Accuracy Assessment of Aerosol Optical Depth Retrieved from the Solar Radiance Measurements in North China

By use of automatic sun-tracking photometer CE-318 observations in 2006 measured at the Xilinhot Observatory in Inner Mongolia, a study is performed of variation in atmospheric Aerosol Optical Depth (AOD) retrieved from the solar radiance, concerning the effective factors such as calibration coefficient and cloud. The variation in calibration coefficient decreased more than 18% from January 6, 2006 to January 7, 2007 using Langley calibration method, so the exponential interpolation is adopted to get the value for each month which leads to better retrieval accuracy especially during clear weather. Combining with visibility meter observations, a power-law relation between atmospheric visibility and AOD is figured out for local sandy weather. Based on it, AOD calculated from the atmospheric visibility is studied. Results show that 1) AOD daily variation for clear weather in Xilinhot is unimodal by and large, with a peak in the middle of the day, 2) maximum values of AOD throughout the year appear in spring, with the secondary peak in autumn, 3)a large number of valid data are missing in summer because of the effect by cloud radiance, 4) based on the function relationship suggested, AOD calculated from the atmospheric visibility of dusty weather is more consistent with the real facts while photometer observations are influenced by cloud, the result leading to better precision of dust storms monitoring and pre-warning.