Research On Retrieval Of Aerosol Optical Depth In Xi’an Area Based On MODIS Data In Recent Ten Years

Ecological destruction and environmental pollution have been becoming more serious as the rapid economy development.The aerosol particulates have been main pollutants affected atmosphere quality.The Aerosol Optical Depth(AOD)can change the radiation balance,influence eco-system,and have a long-term effect on human’s health.However,the limited sites on the ground to monitor environment pollution,can not provide a wide range of continual monitoring timely and reflect the continuous variance of the region.With the rapid development of satellite and remote sensing technology,the AOD retrieved by satellite which has advantage of multi-sensor,multi-resolution,wide range observation and continuity become an important research field,in the same time,it saves a lot of time and cost.Based on the Dark Target and surface reflectance algorithm,the thesis uses MODISL1 B and MOD09A1 data to retrieve the AOD of Xi’an area from 2009 to 2018 with the look-up table and AOD pattern made by meteorological data.The article obtained the following results through research:(1)The research achieves the AOD in Xi’an area from March to November using DT algorithm,as well as AOD in winter which is inversed by surface reflectance algorithm with the reflectance data established by MOD09A1 data in same month.In addition,the author compares the AOD retrieved from image in winter with NASA aerosol products which is MOD04＿L2 data and calculates the correlation coefficient is 0.79 through regression.The research using the DT method that it assumes all the pixels are dark targets,has large influence on the results of retrieved AOD.But the surface vegetation,especially in urban areas in winter,is sparse and the ground surface is regarded as bright pixels.The surface reflectance method,which use the reflectance of each month in latest three years to make the surface reflectance database,has low reflective error and high AOD precision in urban areas while its accuracy is relatively low in dense vegetation region.(2)The research uses PM10 data of AQI ground station to compare with AOD retrieved by satellite image and the correlation coefficient is 0.568,while it turns to be 0.633 after humidity and vertical amendment.The AOD achieved from satellite image,which can make up the deficiency of ground monitoring stations,could monitor the the environment pollution of Xi’an area,reflect the distribution and motivation of AOD,provide some evidence for pollution monitoring and forecast.(3)In the past ten years,the spatial distribution character of AOD in Xi’an is that the AOD is higher in urban areas,but lower in southwest and southeast districts.The AOD season character is spring AOD value is highest while AOD of winter is lowest.Secondly,the research analyses the factors affecting AOD: precipitation,elevation,slope,land cover and NDVI.The trend of precipitation is opposite to that of AOD in some years,that is,when the precipitation become higher,the AOD value is lower.AOD has an obvious negative correlation with elevation,slope and NDVI,in other word,the AOD value in the region where has higher altitude,slope and NDVI,is correspondingly lower.The relationship between land use type and AOD is that the AOD in city and farmland is higher than other regions.