Retrieval and Validation of Atmospheric Aerosol Optical Depth over Land from AVHRR

An algorithm which can be used to retrieve aerosol optical depth (AOD) over land from the Advanced Very High Resolution Radiometer(AVHRR) has been developed. As it is difficult to assess surface reflectance over land for AVHRR unlike the Moderate Resolution Imaging Spectroradiometer(MODIS), the multiple regression method was employed by using collocated MODIS AOD and AVHRR Level1b measurements to generate regression coefficients from May 2003 through December 2011 for the Beijing Area(39 – 42°N; 115 – 118° E).The daily regional mean AOD from AVHRR agrees well with the MODIS product with a correlation coefficient larger than 0.85.The regional monthly mean AOD from AVHRR, MYD04 and MYD08 all have a tendency to be consistent with one another; a correlation coefficient of 0.92 was found. The correlation coefficients were 0.76 in Beijing and 0.83 in Xianghe when AERONET was used to validate the AVHRR AOD retrievals. The distribution pattern of the seasonal mean AOD from AVHRR is consistent with that of MODIS over mainland China area (15 – 45°N; 75 – 135° E) in 2007. According to these encouraging validation results, the multiple regression method offers the potential to generate an AOD climatology data record(CDR) from long term AVHRR data over land.