Verification For The Satellite Remote Sensing Products Of Aerosol Optical Thickness In Taklimakan Desert

Using ground-based Aerosol Optical Depth (AOD) data at Tazhong, Taklimakan Desert, four sets of satellite aerosol data, i.e., multi-angle imaging spectrometer (MISR), Moderate Resolution Imaging Spectrometer (MODIS) and the Ozone Monitoring Instrument (OMI) from 2007 to 2008 were validated. Besides, data from CALIOP are used to investigate the vertical distribution of aerosol. Result from radiative transfer model (SBDART) is also used to compare with OMI/UVAI for sensitivity experiment. The main contents of the study and their primary results are summarized as follows:(1)The correlation coefficient for MODIS/AOD is the largest (0.91), followed by OMI/AOD (0.87), MISR/AOD (0.84) and OMI/UVAI (0.51). MISR/AOD root mean square error (0.14) and the average deviation (-0.06) are the lowest in the four products. MISR/AOD and MODIS/AOD is relatively less than the ground-based AOD, however, OMI/AOD and OMI/UVAI exceed the ground-based ones. Under the same conditions (ground-based AOD is limited to less than 2.0), the root mean square error and the standard deviation of MISR is the lowest. Seasonal variation of aerosol loading is captured by satellite data.(2)Spring and summer AOD is relatively larger and AOD is relatively lower in the autumn and winter. The result of Angstrom exponent reflects that the spring has the minimum(0.11), followed by summer and autumn, and winter has the maximum(0.61), which shows that the aerosol particle is larger in spring and summer while it is smaller in autumn and winter. Besides, Taklimakan belongs to the sand source where aerosol type is single. So in summary, the annual variability tendency of AOD from 2000 to 2010 is not that obvious. The result of the retrieval shows that 2003 has the maximal aerosol contents during the decade, the annual average is up to 0.32, while 2005 has the minimal aerosol contents, the annual average is 0.28.(3) The extinction coefficient decreases with increasing altitude, the atmosphere in the upper troposphere is more clean, and aerosols mainly concentrated in the middle and lower troposphere. The value of the vertical lapse rate in winter is minimum, this attributes to the weak convection resulted from the relative low inversion layer in winter. Tropospheric vertical distribution of aerosol extinction coefficient is characterized by a multi-layer structure which is different from Rayleigh scattering of air molecules that decreases monotonically with increasing height. Large concentration of aerosol exists at 1.5-2 km and 3 km respectively in spring, the aerosol extinction coefficient becomes larger, which reflects the complexity of aerosols' vertical structure.(4)Aerosol Index calculated from SBDART is used for comparison research. The results show that AI is extremely sensitive to the aerosol layer height and they are of almost linear relationship. AI is not sensitive to the boundary layer at 1-2 km,1 km particularly and increases with the aerosol layer height. In addition AI is also very sensitive to the single scattering albedo. Research shows that AI is more sensitive to the change of observation angle, AI decreases with the increasing observation angle, especially when the angle is greater than 15°, the decreasing trend is larger. Because of the narrow scanning width of CALIOP, not all region have the information of aerosol height. So we can get aerosol height in certain areas by simulating experiment.