Study On A Two-dimensional Spatial Heterodyne Spectrometer For Atmospheric Nitrogen Dioxide Observations

Trace gases are micro constituents in the atmosphere,less than one part per million.But because of its high activity,it plays a vital role in the chemical reactions among the components in the atmosphere.Nitrogen dioxide,as a continuous broadband absorption trace gas,plays a major role in tropospheric and stratospheric chemistry and biogeochemical cycles.Therefore,it is of great significance to detect the nitrogen dioxide content in the atmosphere.The spatial heterodyne spectrometer has the advantages of small volume,no moving parts,high light flux,high spectral resolution and low requirements on a single component.So far,it has been successfully applied to spaceborne space medium radiation detection,atmospheric OH radical detection,atmospheric wind field detection and Raman spectrum detection.In this thesis,a monolithic two-dimensional spatial heterodyne spectrometer system for ground-based observation is built,and it is applied to the detection of atmospheric nitrogen dioxide for the first time.The system parameters are calibrated.By comparing the measured solar spectra with the simulation results,the correctness of the system recovered spectra is proved.The vertical column contents of nitrogen dioxide are retrieved by measured solar spectra and coincide closely with the simultaneously acquired OMI satellite data.Thus the ability of the system to detect nitrogen dioxide is proved.The main work of this thesis are summarized as follows:(1)Based on the theory of spatial heterodyne spectroscopy and the accurate installation and adjustment bonding technology independently developed by the laboratory,we independently design and fabricate a monolithic wide-spectral field-of-view expanded two-dimensional spatial heterodyne spectrometer with 455 nm as the central wavelength.The spectrometer is combined with other optical devices to design,adjust and package as a portable system.In order to ensure that the system can correctly recover the spectral range,complete calibration experiments are carried out for each parameter of the system.Different calibration methods are designed for measuring the system parameters,such as wavelength,efficiency curve,fringe visibility and instrument linear function.Mercury lamp,krypton lamp and xenon lamp are used to calibrate the positions and wavelengths of system.The normalized efficiency curve of the system is obtained by using a high voltage xenon lamp as white light source and a double-gratings monochromator.The maximum fringe visibility of the system and the instrumental line shape function are measured by using a single-wavelength narrow-linewidth laser and an integrating sphere as a monochromatic light source.(2)Two telescopes and an equatorial instrument are used to constitute the solar real-time tracking system,and the tracking system is coupled with the calibrated spatial heterodyne spectrometer system via an optical fiber to form the ground-based direct-sun observation system.In order to track the sun accurately in real time,the tracking system is adjusted.The direct solar spectra are acquired by the self-compiled interferogram acquisition software.(3)The method of obtaining measured spectral data by acquired interferogram is described in detail.During this process,the theory of phase distortion correction is discussed in principle.The phase distortion term of the corresponding band is calculated with the actual calibration data,and the two-dimensional phase distortion correction of this system is carried out.The result shows that the phase distortion correction can be negelected in the process of data processing.The measured solar spectra after processing is compared with the simulated theoretical solar spectra.The results agree well,which proves the correctness of the spectra obtained by the system.(4)The method of using the ground-based measured solar spectra to retrieve the total column contents of nitrogen dioxide in the atmosphere over Wuhan is studied.The calculation principle of differential optical absorption spectroscopy to obtain the vertical column contents of nitrogen dioxide are discussed in detail.Spectral correction and column contents inversion are carried out according to the measured spectra.The multi-day observation data are compared with the satellite observation data of OMI,which proves the reliability of system to retrieve atmospheric nitrogen dioxide contents.In this thesis,spatial heterodyne spectroscopy has been successfully applied to the detection of nitrogen dioxide in the atmosphere.It further broadens the application range of spatial heterodyne spectroscopy,and has guiding role for the ground-based remote sensing detection of other components in the atmosphere.