Intercomparison of aerosol extinction measured by Stratospheric Aerosol and Gas Experiment (SAGE) II and III

Abstract

Stratospheric Aerosol and Gas Experiment (SAGE) II and SAGE III are two satellite experiments designed to monitor aerosol extinction and the concentration of trace gases in the atmosphere using the solar and/or lunar occultation technique. While SAGE III used nine aerosol channels, four of them were centered at wavelengths very close or equal to the four aerosol channels used by SAGE II. Since both satellites conducted measurements between 2002 and 2005, there are comparison opportunities when their measurement locations on the same day are nearly coincident. In this study, the coincidence events are identified, and the aerosol extinction coefficients, color ratios (ratio of the extinction at two wavelengths), and optical depths measured by both satellites are compared. It is found that in the main stratospheric aerosol layer, between about 18 and 26 km, the differences of extinction coefficients are generally within their measurement uncertainties and are less than about 30%. The discrepancy between the wavelength dependence of the aerosol extinction coefficient, color ratio, and optical depth measured by SAGE II and SAGE III is also discussed. In the main stratospheric aerosol layer, the SAGE III mode radius deduced from the color ratio is about 20 to 30% less than the SAGE II mode radius. Wavelength dependence biases of the aerosol extinction coefficient evident in prior releases of SAGE III data persist in version 4.00.