The Inversion Study Of Aerosol Optical Depth Based On The MODIS And HJ-1A/B In Greater Xi’an Area

Global environmental problems, especially the city air pollution, have been increasingly affected human’s life, development and their life quality. As an important parameter to reflect the dirty degree of particulate matter in the atmospheric environment, optical and physical properties of Aerosol Optical Depth (AOD) have got attention of experts and received their long-term research. AOD retrieved from satellite remote sensing data has such advantages as fast speed, wide range and low cost. It can not only monitor the temporal and spatial distribution of the surface of aerosols, but also provide more reliable technical measures for such aerosols’ laws as aggregation, migration and dissipation. Based on the principles of remote sensing aerosol and through the widely used Dark Dense Vegetation method at present, the thesis used Terra/MODIS L1B data and HJ-1A/B data, made a lookup table by 6S model, and quantitatively disclosed the distribution pattern of AOD in Greater Xi’an area. Then adopting fractal dimension method, the thesis focuses on features such as aggregation, migration, dissipation of the aerosols in 2013 and finally achieved the fractal dimension image of AOD with the visualization method. This research mainly obtained the following conclusions:1) According to the linear relationship between surface reflectance near to the near-infrared band and visible light band respectively, the author calculated the inversion images of AOD, compared them with NASA aerosol products and finally realize the calculation of the correlation coefficients of two kinds of image data by using ArcGIS band set statistics. The result showed that aerosol products provided by MODIS AOD and NASA showed relatively high correlation and consistency.2) The application of domestic environmental satellite data in the inversion of AOD in Greater Xi’an area. Based on the basic aerosol principle and adopting the NDVI threshold method to judge the dark pixels, the thesis made an inversion of the AOD of the study area, conducted a precision test as to the inversion results and associated them with the NASA aerosol products and the coefficient was 0.548 which indicated a good correlation. This conclusion proved that the application value and potential of domestic high resolution remote sensing satellites in remote sensing inversion.3) The application of fractal dimension in the inversion result analysis of AOD in remote sensing. Time series analysis was used to analyze the basic rule of aerosol’s gathering-dissipation in three of time periods in Xi’an, and the triangular prism algorithm of fractal dimension was applied to analyze and evaluate remote sensing aerosol images. Fractal dimension applied in aerosols remote sensing inversion successfully by means of visualization. Aerosol aggregation-dissipation features are as follows:(i) Owing to the basic geographical terrain characteristics of Xi’an basin, clustered aerosol outbreaks are mainly from atmospheric particles delivered by the west, northwest, north winds. Similarly, the dissipation is also caused by atmospheric motion to leeward area, i.e. the North China Plain. These processes last short time and show strong dynamics, (ii) In the conditions of static wind and local atmospheric control, aerosol occurred mainly from the particulate emission of urban area and the underlying surfaces, etc. The process presented such diffusion characteristics as from the center to the edge without large migration and dissipation. (iii) Aerosol aggregation after the atmospheric motion crossing the area mainly presents such features as large scale, all coverage, even distribution in the terrain basin and the dissipation follows by air humidity as well as particles sedimentation. For instance, continuous aggregation leads to severe hazy weather, and aerosol retrieval value will also appear high values in large areas.In the process of studying aerosol controlled by satellite remote sensing, it was difficult to realize continuous dynamic monitoring because of the shortcomings of unitary satellite materials such as unsatisfactory image quality and data missing. In the future we can adopt multi-source satellite sensor data and make full use of favorable conditions of Data Age, to construct a connection network applied in the surface site monitoring and multi-source satellite monitoring to measure AOD dynamic process, which has an important application value.