CN102879772B - 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 atmosphere CO 2 laser radar atmospheric pressure broadening modification method

Technical field

The present invention relates to 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 greenhouse gases principal ingredient, global climate is had to 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 region CO ₂source remittance multidate information, tackles growing carbon emission stress problems.DIAL is being surveyed CO ₂aspect 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 the absorption of atmospheric substance to laser beam energy.In order to get rid of the impact of other factors, the wavelength that employing two bundle difference are very little conventionally in DIAL is as 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 beam of laser is absorbing paddy place, and dampen out possibility that it is subject to is little, is called λ _off.By measuring the Atmospheric CO increasing with highly ₂the variation absorbing carrys out 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 is positioned at the height R that atmospheric envelope is higher ₂the height R lower with atmospheric envelope ₁between intermediate altitude), the CO that DIAL is surveyed ₂concentration equation can show as following form:

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

In formula, Ng represents CO 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 place obtains, Ps (λ _on, R ₁) expression employing wavelength X _onsurvey height R ₁the echoed signal intensity that place obtains, Ps (λ _on, R ₂) expression employing wavelength X _onsurvey height R ₂the echoed signal intensity that place obtains, Ps (λ _off, R ₁) expression employing wavelength X _offsurvey height R ₁the echoed signal intensity that place obtains.From above formula, the density that is detected component is relevant with the difference of the ratio of two passage echoed signals and the absorption cross section at two wavelength places.σ _g(λ) value is relevant to 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 Lorentz profile.Along with the increase of height, the fluctuation that the synthermal existence of pressure is larger, causes Lorentz profile to change to some extent, must revise it, i.e. atmospheric pressure broadening correction, to obtaining higher precision.

The classical way that adopted in the world is at present the relevant theory of atmosphere radiation, solves FWHM, solves pressure broadening problem, has following computing method:

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

γ in formula _l(P, T) represents 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 ₀(273K) halfwidth time, n is temperature correlation index.

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

The art not yet has relevant solution to occur.

Summary of the invention

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

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, comprises the following steps: step 1, and adopt following formula to calculate 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 formula, γ _l(P, T, λ) represents 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 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 meet iteration termination condition, is process ends, otherwise enters step 3;

Step 3, according to step 1 gained Lorentz full width at half maximum, obtains CO by DIAL equation ₂cONCENTRATION DISTRIBUTION, this result directly shows with molecular conecentration C, by following formula, is transformed and is obtained 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 formula, C is CO in every cc of air ₂molecule number;

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

And iteration termination condition adopts default iterations in step 2.

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

And, in 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, according to choose (the present invention adopts 1.57 mum wavelengths) of experiment wavelength, adopted corresponding halfwidth γ ₀with temperature correlation index n, science, rationally more, inversion result is more accurate.Can solve the same problem that other wavelength (spectral line) data face simultaneously.The present invention has the following advantages and good effect:

1) forgone and classical be corrected in the uncertainty in value, avoided bringing into of new error;

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

3), according to actual scene demand, adopt respectively band value to solve with the method for iteration and there is dirigibility.Band value derivation speed is fast, can realize the real-time demonstration of experiment inversion result; The method of iteration can increase substantially inversion accuracy.

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

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 operation automatically, comprise the following steps:

Step 1, adopts following formula to calculate 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 formula, γ _l(P, T, λ) represents 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 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, first clear and definite employing formula (3) carries out the calculating of Lorentz full width at half maximum.This formula need to, with 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 formula _l(air), b _l(CO ₂) and temperature correlation index n _a,

with laser emission wavelength, λ is closely related, 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 _off.According to λ _onor λ _offfor parameter, formula (3) calculates accordingly, can obtain λ _onor λ _offabsorption cross section precision.

Actual when calculating, due to wavelength X _offthe same λ of absorption cross section _oncompare and can 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, result 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, by CO ₂gas is preset as 0.04% with the initial value of the volume ratio χ of air.

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

In step 2, iteration termination condition can adopt default iterations.Generally can be made as 3 times or 4 times.During flow scheme design, can perform step at 1 o'clock for the first time, the initial value that makes current iteration number of times is 1, current iteration number of times=current iteration number of times+1 while carrying out step 3.

Step 3, is transformed and is obtained CO by following formula 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 formula, C is CO in every cc of air ₂molecule number;

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

The present invention relates to CO in 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 solves CO ₂the key component of concentration---absorption cross section.According to step 1 gained Lorentz full width at half maximum, by DIAL equation, obtain CO ₂cONCENTRATION DISTRIBUTION, DIAL equation is formula (1).This result directly shows with molecular conecentration C.

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

Specifically, the first thinking thinks that χ is 0.04% (with reference to nature CO ₂the vertical distribution of concentration) the volume ratio true value and when calculating FWHM, directly brings formula into and calculates, and can obtain rapidly result of calculation, simultaneously little on the impact of precision.Its advantage is, while carrying out observation experiment, can show fast, in real time CO ₂the vertical distribution situation of concentration, is convenient to directly check CO ₂concentration results, can not repeat improper value to introduce and calculate simultaneously, for laser radar system debugging work, has very high reference value.In step 1 according to CO ₂gas, with the default initial value of the volume ratio χ of air, adopts the Lorentz full width at half maximum of formula (3) calculating as result of the present invention, without carrying out subsequent step again.During concrete enforcement, can be by default iterations be made as to 1 realization.

The second thinking is the mode that adopts iteration, sets CO ₂volume ratio initial value 0.04%, as iteration variable, can be finally inversed by CO through an iteration ₂cONCENTRATION DISTRIBUTION, this result directly shows with molecular conecentration, by formula (4), be converted into χ, now, 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 are all functions of height, χ profile can be applied directly to for the second time in iteration, through 3 ~ 4 iteration, can meet precision.Inversion result precision after iteration is obviously better than the first thinking, but higher for data handling system performance requirement, and calculating time delay is larger.

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

Specific embodiment described herein is only to the explanation for example of the present invention's spirit.Those skilled in the art can make various modifications or supplement 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. a Difference Absorption Atmospheric CO ₂laser radar atmospheric pressure broadening modification method, is characterized in that, comprises the following steps:

Step 1, according to CO ₂gas, with the default initial value of the volume ratio χ of air, adopts following formula to calculate Lorentz full width at half maximum,

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

In formula, γ _l(P, T, λ) represents 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 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 meet iteration termination condition, is process ends, otherwise enters step 3;

Step 3, according to step 1 gained Lorentz full width at half maximum, obtains CO by DIAL equation ₂cONCENTRATION DISTRIBUTION, this result directly shows with molecular conecentration C, by following formula, is transformed and is obtained CO ₂gas is with the volume ratio χ of air

$C=\frac{6.02\×{10}^{20}}{22.4}\×\mathrm{\χ}\×\frac{T_0}{T}\×\frac{P}{P_0}---\left(2\right)$

In formula, C is CO in every cc of air ₂molecule number, P ₀for standard pressure;

Return to step 1, according to the new CO calculating ₂gas recalculates Lorentz full width at half maximum with the volume ratio χ of air.

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

3. Difference Absorption Atmospheric CO according to claim 2 ₂laser radar atmospheric pressure broadening modification method, is characterized in that: in step 1, select the wavelength X of 1572.018nm _onas wavelength X, adopt formula (1) to calculate Lorentz full width at half maximum.

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