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  • 1
    Publication Date: 2019-07-12
    Description: The seasonal and spatial varability of Aerosol Above Cloud (AAC) properties are derived from passive satellite data for the year 2008. A significant amount of aerosols are transported above liquid water clouds on the global scale. For particles in the fine mode (i.e., radius smaller than 0.3 m), including both clear sky and AAC retrievals increases the global mean aerosol optical thickness by 25(+/- 6%). The two main regions with man-made AAC are the tropical Southeast Atlantic, for biomass burning aerosols, and the North Pacific, mainly for pollutants. Man-made AAC are also detected over the Arctic during the spring. Mineral dust particles are detected above clouds within the so-called dust belt region (5-40 N). AAC may cause a warming effect and bias the retrieval of the cloud properties. This study will then help to better quantify the impacts of aerosols on clouds and climate.
    Keywords: Environment Pollution; Meteorology and Climatology
    Type: GSFC-E-DAA-TN10642
    Format: application/pdf
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  • 2
    Publication Date: 2019-07-13
    Description: This work provides a comparison of satellite retrievals of Saharan desert dust aerosol optical depth (AOD) during a strong dust event through March 2006. In this event, a large dust plume was transported over desert, vegetated, and ocean surfaces. The aim is to identify the differences between current datasets. The satellite instruments considered are AATSR, AIRS, MERIS, MISR, MODIS, OMI, POLDER, and SEVIRI. An interesting aspect is that the different algorithms make use of different instrument characteristics to obtain retrievals over bright surfaces. These include multi-angle approaches (MISR, AATSR), polarisation measurements (POLDER), single-view approaches using solar wavelengths (OMI, MODIS), and the thermal infrared spectral region (SEVIRI, AIRS). Differences between instruments, together with the comparison of different retrieval algorithms applied to measurements from the same instrument, provide a unique insight into the performance and characteristics of the various techniques employed. As well as the intercomparison between different satellite products, the AODs have also been compared to co-located AERONET data. Despite the fact that the agreement between satellite and AERONET AODs is reasonably good for all of the datasets, there are significant differences between them when compared to each other, especially over land. These differences are partially due to differences in the algorithms, such as assumptions about aerosol model and surface properties. However, in this comparison of spatially and temporally averaged data, it is important to note that differences in sampling, related to the actual footprint of each instrument on the heterogeneous aerosol field, cloud identification and the quality control flags of each dataset can be an important issue.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC-E-DAA-TN9219 , Atmospheric Measurement Techniques (ISSN 1867-1381); 5; 8; 1973-2002
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-13
    Description: This work provides a comparison of satellite retrievals of Saharan desert dust aerosol optical depth (AOD) during a strong dust event through March 2006. In this event, a large dust plume was transported over desert, vegetated, and ocean surfaces. The aim is to identify and understand the differences between current algorithms, and hence improve future retrieval algorithms. The satellite instruments considered are AATSR, AIRS, MERIS, MISR, MODIS, OMI, POLDER, and SEVIRI. An interesting aspect is that the different algorithms make use of different instrument characteristics to obtain retrievals over bright surfaces. These include multi-angle approaches (MISR, AATSR), polarisation measurements (POLDER), single-view approaches using solar wavelengths (OMI, MODIS), and the thermal infrared spectral region (SEVIRI, AIRS). Differences between instruments, together with the comparison of different retrieval algorithms applied to measurements from the same instrument, provide a unique insight into the performance and characteristics of the various techniques employed. As well as the intercomparison between different satellite products, the AODs have also been compared to co-located AERONET data. Despite the fact that the agreement between satellite and AERONET AODs is reasonably good for all of the datasets, there are significant differences between them when compared to each other, especially over land. These differences are partially due to differences in the algorithms, such as as20 sumptions about aerosol model and surface properties. However, in this comparison of spatially and temporally averaged data, at least as significant as these differences are sampling issues related to the actual footprint of each instrument on the heterogeneous aerosol field, cloud identification and the quality control flags of each dataset.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC.JA.6605.2012 , Atmospheric Measurement Techniques Discussions; 5; 1; 697-746
    Format: application/pdf
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  • 4
    Publication Date: 2019-07-13
    Description: The proposed development is an attempt to enhance aerosol retrieval by emphasizing statistical optimization in inversion of advanced satellite observations. This optimization concept improves retrieval accuracy relying on the knowledge of measurement error distribution. Efficient application of such optimization requires pronounced data redundancy (excess of the measurements number over number of unknowns) that is not common in satellite observations. The POLDER imager on board the PARASOL microsatellite registers spectral polarimetric characteristics of the reflected atmospheric radiation at up to 16 viewing directions over each observed pixel. The completeness of such observations is notably higher than for most currently operating passive satellite aerosol sensors. This provides an opportunity for profound utilization of statistical optimization principles in satellite data inversion. The proposed retrieval scheme is designed as statistically optimized multi-variable fitting of all available angular observations obtained by the POLDER sensor in the window spectral channels where absorption by gas is minimal. The total number of such observations by PARASOL always exceeds a hundred over each pixel and the statistical optimization concept promises to be efficient even if the algorithm retrieves several tens of aerosol parameters. Based on this idea, the proposed algorithm uses a large number of unknowns and is aimed at retrieval of extended set of parameters affecting measured radiation.
    Keywords: Earth Resources and Remote Sensing
    Type: GSFC.JA.6435.2012 , Atmospheric Measurement Techniques; 4; 975-1018
    Format: application/pdf
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  • 5
    Publication Date: 2016-08-16
    Description: The spatial and temporal variability of the aerosol Single Scattering Albedo (SSA at 865 nm) has been estimated over clear-sky ocean for 2006 by using measurements acquired by POLDER (Polarization and Directionality of Earth Reflectances). Our estimates are correlated with sun-photometer retrievals (R = 0.63). Differences in SSA are generally around 0.05 and systematically fall below 0.055 for optical thicknesses ≥ 0.3 (at 865 nm) and modeling errors ≤ 3.0 %. Fine absorbing aerosols (radius ≤ 0.16 μ m) are detected in many coastal regions. The lowest SSAs are retrieved over the southeast Atlantic during summer (0.80) whereas non-absorbing fine particles (≥ 0.98) are observed over the North Pacific. During winter, fine absorbing aerosols are detected together with mineral dust near the coasts of western Africa (0.90), over the tropical Atlantic (0.88) and around India (0.88). Long–range transport of absorbing species is also detected, as for instance over the Arctic. This study could help to constrain aerosol absorption and radiative forcing in models.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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