A new approach to retrieve aerosol optical thickness from AATSR over land

In this paper, an innovative method for simultaneous retrieval of AOT at 0.55 and 0.66 mum from advanced along-track scanning radiometer (AATSR) TOA radiance is presented which exploits multi-spectral and dual-angle view capabilities, based on the fact that the consistent angular dependence of reflectance exists in a certain spectrum and is invariable with wavelength. No assumptions are required about the land surface spectral properties, thus allowing for quantitative regional mapping of aerosol over virtually arbitrary land surface. This study uses the dual-angle 0.55-, 0.66-, and 1.6 mum channel data from the AATSR on board ENVISAT to retrieve AOT over bright land like acrid, semi-acrid areas, and urban areas. Validation was performed over Beijing of China against AErosol RObotic NETwork (AERONET) ground-based sun-photometer data, which shows good agreement between the AATSR-derived estimates of AOT and the sun-photometer measurements. Pearson´s correlation coefficient, r², are 0.81 and 0.83 at nadir and forward view, respectively for 0.55 mum and 0.88 and 0.81 for 0.66 mum for 22 cases combined. Moreover, the algorithm is applied at region scales, thus resulting in AOT maps covering Beijing, demonstrating the great potential over bright land surface at global scales for atmosphere correction and as important climate model input parameters.