressure broadening half width.

S4 includes:

Doppler spread half-width and pressure broadening half width/> The temperature and pressure dependencies are expressed as:

,/> ;

In the formula, is a dimensionless quantity, taking 1 for symmetrical molecules and 1.5 for asymmetric molecules;/> Indicates actual atmospheric pressure,/> Represents the reference broadening value,/> represents the reference atmospheric pressure, and M represents the gas molecular mass;

According to the actual temperature and atmospheric pressure, compare the reference temperature and atmospheric pressure, calculate and obtain the current high-resolution water vapor absorption cross-section, and then convolve the obtained reference cross-section with the spectrometer instrument function curve to obtain the current effective absorption cross-section of each gas. .

S5 includes:

set up Indicates the first/> Inversion concentration of a gas, based on/> The calculation formula is:

,/> ;

Will The polynomial of is rewritten into matrix form:

;

In the formula, Represents the /> corresponding to the i-th row and m-th column weight,/> ///> corresponding to row i component, thus obtaining the /> Differential optical density of a gas/> and effective absorption cross section/> , and then invert the gas concentration/> .

S6 includes:

S6.1. Use decimal for coding. In coding, each individual contains gene encoding value/> ,/> For the encoded gas concentration, each group consists of 10 random initialization individuals and satisfies:

;

S6.2. Select fitness function for:

;

In the formula, For the first/> sampling points,/> is the number of wavelengths of spectral sampling points,/> is the encoded gas concentration,/> is the differential absorption cross section,/> is the /> in the fitted curve The absorbance value of the sampling point.

S6 includes:

S6.3. Selection operation, according to the fitness function, select individuals with smaller fitness values to enter the next generation;

S6.4. Add catastrophic cycle adaptive crossover operation and define crossover probability for:

;

In the formula, Represents the crossover probability,/> Indicates the number of disasters that have occurred currently,/> Represents a fixed value less than 1,/> Represents an integer used to adjust the range of crossover probability changes, /> Indicates that the population has reached the stage/> generation genetic manipulation;

S6.5. Terminate the operation. When the solution concentration value of the last individual reaches the required threshold, the optimization algorithm outputs the individual with the smallest fitness value as the real value. The error range of the concentration value finally solved by the optimization algorithm is within the threshold range.

The technical process of the present invention is shown in Figure 1, which includes obtaining spectral information, high-pass filtering and low-pass filtering, obtaining differential optical density, obtaining effective gas absorption cross-section, least squares fitting, and then directly outputting the normal concentration environment according to different situations. Concentration value, low concentration environment, perform catastrophic genetic algorithm, and output the optimal individual that meets the threshold.

Usually atmospheric scattering includes Rayleigh scattering and Mie scattering. When calculating differential absorption spectroscopy, Rayleigh scattering and Mie scattering are used as absorption processes. The emitted light intensity and received light intensity are obtained by combining Rayleigh scattering, Mie scattering extinction and Lambert-Beer's law. The relationship between. The differential absorption algorithm divides the gas extinction effect into two parts according to its dependence on wavelength: fast changes with high wavelength dependence and slow changes with low wavelength dependence. In spectral analysis, it is necessary to filter out the low wavelength dependence. For the slow-changing part, after filtering out the slow-changing part, the differential optical density that only represents the absorption of gas molecules is obtained. The differential optical density and the reference absorption cross-section of gas molecules are least squares fitted to obtain the concentrations of various gases. Digital filtering is usually used to separate the "fast-changing" and "slow-changing" parts of the absorption spectrum. High-pass digital filtering such as polynomial regression filtering is used to remove the "slow-changing" part of the spectrum, and then low-pass filtering such as triangular filtering is used to reduce the "slow-changing" part of the spectrum. Effect of high frequency noise. The selection of the reference absorption cross section is usually processed directly using the standard cross section. According to the characteristic absorption spectrum peaks of different gases at a certain wavelength in the standard absorption cross section, the corresponding wavelengths are recorded, and the data corresponding to the wavelength in the differential absorption cross section are compared with the standard absorption cross section. The data is fitted by least squares method, and the digital filtering process is shown in Figure 2.

Based on the gas absorption parameters provided by the spectral database, Vogt function fitting was used to broaden the characteristic absorption spectral lines of various gases in the characteristic wavelength range under different temperature conditions. During the fitting, it was found that for a certain gas There are a variety of interfering gases in the corresponding characteristic band. Therefore, in order to improve the accuracy, first select the gas characteristic wavelength band with few interfering gases. Then, if there are other interfering gases in this wavelength band, all interfering gases present in the wavelength range are Perform broadening, and then participate in spectral fitting with the absorption cross section obtained after broadening. For some complex conditions such as low concentration, try to combine and improve the genetic algorithm with the traditional differential absorption algorithm. Define the fitness function according to the gas absorption characteristics, concentration values, etc., and generate the initial data set through the selection, crossover and mutation operations of the genetic algorithm. , and perform iterative optimization on these data, evaluate them according to the fitness function in each generation, select individuals with higher fitness as the next generation population, and perform genetic operations to generate new individuals and repeat the iteration for multiple generations. Operate until the individual with the highest fitness is found, thereby reducing the data error. The Vogt function obtains the effective absorption cross section as shown in Figure 3.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments. The recorded technical solutions may be modified, or some or all of the technical features may be equivalently replaced, but these modifications or substitutions shall not cause the essence of the corresponding technical solutions to depart from the scope of the technical solutions of each embodiment of the present invention.

Claims (6)

1. A differential optimization method based on differential absorption spectrometer, which is characterized by including: S1. Obtain the wavelength and light intensity information of the absorption spectrum through a differential absorption spectrometer, calculate the concentration value of the gas from the absorption light intensity in the spectrum, and use Beer-Lambert's law to filter out the slow-changing part of the spectrum based on the gas extinction effect; S2. Separate the fast-changing and slow-changing parts of the absorption spectrum through digital filtering; S3. Remove the slow changing part and the Rayleigh scattering and Mi scattering extinction coefficients to obtain the differential optical density that only represents the absorption of gas molecules. ; ; In the formula, is the transmitted light intensity of ultraviolet light at a certain wavelength,/> is the incident light intensity of ultraviolet light at a certain wavelength, n is the number of gas species,/> is the differential absorption cross section, that is, the fast-changing part of the spectrum,/> Represents the concentration of the i-th substance at the transmission light path s; S4. Use the Vogt function to broaden the absorption spectral lines of various gases corresponding to the characteristic wavelength range; Voigt function for: ; in Represents the Doppler spread half-width, /> Indicates gas in the beam/> The absorption line intensity at , according to the influence of temperature on the absorption cross-section, the temperature dependence of F is expressed as: ; Indicates reference temperature/> The absorption line is strong when is the actual temperature,/> is the reference temperature,/> is the energy of the low-energy state of the molecule,/> is Planck’s constant,/> is the speed of light,/> is Boltzmann’s constant, t represents a variable constant; x and y are intermediate coefficients: ,/> ; Represents the center beam of each absorption line, /> Represents the pressure broadening half width; Doppler spread half-width and pressure broadening half width/> The temperature and pressure dependencies are expressed as: ,/> ; In the formula, is a dimensionless quantity, taking 1 for symmetrical molecules and 1.5 for asymmetric molecules;/> Indicates actual atmospheric pressure,/> Represents the reference broadening value,/> represents the reference atmospheric pressure, M represents the gas molecular mass; According to the actual temperature and atmospheric pressure, compare the reference temperature and atmospheric pressure, calculate and obtain the current high-resolution water vapor absorption cross-section, and then convolve the obtained reference cross-section with the spectrometer instrument function curve to obtain the current effective absorption cross-section of each gas. ; S5. After obtaining the effective absorption cross section through data processing, use the effective absorption cross section as the reference spectrum, and perform least squares fitting on the differential optical density and the reference spectrum; S6. After inverting the gas concentration, add the catastrophic period adaptive crossover operation for optimization based on the genetic algorithm; S6.1. Use decimal for coding. In coding, each individual contains gene encoding value/> ,/> For the encoded gas concentration, each group consists of 10 random initialization individuals and satisfies: ; S6.2. Select fitness function for: ; In the formula, For the first/> sampling points,/> is the number of wavelengths of spectral sampling points,/> is the encoded gas concentration,/> is the differential absorption cross section,/> is the /> in the fitted curve The absorbance value of each sampling point; S7. Invert to obtain the final gas concentration value in the current measurement environment. 2. A kind of differential optimization method based on differential absorption spectrometer according to claim 1, characterized in that, S1 includes: The relationship between the fast-changing and slow-changing parts of the spectrum and the transmitted light intensity is as follows: ; In the formula, Represents a broadband structural spectrum, that is, the slowly changing part of the spectrum, /> and/> are Rayleigh scattering and Mie scattering extinction coefficients respectively. 3. A kind of differential optimization method based on differential absorption spectrometer according to claim 1, characterized in that, S2 includes: High-pass filtering uses a sixth-order polynomial to fit the absorption spectrum within the band: ; In the formula, is the light intensity after fitting,/> is the coefficient,/> is the wavelength. 4. A kind of differential optimization method based on differential absorption spectrometer according to claim 1, characterized in that, S2 includes: Low-pass filtering uses Savitsky-Gole smoothing to denoise: ; In the formula, is the smoothed data,/> is the smoothing coefficient,/> is the data before smoothing. 5. A kind of differential optimization method based on differential absorption spectrometer according to claim 1, characterized in that, S5 includes: set up Indicates the first/> Inversion concentration of a gas, based on/> The calculation formula is: ,/> ; Will The polynomial of is rewritten into matrix form: ; In the formula, Indicates the effective absorption cross-section component corresponding to the i-th row and m -th column,/> ///> corresponding to row i component, thus obtaining the /> Differential optical density of a gas/> and effective absorption cross section, thereby inverting the gas concentration/> . 6. A kind of differential optimization method based on differential absorption spectrometer according to claim 1, characterized in that, S6 includes: S6.3. Selection operation, calculate the average value of fitness, and select individuals that are smaller than the average value of fitness to enter the next generation; S6.4. Add catastrophic cycle adaptive crossover operation and define crossover probability for: ; In the formula, Represents the crossover probability,/> Indicates the number of disasters that have occurred currently,/> Represents a fixed value less than 1,/> Represents an integer used to adjust the range of crossover probability changes, /> Indicates that the population has reached the stage/> generation genetic manipulation; S6.5. Terminate the operation. When the solution concentration value of the last individual reaches the required threshold, the optimization algorithm will output the individual with a small fitness value as the real value. The error range of the concentration value finally solved by the optimization algorithm is within the threshold range.