A Shortcut from Broadband to Spectral Aerosol Optical Depth

Martin Kannel ； Hanno Ohvril ； Oleg Okulov

《Proceedings of the Estonian Academy of Sciences》 61卷4期 (2012/12) Pp. 266-278

並列摘要

The concept behind the shortcut idea is a close correlation between column broadband aerosol optical depth (BAOD) and aerosol optical depth at 500 nm (AOD500). The method uses only two input parameters: (a) the Bouguer broadband coefficient of column transparency for optical mass m = 2 (solar elevation about 30°) and (b) integrated column precipitable water vapour which can be roughly estimated using surface water vapour pressure. In creating the method, a large database, including almost 20000 complex, spectral and broadband direct solar beam observations at Tõravere, Estonia, during all seasons of a 8-year period, 2002-2009, was used. The AOD500 observations were performed by the NASA project AERONET and the broadband direct beam ones by the Estonian Meteorological and Hydrological Institute. Analysis of this database revealed a high correlation between BAOD and AOD500 which enabled transition from broadband to spectral AOD. Almost 82% of the observations in the database belonged to lower turbidities when AOD500 ＜ 0.2. The root mean square deviation (RMSD) for AOD500 prediction in this range was 0.022. For AOD500 = 0.2-0.4, the RMSD was 0.035, for 0.4-0.6, the RMSD was 0.042. Relative RMSD for these ranges was about 22%, 12%, and 9%, respectively. For AOD500 ＞ 0.6, relative RMSD remained 9%. For comparison, the same database was used to test Gueymard's broadband parameterization based on his SMARTS2 classic model. The last one, apparently due to problems with circumsolar radiation, slightly but systematically underestimated the AOD500. However, there was a close correlation between our shortcut results and Gueymard's broadband parameterization.

並列關鍵字

AERONET ； aerosols ； aerosol optical depth ； light attenuation ； atmospheric integral transparency coefficient ； broadband direct irradiance