CN102519892A - Spectral line drift participated regression algorithm method for correcting spectral line drift in differential optical absorption spectral measurement - Google Patents
Spectral line drift participated regression algorithm method for correcting spectral line drift in differential optical absorption spectral measurement Download PDFInfo
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- CN102519892A CN102519892A CN2011104051583A CN201110405158A CN102519892A CN 102519892 A CN102519892 A CN 102519892A CN 2011104051583 A CN2011104051583 A CN 2011104051583A CN 201110405158 A CN201110405158 A CN 201110405158A CN 102519892 A CN102519892 A CN 102519892A
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- 230000003595 spectral effect Effects 0.000 title claims abstract description 44
- 238000010521 absorption reaction Methods 0.000 title claims abstract description 32
- 238000000034 method Methods 0.000 title claims abstract description 22
- 230000003287 optical effect Effects 0.000 title claims abstract description 9
- 238000005259 measurement Methods 0.000 title abstract description 14
- 238000001228 spectrum Methods 0.000 claims abstract description 41
- 238000000862 absorption spectrum Methods 0.000 claims abstract description 21
- 239000003344 environmental pollutant Substances 0.000 claims abstract description 17
- 231100000719 pollutant Toxicity 0.000 claims abstract description 17
- 238000004364 calculation method Methods 0.000 claims abstract description 13
- 238000012937 correction Methods 0.000 claims abstract description 11
- 238000012417 linear regression Methods 0.000 claims abstract description 5
- 238000013016 damping Methods 0.000 claims description 3
- 239000011159 matrix material Substances 0.000 claims description 3
- 238000001658 differential optical absorption spectrophotometry Methods 0.000 abstract description 26
- 239000007789 gas Substances 0.000 description 21
- 238000005516 engineering process Methods 0.000 description 6
- 238000011160 research Methods 0.000 description 5
- RAHZWNYVWXNFOC-UHFFFAOYSA-N Sulphur dioxide Chemical compound O=S=O RAHZWNYVWXNFOC-UHFFFAOYSA-N 0.000 description 4
- 238000002715 modification method Methods 0.000 description 3
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000003556 assay Methods 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 239000003546 flue gas Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000012544 monitoring process Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 238000013519 translation Methods 0.000 description 2
- 239000005436 troposphere Substances 0.000 description 2
- 229910052724 xenon Inorganic materials 0.000 description 2
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 2
- YZCKVEUIGOORGS-OUBTZVSYSA-N Deuterium Chemical compound [2H] YZCKVEUIGOORGS-OUBTZVSYSA-N 0.000 description 1
- 241000139306 Platt Species 0.000 description 1
- 244000141353 Prunus domestica Species 0.000 description 1
- 238000012952 Resampling Methods 0.000 description 1
- 238000003915 air pollution Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 229910052805 deuterium Inorganic materials 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000000295 emission spectrum Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 239000005437 stratosphere Substances 0.000 description 1
- 230000009897 systematic effect Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
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Abstract
The invention relates to a determination method for gas components and especially to a method for spectral line drift correction in differential optical absorption spectral measurement when differential optical absorption spectroscopy (DOAS) is employed to measure gas components. According to the invention, drift of signal spectrums is considered as an inherent absorption structure of a system, during calculation of the content of pollutants through least square multivariate linear regression, the structure participates as an absorption cross section of the pollutants in the calculation, and therefore, absorption signal distortion influence caused by a specific lamp spectrum at fixed offset can be deducted, thereby obtaining correct concentration content of the pollutants. After treatment by using the method, influence of the spectral line drift on an absorption spectrum is substantially reduced, and influence of the spectral line drift on fitting results of DOAS calculation is basically eliminated.
Description
Technical field
The present invention relates to a kind of assay method of gas composition, relate in particular to and adopt the spectral drift modification method in the difference absorption spectrum measurement in the DOAS measurement gas component.
Background technology
The eighties in 20th century, Platt etc. are applied to difference absorption spectrum technology (DOAS) in the atmospheric research of troposphere.From then on, the DOAS technology has obtained fast development, and many research institutions are according to the research characteristics of oneself, Application of DO AS technical design instrument.These application comprise air pollution monitoring, volcanic gas analyse atmos troposphere, stratosphere gas composition monitoring etc.
To the end of the eighties; The DOAS technology is extensively approved as the gas detection means; OPSIS company has confirmed the basic structure of DOAS system, and other companies also release the commercial DOAS system of oneself one after another, and on structure, hardware, software algorithm, have proposed a lot of improvement thinkings.Nineteen ninety, Axelson etc. have at first adopted Cassegrain telescope designs simplification device.1992, John M.C etc. adopted photodiode array (PDA) to replace photomultiplier (PMT), gather spectroscopic data fast, and had realized the robotization of measuring.Nineteen ninety-five, Theo Brauers etc. has improved between the pixel that the PDA detector brings difference to the influence of measurement result.1996; Stutz etc. improve the retrieving concentration method, in order to eliminate spectral shift, stretching and the compression influence to measuring, adopt least square and nonlinear Levenberg-Marquardt method; The algorithm that replaces the pure linearity of forefathers has improved the accuracy of measurement result.2000, Ahilleas etc. proposed the retrieving concentration method to high meticulous spectrum.Different structure, different detectors, the proposition of algorithms of different and application have promoted the development of DOAS technology.
At present, the DOAS systematic research mainly concentrates on Sweden (the OPSIS_DOAS system of OPSIS AB company), Germany (the HMT DOAS system of Heidelberg university and the exploitation of Hoffmann company), the U.S. (the DOAS2000 system of thermal environment research institute), France (the DOAS system of Environment SA exploitation) and Russia states such as (the DOAS 4R of Eridan-1 Science & Technology Center exploitation).
The DOAS technology just is being based on gas with various has differing absorption spectrum to light, is called gas " fingerprint " absorption characteristic to light, distinguishes different materials, measures their concentration.
The spectrometer that in DOAS flue gas detector, adopts is that light beam is passed through slit, through grating beam splitting, finally is incident upon the required spectrum of acquisition on the PDA detector.Theoretical analysis and experimental result show, position and the incident direction and the depth of parallelism of light beam that spectrophotometric spectra is incident upon on the PDA have much relations.For relative position constant light path and spectrometer, because all devices are all fixed, we can come the wavelength coordinate of correct nominal light spectrometer through spectral calibration.But for the on-fixed light path, such as for the spectral line with many light beams of same set of spectrometer measurement, one group of wavelength scaling parameter just not necessarily satisfies the spectral calibration under the various light path situation.Because can't obtain the incident beam of absolute parallel.Fig. 1 illustrates the production process of this phenomenon.
For the spectrum that changes more slowly; This phenomenon is also not obvious; Because the difference of the signal of the vicinity that faint line drift causes
with
is also little; The error of calculation of the Difference Absorption spectral line that is produced is also less relatively; Generally can ignore. such as our employed deuterium lamp; Its signal spectrum is quite mild; We have measured two original lamp spectrums
and
through different light paths, respectively corresponding two corner reflectors.Where
is measured using an internal reflector lamp spectrum,
is no absorption gas sample cell with a sample pool-side corner reflectors measured.In theory if two identical words of optical device material of measuring light path; Absorption characteristic should be consistent; So
/
also should be a horizontal line, it highly is the ratio of the transmitance of two light paths.Actual ratio spectral line
often has certain fluctuation such as Fig. 2.Because what relation the influence of the relativity shift of spectral line to measuring does not have with concrete wavelength value, horizontal ordinate is the port number of actual PDA detector in therefore scheming, and is not true wavelength value.From figure, can see that absorption line is straight line basically when modulating signal is stronger, the influence of the faint skew of spectral line shows especially out when signal is more weak, causes absorption line that bigger disturbance is arranged.
And when we adopt the light source of emission spectrum structure big rise and fall (flash of light xenon lamp); Identical analytic process can be seen; For the bigger light source of changes in amplitude, line drift causes influences highly significant, to such an extent as to the structure of its generation is very important with respect to real pollutant; If do not add processing, make the multiple linear built-up pattern of dusty gas can not correctly describe the DOAS absorption spectrum.Thereby pollute the gas concentration value regression results and have very big error with actual concentration value.The structure that produces when spectral line shift even similar the time, can produce full of prunes result with certain gas standard absorption cross section.
Chinese invention patent application (application number: 2011103727620; The applying date: 2011-11-22) disclose based on the gas component concentrations inverting of difference absorption spectrum and calculate assay method; The prerequisite that this method utilizes least square to fit inverting concentration in actual measurement is to obtain the Difference Absorption cross section that all absorb gas; But the gas absorption cross section is often with temperature, and the pressure change influence is very greatly also quite complicated.Gas with various all has characteristics separately, causes the Compression and Expansion of spectrum also different, revises quite loaded down with trivial details.In addition, the drift that the actual absorption spectrum that records tends to produce spectral line owing to reasons such as light path alignings, this error of bringing to inversion algorithm is fatal.
In DOAS measures, measured lamp spectrum and signal spectrum are required its horizontal ordinate, just the wavelength coordinate is wanted strict registration.Otherwise small skew may bring very big interference when calculating.If avoid the generation of this spectral line shift in the time of can't be from waveform acquisition, just need from the late time data processing, handle, to eliminate this influence.
In the ideal case, the degree of correlation of lamp spectrum that is obtained and the signal spectrum of not passing through any absorbing medium is very high, and being the maximal correlation △ t constantly that obtains behind association's related operation should be 0:
And if have faint skew owing to light path reason and KPT Scatter reason cause original lamp spectrum and do not have the absorption signal spectrum, then the △ t that obtains of related operation is with non-vanishing, its value is relative side-play amount between signal spectrum and the lamp spectrum.The most directly solution can be done reference with the lamp spectrum here, and the side-play amount of composing with respect to lamp with signal spectrum is done correction to signal spectrum as system's inherent variability in computing, then can eliminate the influence of line drift to the difference absorption spectrum computing.
Summary of the invention
In order to solve the spectral drift in the above-mentioned difference absorption spectrum measurement; The purpose of this invention is to provide the spectral drift modification method in other a kind of difference absorption spectrum measurement; After adopting this method to handle; Spectral line shift significantly reduces the influence of absorption spectra, and the influence of the fitting result that final DOAS is calculated is also eliminated basically.
In order to realize above-mentioned purpose, the technical scheme below the present invention has adopted:
The absorbing structure that this method is brought spectral line shift is participated in polynary least-squares linear regression and is calculated as a kind of absorption cross section of pollutant:
Wherein
is the standard absorption cross section of pollutant to be measured,
be the absorbing structure that spectral line shift produced;
is the measured signal spectrum; Separate this matrix; Then resulting
is the damping capacity of whole optical system;
is the unit volume molecular number of pollutant to be measured,
then represented the influence that spectral line shift produced big or small.
The present invention is owing to adopted above-mentioned technical scheme; With the skew of signal spectrum intrinsic absorbing structure as system; Then when doing least square multiple linear regression calculating pollutant load; This structure is participated in calculating as the absorption cross section of " pollutant ", the absorption signal distortion effects deduction that then can specific lamp spectrum be caused on fixing side-play amount equally, thus obtain correct pollutant levels content.After adopting this method to handle, spectral line shift significantly reduces the influence of absorption spectra, and the influence of the fitting result that final DOAS is calculated is also eliminated basically.
Description of drawings
Fig. 1 is the spectral drift phenomenon figure in the difference absorption spectrum measurement.
Fig. 2 is the actual ratio spectrum.
The original lamp that Fig. 3 is obtained for 1 couple of embodiment is composed and is not had absorption signal and compose the spectrum that carries out related calculation and obtain.
The signal spectrogram that the nothing that Fig. 4 calculates for embodiment 1 corrected spectrum absorbs.
The optical absorption density that the nothing that Fig. 5 calculates for embodiment 1 corrected spectrum absorbs.
Embodiment
Embodiment 1 spectral line translation revised law
For the purpose of the typical case, the high pressure flash of light xenon lamp that employing original signal intensity of variation is bigger is done light source, the original lamp that is obtained is composed and do not had the absorption signal spectrum carry out related calculation, and the result is as shown in Figure 3:
The result shows that for this optical system, measured lamp spectrum and measuring-signal spectrum exist certain skew, related coefficient maximum to be lamp and the most identical part of signal, and through interpolation calculation, we obtain the wavelength shift amount of the relative lamp spectrum of signal spectrum.
For eliminating the influence of side-play amount, signal spectrum is made offset correction, because the spectral line shift amount possibly not be to measure the integral multiple of port number, so correction is inserted in needing to adopt to the Difference Absorption spectrum.Through interior slotting resampling, the signal spectrum after the faint skew that can obtain to revise, signal spectrum and optical absorption density that the nothing that calculates for corrected spectrum like Fig. 4, Fig. 5 absorbs.
Can find out that after treatment, spectral line shift significantly reduces the influence of absorption spectra.The influence of the fitting result that final DOAS is calculated is also eliminated basically.
For our experimental system and since the acquisition testing of each gas to be measured all the someone be the manual operation process, the spectral shift amount is mostly to be that artificial enchancement factor causes, and can't revise data through the spectral shift amount of prior mensuration.But specific to for flue SO
2Measurement owing to have only SO basically at the 280-320nm wave band
2A kind of absorption of flue gas; Behind the gas absorption spectra that at every turn collects this wave band; Can adopt the sulphuric dioxide absorption cross section and the gas absorption spectra that are pre-stored in the computing machine to make related operation; Be absorbed spectrum with respect to the side-play amount of absorption cross section, again absorption spectrum is made offset correction after utilization DOAS inversion algorithm calculate sulfur dioxide concentration.Repeatedly experiment is done data and is on average shown (like following table 5-1), can finely improve the accuracy of DOAS inversion algorithm with the method.
Because also can there be certain enchancement factor in the line drift amount of actual DOAS system, when doing flue sulphuric dioxide and absorb inverting, all utilize SO at every turn
2The method of absorption cross section correction absorption spectrum drift should obtain better inversion result.
The improvement of inverting concentration after the correction of table 1 process spectrum
| Actual absorption gas concentration (ppm) | 34.5 | 70.5 | 295 | 961 | 1970 |
| Revised inverting concentration (ppm) | 41.3 | 70.1 | 296.9 | 997.4 | 1884 |
| Unmodified inverting concentration (ppm) | 46.5 | 87 | 316.6 | 863.4 | 2138 |
Embodiment 2Line drift is participated in the regressing calculation method
If spectral line shift has repeatability, " absorbing structure " that then can spectral line shift be brought participated in polynary least-squares linear regression and calculated as the absorption cross section of a kind of " pollutant ":
Wherein
is the standard absorption cross section of pollutant to be measured,
be " absorbing structure " that spectral line shift produced.
is the measured signal spectrum; Separate this matrix; Then resulting
is the damping capacity of whole optical system;
is the unit volume molecular number of pollutant to be measured,
then represented the influence that spectral line shift produced big or small.
Adopt high concentration standard gas to configure the sulfur dioxide gas of 100ppm, 500ppm and three kinds of concentration of 1000ppm; With embodiment 3 described methods computing method are made to revise its content of back actual measurement with embodiment 2 respectively; The measured value of correction is made in contrast, obtains the comparing result like table.
When computing method are not done any correction, directly make inverting obtains after the DOAS computing pollutant load and actual value and differ bigger with measured spectral line.And two kinds of modification methods can reduce because the concentration error that the spectral line registration problems causes more significantly.Can find out that therefrom method of the present invention (line drift is participated in the regressing calculation method) slightly is better than the method (spectral line translation revised law) of embodiment 2.
Claims (1)
- Line drift participate in regressing calculation method correction difference absorption spectrum measure in the method for spectral drift, it is characterized in that absorbing structure that this method brings spectral line shift absorption cross section as a kind of pollutant, participate in polynary least-squares linear regression and calculate:X wherein 1(λ) be the standard absorption cross section of pollutant to be measured, x 2(λ) be the absorbing structure that spectral line shift produced; Y (λ) separates this matrix, then resulting u for the measured signal spectrum 0Be the damping capacity of whole optical system, u 1Be the unit volume molecular number of pollutant to be measured, and u 2Then represented the influence that spectral line shift produced size.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104198416A (en) * | 2014-09-15 | 2014-12-10 | 南京国电环保科技有限公司 | Real-time compensation method of measurement errors caused by spectrograph wavelength drift |
| CN104897599A (en) * | 2014-03-07 | 2015-09-09 | 香港城市大学 | Method and device for detecting substances |
| CN106680221A (en) * | 2016-12-14 | 2017-05-17 | 重庆川仪自动化股份有限公司 | Compensation method for wavelength shift based on xenon lamp spectrum |
-
2011
- 2011-12-08 CN CN2011104051583A patent/CN102519892A/en active Pending
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104897599A (en) * | 2014-03-07 | 2015-09-09 | 香港城市大学 | Method and device for detecting substances |
| CN104198416A (en) * | 2014-09-15 | 2014-12-10 | 南京国电环保科技有限公司 | Real-time compensation method of measurement errors caused by spectrograph wavelength drift |
| CN106680221A (en) * | 2016-12-14 | 2017-05-17 | 重庆川仪自动化股份有限公司 | Compensation method for wavelength shift based on xenon lamp spectrum |
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