Improved retrieval of aerosol size-resolved properties from moderate resolution imaging spectroradiometer over India: role of aerosol model and surface reflectance

Abstract

We have compared the total as well as fine mode aerosol optical depth (τ and τ_fine) retrieved by Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra and Aqua (2001–2005) with the equivalent parameters derived by Aerosol Robotic Network (AERONET) at Kanpur (26.45°N, 80.35°E), northern India. MODIS Collection 005 (C005)–derived τ_0.55 was found to be in good agreement with the AERONET measurements. The τ_fine and η (τ_fine/τ) were, however, biased low significantly in most matched cases. A new set of retrieval with the use of absorbing aerosol model (SSA ∼ 0.87) with increased visible surface reflectance provided improved τ and τ_fine at Kanpur. The new derivation of η also compares well qualitatively with an independent set of in situ measurements of accumulation mass fraction over much of the southern India. This suggests that though MODIS land algorithm has limited information to derive size properties of aerosols over land, more accurate parameterization of aerosol and surface properties within the existing C005 algorithm may improve the accuracy of size-resolved aerosol optical properties. The results presented in this paper indicate that there is a need to reconsider the surface parameterization and assumed aerosol properties in MODIS C005 algorithm over the Indian region in order to retrieve more accurate aerosol optical and size properties, which are essential to quantify the impact of human-made aerosols on climate.