Diffuse light corrections to Sun photometry of desert dust and marine aerosols

The NASA Ames airborne Sun photometry program has benefited in many ways from the work of John Reagan. Our water vapor retrieval methods are based on methods published by Prof. Reagan (1987). Designs for our existing instruments and advanced concepts have been influenced by Prof. Reagan´s instruments and by his specialized consulting. And our measurements of the Pinatubo volcanic stratospheric aerosol include corrections for diffuse light effects derived by Prof. Reagan and colleagues. The work described here extends Sun photometric diffuse light correction methods to include conditions influenced by the large particles present in airborne desert dust and marine aerosols. Features of the work include parametric equations that easily determine aerosol optical depth (AOD) correction factors from Ångström exponents of uncorrected AOD spectra. The parametric equations are derived from results of an analytical expression that accounts for all orders of scattering. Aerosol scattering phase functions are derived from a representative range of dust and marine aerosols with realistic size distributions, compositions (or complex refractive indices), and shapes. This aerosol information is obtained from a wide range of retrievals from the AERONET network of Sun-sky radiometers, as well as airborne in situ measurements especially designed to account for large particles.