Role of the scattering phase function in the remote sensing of non-spherical dust aerosols

Abstract

The effects of differences between the angular scattering structures of the spherical and the spheroidal scattering phase functions (SPFs) were studied and shown to be significant in radiative transfer calculations and for remote sensing for Asian dust aerosols. We used a discrete ordinate radiative transfer (DISORT) code to estimate the effects of different SPFs with a radiance identical to that for satellite retrieval of dust aerosols. Estimated errors due to the use of SPFs of spherical particles and the use of Henyey-Greenstein (H-G) approximation functions for dust aerosols are substantial. The variability of the resulting remote sensing reflectance was in the range 10 to 70% for the backward-scattering region, suggesting that dust aerosols cannot be treated as spheres because the dust reflectance is strongly affected by the scattering angle. In the case study of moderate resolution imaging-spectroradiometer (MODIS)-retrieved aerosol optical thickness (AOT) during the Asian dust storm day of May 1, 2011, the use of an SPF for spheroidal particles with 256 Legendre polynomial expansion (LPE) terms produced the smallest error whereas the largest errors occurred for the cases of a spherical-particle SPF with 32 LPE terms. These results imply that nonspherical dust aerosols have a large impact on the radiative transfer and that accurate information about the SPF may help reduce errors in both radiative transfer calculations and satellite remote sensing of Asian dust.