Evaluation of Optical Properties of Atmospheric Aerosols Estimated from Ground-based Polarization Measurements

Polarization measurements of the sky radiation have been carried out at the ground station in the Kanazawa city, Japan in the spring season. The multi-spectral polarimeter, PSR-1000, developed by opt research corporation, Japan has been used. The polarized intensity was measured at angles of 75, 90, 105 and 120 degrees from the solar direction in the principal plane. Polarization measurements of light ray reflected by the ground surface were also made. First of all, it is shown that degrees of polarization decrease uniformly as the wavelength is longer when the hazy Asian dust was recognized in the Kanazawa city. It is also shown that degrees of polarization of the reflected light by the ground surface such as the asphalt concrete are not so much low. Next, a new method for estimating optical properties of Asian dust such as the optical thickness, number size distribution, refractive index, and ground reflectance from the measured polarization is described. This method was applied to polarization data acquired on April 13 and 27, 2003. Finally, the estimated optical thickness of Asian dust at 490 nm was compared with the optical thickness of aerosols measured at 500 nm by the sun photometer to evaluate the proposed estimation algorithm.