Aerosol optical depths (AODs) from MODIS and MISR onboard the Terra satellite are assessed by comparison with measurements from four AERONET sites located in northern China for the period 2006-2009. The results show t...Aerosol optical depths (AODs) from MODIS and MISR onboard the Terra satellite are assessed by comparison with measurements from four AERONET sites located in northern China for the period 2006-2009. The results show that MISR performs better than MODIS at the SACOL and Beijing sites. For the Xianghe and Xinglong sites, MODIS AOD retrievals are better than those of MISR. Overall, the relative error of the Angstrom exponent from MISR compared with AERONET is about 14%, but the MODIS error can reach 30%. Thus, it may be better to use the MISR Angstrom exponent to derive wavelength-dependent AOD values when calculating the aerosol radiative forcing in a radiative transfer model. Seasonal analysis of AOD over most of China shows two main areas with high aerosol loading: the Taklimakan Desert region and the southern part of North China and northern part of East China. The locations of these two areas of high aerosol loading do not change with season, but the AOD values have significant seasonal variation. The largest AOD value in the Taklimakan appears in spring when the Angstrom exponents are the lowest, which means the particle radii are relatively large. Over North and East China, the highest aerosol loading appears in summer. The aerosol particles are smallest in summer over both high-AOD areas.展开更多
This study presents detailed analysis of spatiotemporal variations and trend of dust optical properties i.e., Aerosol Optical Depth(AOD) and Angstrom component over Asian desert regions using thirteen years of data(i....This study presents detailed analysis of spatiotemporal variations and trend of dust optical properties i.e., Aerosol Optical Depth(AOD) and Angstrom component over Asian desert regions using thirteen years of data(i.e., 2001–2013) retrieved from Aerosol Robotic Network(AERONET), Moderate Resolution Imaging Spectroradiometer(MODIS) and Multi-angle Imaging Spectroradiometer(MISR). These regions include Solar Village, Dunhuang and Dalangzadgad and are considered as origin of desert aerosols in Asia. Mann–Kendall trend test was used to show the trend of AOD. The relationship of AOD with weather parameters and general AOD trend over different wavelengths has also been shown. AOD's trend has been observed significant throughout the year in Solar Village, while in Dunhuang and Dalanzadgad the significant trend has been found only in peak period(March–June).Analysis show high values of AOD and low values of angstrom in Solar Village during peak period. In Chinese desert regions, high values of AOD have been found during peak period and low values in pre-peak period. Significant relationship has been observed between AOD and average temperature in Solar Village and Dalanzadgad whereas rainfall and wind speed showed no significant impact on AOD in all desert regions.展开更多
Deserts,which have high surface albedo and wide area,are important components of the earth system.It is very important for the research of surface radiation and energy balance to understand the anisotropic scattering ...Deserts,which have high surface albedo and wide area,are important components of the earth system.It is very important for the research of surface radiation and energy balance to understand the anisotropic scattering of desert areas.The emergence and development of multi-angle remote sensing made possible the inversion of the anisotropic scattering of desert areas at the regional or global scale.Firstly,this paper explored the accuracy of the inversion of asymmetry factor using the Hapke model and the simulated single-and multi-phase MISR data.Based on the results,the asymmetry factor of representative surface of desert areas in northwestern China was retrieved.The values of the asymmetry factor retrieved from MISR data were compared with the values retrieved from the laboratory data.The results showed that the single-phase MISR data could be used for the inversion of asymmetry parameter of desert areas.The sign of the asymmetry parameter for the laboratory measurements was positive,which suggests that the surface of laboratory samples is forward scattering.The sign of the asymmetry parameter for MISR data was negative;that is,it is backscattering.The values of the asymmetry parameters retrieved from MISR data were related to the character of the land surface.At Loulan,where the surface was smoother than other sites,retrieved values exhibited the largest negative values of asymmetry factor,suggesting the strongest backscattering.The sand dune area of the Kumtag Desert,which has the greatest roughness,had only slightly negative asymmetry factor values.These findings indicated that at the sensor scale,a rough surface(e.g.,dunes) does not necessarily mean more backscattering than a smooth surface.This finding has significant implications for empirical methods(e.g.,using the normalized index of backward-scattered radiance minus forward-scattered radiance as an indicator of surface roughness),which should be used carefully for analyzing surface roughness from the remote sensing data.展开更多
The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satell...The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.展开更多
基金supported by the National Basic Research Program (2012CB955302)the National Natural Science Foundation of China (41105019 and 41175042)+1 种基金the Specialized Research Fund for Doctoral Program of Higher Education (20110211120021)the Fundamental Research Fund for Central Uni versities (lzujbky-2011-4)
文摘Aerosol optical depths (AODs) from MODIS and MISR onboard the Terra satellite are assessed by comparison with measurements from four AERONET sites located in northern China for the period 2006-2009. The results show that MISR performs better than MODIS at the SACOL and Beijing sites. For the Xianghe and Xinglong sites, MODIS AOD retrievals are better than those of MISR. Overall, the relative error of the Angstrom exponent from MISR compared with AERONET is about 14%, but the MODIS error can reach 30%. Thus, it may be better to use the MISR Angstrom exponent to derive wavelength-dependent AOD values when calculating the aerosol radiative forcing in a radiative transfer model. Seasonal analysis of AOD over most of China shows two main areas with high aerosol loading: the Taklimakan Desert region and the southern part of North China and northern part of East China. The locations of these two areas of high aerosol loading do not change with season, but the AOD values have significant seasonal variation. The largest AOD value in the Taklimakan appears in spring when the Angstrom exponents are the lowest, which means the particle radii are relatively large. Over North and East China, the highest aerosol loading appears in summer. The aerosol particles are smallest in summer over both high-AOD areas.
基金supported by the National Natural Science Foundations of China (Nos.41475136 and 41590871)International Science & Technology Cooperation Program of China (No.2013DFG22820)
文摘This study presents detailed analysis of spatiotemporal variations and trend of dust optical properties i.e., Aerosol Optical Depth(AOD) and Angstrom component over Asian desert regions using thirteen years of data(i.e., 2001–2013) retrieved from Aerosol Robotic Network(AERONET), Moderate Resolution Imaging Spectroradiometer(MODIS) and Multi-angle Imaging Spectroradiometer(MISR). These regions include Solar Village, Dunhuang and Dalangzadgad and are considered as origin of desert aerosols in Asia. Mann–Kendall trend test was used to show the trend of AOD. The relationship of AOD with weather parameters and general AOD trend over different wavelengths has also been shown. AOD's trend has been observed significant throughout the year in Solar Village, while in Dunhuang and Dalanzadgad the significant trend has been found only in peak period(March–June).Analysis show high values of AOD and low values of angstrom in Solar Village during peak period. In Chinese desert regions, high values of AOD have been found during peak period and low values in pre-peak period. Significant relationship has been observed between AOD and average temperature in Solar Village and Dalanzadgad whereas rainfall and wind speed showed no significant impact on AOD in all desert regions.
基金supported by National Natural Science Foundation of China (Grant No.40930103)National High-tech Research & Development Programme of China (Grant No.2009AA12Z134)National Natural Science Foundation of China (Grant No.40701125)
文摘Deserts,which have high surface albedo and wide area,are important components of the earth system.It is very important for the research of surface radiation and energy balance to understand the anisotropic scattering of desert areas.The emergence and development of multi-angle remote sensing made possible the inversion of the anisotropic scattering of desert areas at the regional or global scale.Firstly,this paper explored the accuracy of the inversion of asymmetry factor using the Hapke model and the simulated single-and multi-phase MISR data.Based on the results,the asymmetry factor of representative surface of desert areas in northwestern China was retrieved.The values of the asymmetry factor retrieved from MISR data were compared with the values retrieved from the laboratory data.The results showed that the single-phase MISR data could be used for the inversion of asymmetry parameter of desert areas.The sign of the asymmetry parameter for the laboratory measurements was positive,which suggests that the surface of laboratory samples is forward scattering.The sign of the asymmetry parameter for MISR data was negative;that is,it is backscattering.The values of the asymmetry parameters retrieved from MISR data were related to the character of the land surface.At Loulan,where the surface was smoother than other sites,retrieved values exhibited the largest negative values of asymmetry factor,suggesting the strongest backscattering.The sand dune area of the Kumtag Desert,which has the greatest roughness,had only slightly negative asymmetry factor values.These findings indicated that at the sensor scale,a rough surface(e.g.,dunes) does not necessarily mean more backscattering than a smooth surface.This finding has significant implications for empirical methods(e.g.,using the normalized index of backward-scattered radiance minus forward-scattered radiance as an indicator of surface roughness),which should be used carefully for analyzing surface roughness from the remote sensing data.
基金Under the auspices the Fundamental Research Funds for the Central Universities,China(No.2017TD-26)the Plan for Changbai Mountain Scholars of Jilin Province,China(No.JJLZ[2015]54)
文摘The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.