A new approach to retrieval of aerosol size distributions and integral properties from SAGE II aerosol extinction spectra

Abstract

A new approach to the retrieval of aerosol size distributions and integral properties from Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction spectra is proposed. This method assumes that the aerosol size distribution can be approximated by a histogram of number density as a function of particle size. The retrieved number density in each bin is expressed as a linear combination of the SAGE II aerosol extinctions at four or fewer wavelengths. The coefficients in the weighted linear combination are obtained by minimizing the retrieval error averaged for a set of testing size distributions. The same method has been applied to retrieve aerosol surface area and volume densities from SAGE II aerosol extinctions. The retrieval accuracy was studied by calculating the aerosol surface area and volume densities for six aerosol size distributions retrieved by using the proposed linear minimizing error method. In general, the retrieval error increases with the decreasing number of wavelength‐dependent extinction measurements available for retrieval. Besides accuracy, the proposed method has the advantage of not requiring an initial guess or a weighting function. Furthermore, it is very simple and fast. Another advantage is that the proposed method can still be applied to the case when the number of reliable aerosol extinction is less than four. The formulas presented in this paper can be used easily by investigators to retrieve surface area and volume densities from SAGE II aerosol extinction spectra at different altitudes for a variety of purposes. The proposed new method can also be extended to retrieve properties from other remote sensing systems. The application of the proposed method for instrument design is discussed.