Retrieval Of Aerosol Optical Depth From POLDER/PARASOL Data Based On A Self-defined Aerosol Model

Atmospheric aerosols have a major impact on the global climate and environment.With the rapid development of economy in China,the emission of atmospheric pollutants has remained high,and the aerosol particles have become one of the main atmospheric pollutants.The retrieval accuracy and spatial distribution characteristics of Aerosol Optical Depth(AOD)which represents the degree of atmospheric pollution is a hot spot in atmospheric pollution fields.Now,the effective and large scale of atmospheric aerosol parameters obtained from the satellite remote sensing data can provide a scientific basis and technical support for regional aerosol monitoring and pollution prevention.Compared with the commonly used data such as MODIS,Polarization and Directionality of the Earth's Reflectance(POLDER)and Polarization and Anisotropy of Reflectance for Atmospheric Sciences coupled with Observation from a Lidar(PARASOL)data,can effectively distinguish the contribution of the atmosphere and surface,and reduce the influence of surface reflectance in the aerosol retrieval.The key to retrieve AOD using the polarization data is the choice of aerosol model.However,the complex aerosol composition and source,and the large difference between different regions,have resulted in no clear aerosol model.In this paper,a self-defined aerosol model was proposed to retrieve AOD from 2008 to 2009 in the Yangtze River Delta using POLDER/PARASOL data.The model was established using the volume percentages of four aerosol components(the dust,water-soluble,oceanic and soot particles)retrieved by Aerosol Robotic Network(AERONET)ground-based measurements.Furthermore,the retrieval results was compared with the AOD retrieved by the continental model under the same conditions,and the AERONET ground-based measurements were used as the verification data to verify the accuracy of AOD retrieved by different aerosol models.The main research conclusions of this paper are as follows:(1)The effects of different aerosol models on AOD retrieval and the characteristics of the four aerosol components(the dust,water-soluble,oceanic and soot particles)were analyzed Using second Simulation of the Satellite Signal in the Solar Spectrum(6S)radiative transfer model.The dust particles have strong scattering properties and absorption properties.The water particles have strong scattering effects and weak absorption as well as ocean particles,the soot particles only have the strong absorption.Furthermore,the different volume percentages of the four component particles generated the large error to the AOD retrieval results,and the results showed that the difference in the volume percentage of soot particles had the most effect.Therefore,it is very important to select the appropriate AOD model during the process of aerosol inversion.(2)The volume percentages of aerosol components in each season of the study area using AERONET ground-based measurements from 2008 to 2009 was estimated by the extinction method and the orthogonal test.The results show that obvious differences in the volume percentages of aerosol components in different seasons,but the water particles dominate.Furthermore,the concentration of dust particles was higher in spring and winter,while the concentration of soot particles was higher in summer and autumn,and the ocean particles were almost negligible.The annual average volume percentages of the four components in the study area were 0313,0.545,0.014 and 0.128 for dust,water-soluble,oceanic and soot particles,respectively,which were quite different from those of the continental model defined in the standard radiation atmosphere(SRA)aerosol models.(3)Two look-up tables were established using the self-defined aerosol model and the continental model,which used to retrieve the AOD from the POLDER/PARASOL data from 2008 to 2009 in this study area.In addition,the accuracy of AOD retrieved by two aerosol models was verified using the AERONET ground-based measurements.The results indicated that the accuracy of AOD retrieved by the self-defined aerosol model was higher than that by the continental model.The correlation coefficient(R)and root mean squared error(RMSE)of the AOD retrieved by the self-defined aerosol model was 0.75 and 0.20,respectively.While the R and RMSE of the AOD retrieval by the continental model is 0.41 and 0.34,respectively.Therefore,the volume percentages of the aerosol components based on ground measurements have high accuracy and reliability that contribute to improving the retrieval accuracy of AOD.