Optically thin cirrus cloud contamination in sun photometer data

Abstract

Cloud-related retrieval and contextual biases are important for passive radiance measurements by satellite-based and ground-based remote sensing technologies. Such biases can be more prevalent in Southeast Asia, which experiences frequently overcast skies with persistent thin cirrus and low clouds, mixed with aerosols from industrial pollution and seasonal biomass burning. In this study, we investigate the extent of optically thin cirrus cloud contamination within Aerosol Robotic Network (AERONET) Sun photometer data in Singapore, which is analogous to the difficulties encountered in aerosol optical depth (AOD) retrievals by the MODerate Resolution Imaging Spectroradiometer (MODIS) over Southeast Asia. The AERONET Level 1.5 AOD near real-time cloud-screened data were analyzed from October 2009 to August 2010 with concurrent measurements by a collocated Micro Pulse Lidar (MPL) and sky dome images taken by a Total Sky Imager. Thin cirrus clouds were detected in 17.6 % of AERONET Level 1.5 AOD data with concurrent MPL retrievals. The physical and optical properties of such thin cirrus clouds are also discussed.