Inference of aerosol size distribution surface area density and volume density from multispectral extinction measurements

摘要

Abstract: The Stratospheric Aerosol and Gas Experiment (SAGE) III is planned to be launched in summer 1998. It will provide aerosol extinction coefficients from solar occultation measurements at more wavelengths than SAGE II. This paper describes two methods used for the retrieval of some aerosol characteristics of great interest for the climate modeling and for the study of heterogeneous chemistry: effective radius, effective variance, surface area density and volume density. The first technique consists in a King inversion scheme and the second relies on a least squares fit on the extinction measurements. The two methods are applied to simulated extinction measurements at SAGE III wavelengths to investigate the ability of retrieving the aerosol characteristics in case of unimodal or bimodal log-normal size distributions. The contribution of channel 1.550 micrometer is estimated and uncertainties are also determined. The results derived from the two techniques are consistent in unimodal and bimodal cases for the four quantities: the least squares fit method is much faster but leads to larger uncertainties, in bimodal case the King method allows a better retrieval. !10