CN102879772A - Broadening correcting method of atmospheric pressure for differential absorption atmospheric CO2 laser radar - Google Patents

Abstract

The invention relates to a broadening correcting method of atmospheric pressure for differential absorption atmospheric CO2 laser radar. The broadening correcting method is characterized in that a correction formula which is sensitive to the wavelength is adopted to calculate Lorentz full width at half maximum (FWHM); considering both the broadening factor and the independence of temperature related index, the problem of a mixture ratio dynamic value of high altitude CO2 is solved by adopting two ideas of direct value taking and iteration solution; and the ratio x, namely differential absorption laser radar equation concentration solution, of CO2 molecule concentration and volume is transformed. With the adoption of the broadening correcting method, the uncertainty of taking values of the classical algorithm is abandoned to the maximum extent so as to avoid bringing new errors; meanwhile according to the experimental scene demands, the method of specifically adopting value taking solution or iteration has the advantage of flexibility and has good application prospect and great development potential in the field of differential absorption laser radar for detecting atmospheric CO2.

Description

A kind of Difference Absorption Atmospheric CO 2Laser radar atmospheric pressure broadening modification method

Technical field

The present invention relates to the atmospheric optics field, relate in particular to a kind of Difference Absorption Atmospheric CO ₂Laser radar atmospheric pressure broadening modification method.

Background technology

CO ₂As the greenhouse gases principal ingredient global climate is had important influence, the variation of its concentration can produce material impact to global climate.By to CO ₂The Real-Time Monitoring of concentration can independently, in time obtain comprehensive, reliable regional CO ₂Remittance multidate information in source is tackled growing carbon emission stress problems.DIAL is being surveyed CO ₂The aspect has huge advantage, is the desirable detecting devices of its vertical profile distribution of observation, and continuous time and spatial observation can be provided, and obtains higher spatial and temporal resolution.For DIAL, available signal shows as and is detected atmospheric substance to the absorption of laser beam energy.In order to get rid of the impact of other factors, in DIAL, usually adopt the very little wavelength of two bundle difference as the Emission Lasers bundle simultaneously.Wherein the wavelength of beam of laser is selected in the center of CO2 absorption peak, makes it be subject to absorption maximum, is called λ _On, the wavelength of another Shu Jiguang is absorbing the paddy place, and dampen out possibility that it is subject to is little, is called λ _OffBy measuring the Atmospheric CO that increases with highly ₂The variation that absorbs comes inverting CO ₂CONCENTRATION DISTRIBUTION.

Yet, utilizing DIAL to survey CO ₂During concentration, atmospheric pressure broadening has very important material impact to it, and the correction of atmospheric pressure broadening is for CO ₂The retrieving concentration of laser radar is extremely important.

Height R place thickness is Δ R=R ₂-R ₁Atmospheric envelope in (R namely is positioned at the higher height R of atmospheric envelope ₂The height R lower with atmospheric envelope ₁Between intermediate altitude), the CO that DIAL is surveyed ₂Concentration equation can show as following form:

$\left(1\right),N_g=\frac{1}{2[{\mathrm{\σ}}_g\left({\mathrm{\λ}}_{\mathrm{on}}\right)-{\mathrm{\σ}}_g\left({\mathrm{\λ}}_{\mathrm{off}}\right)](R_2-R_1)}\ln \frac{\mathrm{Ps}({\mathrm{\λ}}_{\mathrm{off}},R_2)\mathrm{Ps}({\mathrm{\λ}}_{\mathrm{on}},R_1)}{\mathrm{Ps}({\mathrm{\λ}}_{\mathrm{on}},R_2)\mathrm{Ps}({\mathrm{\λ}}_{\mathrm{off}},R_1)}$

Ng represents CO in the formula ₂The height of density distributes, σ _g(λ) representative is detected the absorption cross section of component, is the sensitivity function of wavelength X, wherein σ _g(λ _On) be wavelength X _OnSensitivity function, σ _g(λ _Off) be wavelength X o _FfSensitivity function; Ps () represents echoed signal intensity, Ps (λ _Off, R ₂) expression employing wavelength X _OffSurvey height R ₂The echoed signal intensity that the place obtains, Ps (λ _On, R ₁) expression employing wavelength X _OnSurvey height R ₁The echoed signal intensity that the place obtains, Ps (λ _On, R ₂) expression employing wavelength X _OnSurvey height R ₂The echoed signal intensity that the place obtains, Ps (λ _Off, R ₁) expression employing wavelength X _OffSurvey height R ₁The echoed signal intensity that the place obtains.By following formula as seen, the density that is detected component is relevant with the difference of the absorption cross section at the ratio of two passage echoed signals and two wavelength places.σ _gValue (λ) is relevant with Lorentz full width at half maximum (FWHM), and the variation of atmospheric pressure and temperature can directly cause the variation of FWHM, is called pressure broadening, and its spectral line shape is provided by the Lorentz profile.Along with the increase of height, the fluctuation that the synthermal existence of pressure is larger causes the Lorentz profile to change to some extent, must revise it, i.e. atmospheric pressure broadening correction is to obtaining higher precision.

The classical way that adopts in the world at present is the theories of atmosphere radiation, finds the solution FWHM, solves the pressure broadening problem, and following computing method are arranged:

${\mathrm{\γ}}_L(P,T)={\mathrm{\γ}}_0\frac{P}{P_0}{\left(\frac{T}{T_0}\right)}^n---\left(2\right)$

γ in the formula _L(P, T) represents the Lorentz full width at half maximum, and P is pressure data, and T is temperature data, γ ₀Standard pressure P ₀(1.013KPa) with standard temperature T ₀Halfwidth in the time of (273K), n are the temperature correlation index.

Its limitation is the uncertainty on the value.For CO ₂Molecule, γ ₀Change obviously with spectral line, general value is 0.07cm in the world ^-1Temperature correlation index n changes in the scope of 0.5-1, gets to be called classical value at 0.5 o'clock.Ambiguity on this value has been brought huge error to inversion result.

The art not yet has relevant solution to occur.

Summary of the invention

The modification method that the purpose of this invention is to provide the broadening of a kind of comparatively accurately atmospheric pressure.

For achieving the above object, the present invention adopts following technical scheme:

A kind of Difference Absorption Atmospheric CO ₂Laser radar atmospheric pressure broadening modification method is characterized in that, may further comprise the steps: step 1, and adopt following formula to calculate the Lorentz full width at half maximum,

${\mathrm{\γ}}_L(P,T,\mathrm{\λ})=P\×\{b_L(\mathrm{air},\mathrm{\λ})\×(1-\mathrm{\χ})\×{\left[\frac{T_0}{T}\right]}^{n_a\left(\mathrm{\λ}\right)}+b_L({\mathrm{CO}}_2,\mathrm{\λ})\×\mathrm{\χ}\×{\left[\frac{T_0}{T}\right]}^{n_{C{O}_2}\left(\mathrm{\λ}\right)}\}---\left(3\right)$

In the formula, γ _L(P, T, λ) represents the Lorentz full width at half maximum, and P is pressure data, and λ is wavelength, and T is temperature data, T ₀Standard temperature, b _L(air, λ) is the atmospheric pressure broadening coefficient of Accurate Measurement, b _L(CO ₂, λ) be CO ₂Gas from the broadening coefficient, χ is CO ₂Gas is with the volume ratio of air, n _a(λ),

Value is respectively atmosphere and CO ₂The gas temperature index of correlation;

Step 2 judges whether to satisfy the iteration termination condition, is process ends then, otherwise enters step 3;

Step 3 according to step 1 gained Lorentz full width at half maximum, obtains CO by the DIAL equation ₂CONCENTRATION DISTRIBUTION, this result directly show with molecular conecentration C, transform by following formula and obtain CO ₂The concentration of gas and volume ratio χ

$\left(4\right),C=\frac{{6.02\×10}^{20}}{22.4}\×\mathrm{\χ}\×\frac{T_0}{T}\×\frac{P}{P_0}$

In the formula, C is CO in every cc of air ₂The molecule number;

Return step 1, according to the new CO that calculates ₂The concentration of gas and volume ratio χ recomputate the Lorentz full width at half maximum.

And the iteration termination condition adopts default iterations in the step 2.

And, in the step 1, according to CO ₂Gas adopts formula (3) to calculate the Lorentz full width at half maximum with the default initial value of the volume ratio χ of air, and default iterations is made as 1.

And, in the step 1, CO ₂Gas is 0.04% with the default initial value of the volume ratio χ of air.

The application has proposed a kind of new modification method of pressure broadening, realize to the full extent the correspondence of spectral line data with FWHM under the status of criterion and temperature correlation index n, adopted corresponding halfwidth γ according to choose (the present invention adopts 1.57 mum wavelengths) of experiment wavelength ₀With temperature correlation index n, science, rationally more, inversion result is more accurate.Simultaneously can solve the same problem that other wavelength (spectral line) data face.The present invention has the following advantages and good effect:

1) the classical uncertainty that is corrected on the value of having forgone has been avoided bringing into of new error;

2) the clear and definite relation of the FWHM co-wavelength under the status of criterion;

3) according to the actual scene demand, the method that adopts respectively the band value to find the solution with iteration has dirigibility.Band value derivation speed is fast, can realize testing the real-time demonstration of inversion result; The method of iteration can increase substantially inversion accuracy.

4) measurement of new correct algorithm parameter is carried out in the wide spectrum scope, has reference value for other (such as 2 μ m) laser radars;

Embodiment

Describe by the following examples technical solution of the present invention in detail.

A kind of Difference Absorption Atmospheric CO of embodiment ₂Laser radar atmospheric pressure broadening modification method can adopt computer software to calculate and realize automatically operation, may further comprise the steps:

Step 1 adopts following formula to calculate the Lorentz full width at half maximum,

${\mathrm{\γ}}_L(P,T,\mathrm{\λ})=P\×\{b_L(\mathrm{air},\mathrm{\λ})\×(1-\mathrm{\χ})\×{\left[\frac{T_0}{T}\right]}^{n_a\left(\mathrm{\λ}\right)}+b_L({\mathrm{CO}}_2,\mathrm{\λ})\×\mathrm{\χ}\×{\left[\frac{T_0}{T}\right]}^{n_{C{O}_2}\left(\mathrm{\λ}\right)}\}---\left(3\right)$

In the formula, γ _L(P, T, λ) represents the Lorentz full width at half maximum, and P is pressure data, and λ is wavelength, and T is temperature data, T ₀Standard temperature, b _L(air, λ) is the atmospheric pressure broadening coefficient of Accurate Measurement, b _L(CO ₂, λ) be CO ₂Gas from the broadening coefficient, χ is CO ₂Gas is with the volume ratio of air, n _a(λ), Value is respectively atmosphere and CO ₂The gas temperature index of correlation.

The Difference Absorption Atmospheric CO that the present invention proposes ₂Laser radar atmospheric pressure broadening modification method, at first clear and definite employing formula (3) carries out the calculating of Lorentz full width at half maximum.This formula need to the temperature, the pressure profile that highly distribute, relate to altogether 8 parameters, wherein 5 parameter b _L(air, λ), b _L(CO ₂, λ), χ, n _a(λ),

The susceptibility of FWHM to wavelength that has been that increase newly, concrete, clear and definite is more complicated, accurate.Correct the broadening coefficient b in the formula _L(air), b _L(CO ₂) and temperature correlation index n _a,

λ is closely related with laser emission wavelength, and is corresponding one by one.

According to CO ₂Absorption line, and consider that corresponding steam disturbs should minimum, the present invention advises adopting 1.57 mum wavelengths, i.e. Difference Absorption 1.57 μ m Atmospheric CO ₂Laser radar is selected the wavelength X of 1572.018nm _OnAs wavelength, 1572.150nm is as wavelength X _OffAccording to λ _OnOr λ _OffCorresponding parameter is calculated with formula (3), can obtain λ _OnOr λ _OffThe absorption cross section precision.

Actual when calculating, because wavelength X _OffThe same λ of absorption cross section _OnCompare and to ignore, often only pay close attention to λ _OnRelated parameter values.Select λ _OnAs λ, broadening coefficient b _L(air, λ), b _L(CO ₂, λ) and temperature correlation index n _a(λ),

Adopt corresponding value, adopt formula (3) to calculate, the result namely can be used as the required Lorentz full width at half maximum of this step.

Embodiment is with reference to nature CO ₂The vertical distribution of concentration is with CO ₂Gas is preset as 0.04% with the initial value of the volume ratio χ of air.

Step 2 judges whether to satisfy the iteration termination condition, is process ends then, otherwise enters step 3.

The iteration termination condition can adopt default iterations in the step 2.Generally can be made as 3 times or 4 times.During flow scheme design, can be in first time during execution in step 1, the initial value that makes the current iteration number of times is 1, current iteration number of times=current iteration number of times+1 when carrying out step 3.

Step 3 obtains CO by following formula conversion ₂The concentration of gas and volume ratio χ

$\left(4\right),C=\frac{{6.02\×10}^{20}}{22.4}\×\mathrm{\χ}\×\frac{T_0}{T}\×\frac{P}{P_0}$

In the formula, C is CO in every cc of air ₂The molecule number;

Then return step 1, according to the new CO that calculates ₂The concentration of gas and volume ratio χ recomputate the Lorentz full width at half maximum.

The present invention relates to CO in the differing heights atmosphere ₂The impact of temperature, pressure is considered in the conversion of molecular conecentration and volume ratio χ simultaneously.

Lorentz full width at half maximum FWHM directly has influence on DIAL and finds the solution CO ₂The key component of concentration---absorption cross section.According to step 1 gained Lorentz full width at half maximum, obtain CO by the DIAL equation ₂CONCENTRATION DISTRIBUTION, DIAL equation are formula (1).This result directly shows with molecular conecentration C.

Formula (3) is tested under laboratory condition and is verified, is the CO that pours the fixed volume ratio in container ₂, what obtain is that definite value is theoretical; At laser radar field, CO ₂Concentration with the height significant change, this is the value problem.To this, take this definite value theory as the basis, the present invention proposes two kinds and solve thinking: the one, direct band value is found the solution FWHM, and the 2nd, adopt the method for iteration to find the solution.

Specifically, the first thinking thinks that namely χ is 0.04% (with reference to nature CO ₂The vertical distribution of concentration) and the volume ratio true value when calculating FWHM, directly bring formula into and calculate, can obtain rapidly result of calculation, little on the impact of precision simultaneously.Its advantage is, can show fast, in real time CO when carrying out observation experiment ₂The vertical distribution situation of concentration is convenient to directly check CO ₂Concentration results can not repeat improper value to introduce and calculate simultaneously, has very high reference value for laser radar system debugging work.In the step 1 according to CO ₂Gas adopts the Lorentz full width at half maximum of formula (3) calculating namely as result of the present invention with the default initial value of the volume ratio χ of air, need not to carry out subsequent step again.During implementation, can realize by default iterations is made as 1.

The second thinking is to adopt the mode of iteration, sets CO ₂Volume ratio initial value 0.04% can be finally inversed by CO as iteration variable through an iteration ₂CONCENTRATION DISTRIBUTION, this result directly shows with molecular conecentration, be converted into χ by formula (4), at this moment, χ be one with highly relevant profile, corresponding with temperature, pressure values, observing formula (3) can find, FWHM is synthermal, pressure, χ are closely related, and three amounts all are functions of height, the χ profile can be applied directly in the iteration second time, can satisfy precision through 3 ~ 4 iteration.Inversion result precision after the iteration obviously is better than the first thinking, but higher for the data handling system performance requirement, and calculating time delay is larger.

At the experiment initial stage, the laser radar echo signal is unsatisfactory, and often occur that volume ratio substantially exceeds or less than the situation of normal atmosphere level, adopt the first scheme, the correctness that can check fast, in real time the result, the system of being convenient to regulates; In the experiment later stage, behind the system stability, under the prerequisite that various hardware, software issue have overcome, the possibility that the error secondary is quoted reduces greatly, must use the method for iteration for the accurate processing of data, improves precision.

Specific embodiment described herein only is to the explanation for example of the present invention's spirit.Those skilled in the art can make various modifications or replenish or adopt similar mode to substitute described specific embodiment, but can't depart from spirit of the present invention or surmount the defined scope of appended claims.

Claims (4)

1. Difference Absorption Atmospheric CO ₂Laser radar atmospheric pressure broadening modification method is characterized in that, may further comprise the steps:

Step 1 adopts following formula to calculate the Lorentz full width at half maximum,

${\mathrm{\γ}}_L(P,T,\mathrm{\λ})=P\×\{b_L(\mathrm{air},\mathrm{\λ})\×(1-\mathrm{\χ})\×{\left[\frac{T_0}{T}\right]}^{n_a\left(\mathrm{\λ}\right)}+b_L({\mathrm{CO}}_2,\mathrm{\λ})\×\mathrm{\χ}\×{\left[\frac{T_0}{T}\right]}^{n_{C{O}_2}\left(\mathrm{\λ}\right)}\}---\left(3\right)$

In the formula, γ _L(P, T, λ) represents the Lorentz full width at half maximum, and P is pressure data, and λ is wavelength, and T is temperature data, T ₀Standard temperature, b _L(air, λ) is the atmospheric pressure broadening coefficient of Accurate Measurement, b _L(CO ₂, λ) be CO ₂Gas from the broadening coefficient, χ is CO ₂Gas is with the volume ratio of air, n _a(λ),

Value is respectively atmosphere and CO ₂The gas temperature index of correlation;

Step 2 judges whether to satisfy the iteration termination condition, is process ends then, otherwise enters step 3;

Step 3 according to step 1 gained Lorentz full width at half maximum, obtains CO by the DIAL equation ₂CONCENTRATION DISTRIBUTION, this result directly show with molecular conecentration C, transform by following formula and obtain CO ₂The concentration of gas and volume ratio χ

$C=\frac{{6.02\×10}^{20}}{22.4}\×\mathrm{\χ}\×\frac{T_0}{T}\×\frac{P}{P_0}---\left(4\right)$

In the formula, C is CO in every cc of air ₂The molecule number;

Return step 1, according to the new CO that calculates ₂The concentration of gas and volume ratio χ recomputate the Lorentz full width at half maximum.

2. described Difference Absorption Atmospheric CO according to claim 1 ₂Laser radar atmospheric pressure broadening modification method is characterized in that: the iteration termination condition adopts default iterations in the step 2.

3. described Difference Absorption Atmospheric CO according to claim 2 ₂Laser radar atmospheric pressure broadening modification method is characterized in that: in the step 1, according to CO ₂Gas adopts formula (3) to calculate the Lorentz full width at half maximum with the default initial value of the volume ratio χ of air, and default iterations is made as 1.

4. according to claim 1 and 2 or 3 described Difference Absorption Atmospheric CO ₂Laser radar atmospheric pressure broadening modification method is characterized in that: in the step 1, and CO ₂Gas is 0.04% with the default initial value of the volume ratio χ of air.