The Experimental Study Of Satellite Retrieving Dust Aerosol Optical Thickness Over Land

Dust aerosols are an important factor influencing the earth's climate and environment.They affect the radiation budget of the earth-atmospheric system and are intricately linked to atmospheric circulation,the cloud processes,hydrologic cycle, short-term weather change and long-term climate forecast.In this dissertation,Aerosol Robotic Network(AERONET) SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University) Version 2 Level 2 dataset,whose quality is assured after having gone through a rigorous calibration and cloud screening process,and Terra Moderate-resolution Imaging Spectroradiometer(MODIS) Level 1B multi-spectral data with 1 km spatial resolution are employed.Based on Look Up Table,calculated using the 6S atmospheric radiation transportation model,we perform the retrieval study of dust aerosol optical thickness over semi-arid region of Loess plateau,the main dust region of China.The main contents are summarized as follows:1) Using the aerosol remote sensing dataset from AERONET for the period of Sep 2006 to Aug 2007 at SACOL site,atmospheric aerosol optical characteristics were analyzed.The results show not only that aerosol optical thickness,(?)ngstr(o|¨)m exponent,volume size distribution,refractive index and single scattering albedo vary season by season,but also that dust can impact aerosol optical characteristics especially in spring.2) The aerosol model was built using SACOL data,and then the atmospheric correction of MODIS/Terra was performed by the 6S atmospheric radiation transport model.The results show that the relationship of 0.47vs0.66μm surface reflectance may be stronger than 0.47vs2.12 surface reflectance because it has a higher correlation and is more stable.The VISvs2.12 surface reflectance relationships do not show dependence on scattering angle.Therefore,the final VISvs2.12 surface reflectance relationships are simple ratios,and are different from the surface reflectance ratios used in the atmospheric correction of the continental model in the 6S.3) According to the sensitivity study of surface reflectance against apparent reflectance at different channels and the range of surface reflectance over SACOL,we chose the 0.66μm channel as retrieval channel.The four schemes of surface reflectance based on the data of atmospheric correction were developed and then the retrieval of dust aerosol optical thickness over 10×10km~2 centered in the SACOL site was performed.The results show that the distribution of dust aerosol optical thickness can reasonably describe region characteristics,so the operational algorithm is valid. The best retrieval result was derived from the atmospheric correction scheme used in the aerosol model built by SACOL data with consideration for the(?)ngstr(o|¨)m exponent. The relative error is -7.3%.We performed quantitative analysis of error by designing a numerical test;the results show that the retrieval is stable.