A Study On Atmospheric Monitoring Based On Differential Optical Absorption Spectroscopy

Since applied in atmosphere monitoring at the end of 1970`s, differential optical absorption spectroscopy(DOAS)have made quiet great progress. With advantages of its lower equipment expenses and excellent monitoring capability, DOAS technique will own broad prospect at home.The article mainly includes the design of experimental set and concentration retrieve arithmetic. As DOAS technique is a kind of weak light detecting technology, it is the key to increase the SNR (Signal-to-Noise) of spectral signal. So the article introduces in details the design of the experimental set at the first work. The other work is to design the method of the retrieval of concentrations of the interest gases. Because of change of the temperature and atmosphere pressure, misalignment arises between the measured spectra and the reference. The misalignment will make the results of the retrieval wrong. So the analysis of calibration is an emphasis in the article.The article provides the demonstrations of the light source, transmitting/receiving set and homochromor. The whole work is to fix on the sets and select the parameters of them. At the end of the design of sets, a whole set is achieved by assembling the three main parts.As nonlinear parameters are introduced in process of the calibration of spectral misalignment, the linear and nonlinear least square methods are used in the retrieval procedure in the article. In the article, the mixed least squared method defined as MLSM method. Detailed analysis of the method and the errors brought by the method is performed. Three conclusions are attained among the numerical simulations: First, the LSM method is the optimum method to retrieve the concentrations of the gases. Second, the MLSM method does well in calibrating the misalignment. Third, only if the SNR is higher, the results of the retrieve can be attained truly, and the errors are in the permitted range; however when the SNR is very low, the reliability of the retrieve will decrease.The work at the design of the hardware of the DOAS set and the analysis of the method of the concentration retrieval can be seen as the important reference to the application of the DOAS. Through the work described in the article, much experience is accumulated for the research in the field.