Estimation of the temporal and spatial distribution of the optically thin Asian dust from satellite image data

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In general, it is very difficult to identify the widely spread hazy dust cloud in satellite images over the land surface. In this study, a new method for estimating the temporal and spatial distribution of the optically thin Asian dust was developed.(1)Polarization measurements of the sky radiation by the multi-spectral polarimeter have been carried out at the ground station in Kanazawa city, Japan from March to May in 2000 to 2005. In this study, (i) Web application system for retrieving degrees of polarization from the database of polarization measured properly by the polarimeter was made, and (ii) the method for estimating optical properties of Asian dust, such as the optical thickness, the number size distribution and the refractive index, and the ground reflectance from polarization data measured at angles of 75, 90, 105 and 120 degrees from the solar direction in the principal plane was developed.(2)A new algorithm for estimating optical properties of the hazy Asian dust and the ground reflectance simultaneously from ADEOSII/POLDER data over the land surface received at a single channel was developed. In order to evaluate the algorithm, degrees of polarization measured at the ground station are compared with those estimated from ADEOSII/POLDER data on May 3, 2003. As a result, it was found that the values of optical parameters of Asian dust estimated at the 670nm channel provide reasonable ones.(3)In order to estimate the temporal and spatial density distribution of Asian dust over East Asia, the long-range transport simulation model of dust particles was used. The released region and mass flux of Asian dust was determined such that the concentration of Asian dust obtained from the long-range transport simulation is almost equal to that of SPM (Suspended Particulate Matter) measured at various places in Japan.