Study Of Atmospheric Spectroscopy And Mie Scattering

With the development of our society, the environment is being polluted. Theindustry has got rapid progress, leading to the more and more serious atmospherepollution, including the gas pollution (e.g. sulfur dioxide, nitrogen dioxide etc) andaerosol pollution etc. The gas such as sulfur dioxide and nitrogen dioxide is the mainreason of acid rain, and also is the threat against peoples. And the aerosol, to someextent, is indispensable to human, for it is the requirement for raining, but theaerosol will also do harm to human's health if it is too much. Therefore, suchpollutant is necessarily to be monitored effectively. In the diversified monitoringmethod, the optical technique is of excellence because of its high sensitivity, andhigh speed, what is more, it will not produce new pollutant. This technique is thesubject of this thesis.Firstly showed in this thesis is the research of monitoring nitrogen dioxide usingdifferential optical absorption spectroscopy(DOAS) method. DOAS is based on theBeer-Lambert law, the absorption information could be got by comparing the samplespectroscopy and the reference spectroscopy. Of which the key problem isseparating the absorption structure of nitrogen dioxide (rapid-variation absorptionstructure) and the summation of other extinction structures (slow-variationabsorption structure). In the traditional retrieve of NO₂ density, the choice ofslow-variation fitted curves is of random, which, it is discovered by this thesis, maylead to great error of the result. To solve the problem, this thesis advanced a methodsearching for the slow-variation absorption structure through nonlinear regression,by which the precision of retrieved NO₂ density is improved obviously. The methodof monitoring the NO₂ density by scattering light is also displayed, the advantage ofwhich is the high signal-to-noise, needlessness of accurate tacking of the sun. Andby this method the NO₂ density of ChengDu was got. And by the Rayleigh scattering,a primary model to retrieve the vertical distribution profile (VDP) of NO₂ isestablished, by this model the VDP of NO₂ of ChengDu is retrieved, to some extent,the retrieved result can reflect the real VDP Of NO₂, but after all, the modal is quite simple and rough, to get the VDP of NO₂ accurately, the information of atmospheretransmission and the photochemistry is indispensable.The following research is about the measurement of the aerosol size-distributionand density, which is based on the Mie Scattering theory combine to themeasurement of the aerosol's optical depth. In past, the retrieval is founded on thedependence-pattem, that is to suppose the size-distribution to be some type offunction (Junge or Gamme etc) prior, and then calculate the parameters of thefunction through the measured optical depth to obtain the concrete size-distribution.In addition, because of the complexity of the Mie theory, in past the rigorouscalculation is always replaced by approximate arithmetic. All of above will lead toerror of the results, this paper researched the independence-pattern retrieving method,which used the rigorous Mie Scattering theory. The kemel problem of theindependence-pattem is to calculate a matrix, but the matrix is of high morbidity,which will lead to the instability of the result. In order to get the stable retrievalresult, the common linear-regress, Simulated Annealing Arithmetic (SAA) and theGenetic Arithmetic (GA) is used in the retrieving simulation respectively, throughthe simulating it is found that the GA is the best arithmetic. Based on which theaerosol size-distribution and density of ChengDu was got. In addition, the paperdisplayed the detailed analysis of error, that is the influence of scattering light on theresults, which showed little influence in usual atmosphere condition.Finally is the calculation of the scattering chroma of spheric particle at differentscattering angle based on the Mie theory and chroma theory, a high resolutionchroma chart is displayed. Based on which the Glory phenomenon is simulated, therelation of Glory and the fogdrops size is discussed in detail, it is found that thecolor of Glory is determined by size distribution of surface fogdrops, none but thecontent of large surface fogdrops achieve some level, it is possible to observingGlory. And the sky chroma is also simulated. The multi-scattering is replaced by asimple model in the simulation.The above research result is significative to monitoring the atmosphere pollutionusing optical method and the research of the atmosphere optical phenomenon.