RETRIEVAL METHOD FOR OPTICAL THICKNESS OF AEROSDS OVER BEIJING AND ITS VICINITY BY USING THE MODIS DATA

Inversion particles originate from man-made sources such as industrial activities, biomass burning associated with land use processes, wind-blown dust, and natural sources. Those particles affect the climatic change and air pollution significantly. Over big urban area, such as Beijing, man-made inversions is main air pollution materials. For studying urban air-pollution, we hope to obtain inversion product from high distribution satellite data. MODIS was developed as a facility instrument for the Earth Observing System (EOS) launched in 1999 on Terra. It provides images in 36 spectral bands between 0.415 μm and 14.235 μm with spatial resolutions of 250, 500, 1000 m. MODIS provides high quality data for obtaining inversions optical thickness. Retrieval inversions optical thickness over Beijing and it's surrounding area from MODIS data aimed at providing a new, economical and convenient measurement for urban air pollution monitoring. Based on the 6S radiative transfer code, the dense dark vegetation method and contrast reduction method of estimating the optical thickness over land surface from EOS-Terra/MODIS data at wavelengths of 0.66 μm and 0.47 μm were used to retrieve the optical thickness of inversions over Beijing and its surrounding area. The opticalt hickness of inversions estimated from the sun photometer on the ground at the same time as the pass of the satellite was used to validate the retrieval from satellite data. The way to select the best combination of method, satellite channel and inversion model has been given, which could obtain the reasonable inversions optical thickness. In the retrieval calculation, there were four kinds of inversion model supplied for remote sensing of inversion optical thickness. In the study, wefind that the dense dark vegetation method fails to obtain inversion optical thickness over urban area because of bright surface and strongly absorbing urban inversion type. The same error in inversion model would lead to the oppositional result error direction (positive or negative), which causes respectively by the two methods. Aerosol optical thickness distribution from MODIS data shows that its large values are often found in Shijiazhuang, Beijing, and Tianjing areas.