Atmospheric aerosol play an important role in the climate change, though direct and indirect processes1. To evaluate the effects of aerosols on climate it is necessary to estimate their spatial and temporal distributions2. Since 2000, the Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) have been providing global aerosol products3. However, the uncertainties still exist in current satellite aerosol products attributable to the complex surface, cloud contamination, and aerosol models used in the retrieving process5. Comparing to AERONET AOD, the larger magnitude and different variation tendency in AOD for both sensors indicate that either individual aerosol product may not be good application over China. Combing multiple sensors is a method to reduce uncertainties and improve observational accuracy. An adaptive weighted estimate algorithm of multi-sensor data fusion was presented, which could adjust the fused sensor’s weight in time according to the variation in sensor’s variance. The combined AOD product using the fusion method is in better agreement with corresponding AOD from AERONET than single sensor, which illustrate the fusion method performs better applicability in China. The fusion method can reduce uncertainties both sensors and expand the scope of the distribution in AOD. Using the latest ten-year (2002-2010) fusion product, we study the trend analysis of the aerosol optical depth over typical regions in China. The increasing trend is found over Jingjintang and Yangtze River Delta, which are highly associated with human activities.
The analysis of the spatial–temporal variability and trends of aerosols over China based on ∼11 years (February 2000 to December 2010) of Terra-Multiangle Imaging SpectroRadiometer (MISR) Level 3 aerosol products is the focus. The study shows that the MISR aerosol optical depth (AOD) is in good agreement with corresponding AOD from AERONET stations and suggests that MISR aerosol products have higher applicability compared with MODIS AOD products over China. The spatial–temporal distribution and trends for annual and seasonal AOD values over the middle and eastern regions of China are the main focus. The results of our analysis show the significant characteristics and seasonal variation of the aerosol distribution over the study areas. The seasonal distribution in AOD over the study areas is not consistent with the MODIS data. An insignificant trend (5.3%) is observed over the whole study area during the study period. The larger positive tendencies are found in the Yangtze River Delta and the Pearl River Delta (PRD); the values increased by 24.4% and 18% and are considered to be significant with a confidence level of >95% . However, in contrast to the recently reported negligible AOD trends of 0.002 per decade using MODIS data over Sichuan, significant increasing trends of 0.046 per 11 years for MISR over the same areas have been measured. The analysis of seasonal variation revealed the seasonal trend in the AOD and the main types of aerosols. During spring, the largest increasing trend (30.2%) is observed in the PRD with a stable composition of fine and coarse aerosols. A pronounced decreasing trend is found over Shanxi and decreased by −18.7% in spring during the period, which has not been previously reported. MODIS-Terra currently shows artificial negative AOD trends over land. Therefore, trends derived from MODIS-Terra may not reflect the realistic decadal aerosol changes and variability. The study shows that seasonal distribution and trend analyses are inconsistent when using MISR AOD products and MODIS AOD products over study areas, which indicates that the analysis of aerosol variation using MISR sensors is necessary.
Aerosols are one of the most important parameters affecting the Earth's energy balance and hydrological cycle1. They
can arouse uncertainties effects on climates. To narrow the uncertainties associated with the direct and indirect aerosol
effects on climates, the spatial-temporal properties of aerosol over China are investigated using the radiance
measurements performed by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on board the
Terra and Aqua satellites from 2002 to 2010. The most prominent variational regions are the northern, eastern China.
The high AOD values occur in 2004, 2006 and 2007 year, respectively. The tendencies of AOD are in good agreement
with corresponding AOD tendencies based on data from Aerosol Robotic Network (AERONET) stations in the study
regions2. Seasonal AOD maxima are obtained in spring (March to May) and summer (June to August) seasons, due to
large humidity and biomass burning, respectively. Dust activities in spring are frequent occurrences that also lead to high
aerosol loading. AOD minima are obtained in winter (December to February) seasons. The result of our analysis reveal
significant trend of seasonal AOD in the Northern and Southern China.
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