Retrieval of Aerosol Optical Properties Based on the Spheroid Model

The Skyrad software package (SKYRAD.pack), which is used to analyze sky radiometer data, utilizes aerosol retrieval algorithms that are based on the Mie theory. In modeling the optical properties of dust-like aerosols, however, it is necessary to account for particle nonsphericity. We applied aerosol retrieval algorithms based on the spheroid model to SKYRAD.pack. We tested the model using simulated data from aerosol models and verified that dust-like aerosol optical properties can be accurately retrieved using the spheroid model. Moreover, we analyzed sky radiometer data collected in Tsukuba, Japan, in April 2006. The results demonstrate that when the diffuse sky flux normalized by the direct flux is used, i.e., the aerosol optical thickness is unknown, the spheroid model can retrieve aerosol optical properties more accurately than the sphere model in the analysis of observations in the case of Asian dust. Furthermore, if solar calibration constants can be determined, aerosol optical properties can be accurately retrieved in both the case based on the Mie theory and the case based on the spheroid model.