A Novel Aerosol Load Index Using MODIS Visible Bands: Applied to South-West Part of Iran

Because of the existence of some gaps, uncertainties, and coarse spatial resolution in global aerosol optical depth (AOD) data over south-west part of Iran as the study area, a novel aerosol load index is proposed. As no AERONET station is available in the study area, an index is needed that does not use particle properties. The proposed algorithm has several steps: cloud masking, Rayleigh path reflectance, surface reflectance database, aerosol reflectance, and aerosol load index. Surface reflectance database of 0.05° latitude × 0.05° longitude resolution is calculated by improved minimum reflectance technique (IMRT) for spring season of 2005. The correlation of IMRT surface reflectance at 0.47 μm wavelength with MOD09 is increased in comparison with minimum reflectance technique (MRT), R = 0.75. Aerosol reflectance is obtained through radiation transfer equation, Rayleigh path reflectance, and surface reflectance database. The proposed load index is based on reducing the geometry dependency; hence normalized aerosol reflectance by accounting for solar/view slant path is used. The aerosol load index is verified for dust contamination. The suggested algorithm is applied over study area in spring 2005 using moderate resolution imaging spectroradiometer (MODIS) level L1B calibrated reflectance MOD02Hkm on Terra spacecraft. The spatial resolution of final aerosol load index is 500 m. For validation, the resultant load index is compared with dark-target and Deep Blue retrieved AOD of MOD/MYD04 and correlations of R = 0.82 and R = 0.71 are found at 0.47 μm wavelength, respectively. In comparison with ground base dust particle concentration, correlation of R = 0.72 is achieved correspondingly.