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  • 1
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    Direct and indirect methods for correcting the aerosol effect on remote sensing (1994)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: Aspects of aerosol studies and remote sensing are reviewed. Aerosol scatters solar radiation before it reaches the surface and scatters and absorbs it again after it is reflected from the surface and before it reaches the satellite sensor. The effect is spectrally and spatially dependent. Therefore atmospheric aerosol (dust, smoke and air pollution particles) has a significant effect on remote sensing. Correction for the aerosol effect was never achieved on an operational basis though several case studies were demonstrated. Correction can be done in a direct way by deriving the aerosol loading from the image itself and correcting for it using the appropriate radiative transfer model or by an indirect way, by defining remote sensing functions that are less dependent on the aerosol loading. To some degree this was already achieved in global remote sensing of vegetation where a composite of several days of NDVI (Normalized Difference Vegetation Index) measurements, choosing the maximal value, was used instead of a single cloud screened value. The Atmospheric Resistant Vegetation Index (ARVI) introduced recently for the NASA Earth Observing System EOS-MODIS is the most appropriate example of indirect correction, where the index is defined in such a way that the atmospheric effect in the blue spectral channel cancels to a large degree the atmospheric in the red channel in computations of a vegetation index. Atmospheric corrections can also use aerosol climatology and ground based instrumentation.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: CNES, Proceedings of 6th International Symposium on Physical Measurements and Signatures in Remote Sensing; p 7-19
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  • 2
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    A satellite view of aerosols in the climate system (2002)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Anthropogenic aerosols are intricately linked to the climate system and to the hydrologic cycle. The net effect of aerosols is to cool the climate system by reflecting sunlight. Depending on their composition, aerosols can also absorb sunlight in the atmosphere, further cooling the surface but warming the atmosphere in the process. These effects of aerosols on the temperature profile, along with the role of aerosols as cloud condensation nuclei, impact the hydrologic cycle, through changes in cloud cover, cloud properties and precipitation. Unravelling these feedbacks is particularly difficult because aerosols take a multitude of shapes and forms, ranging from desert dust to urban pollution, and because aerosol concentrations vary strongly over time and space. To accurately study aerosol distribution and composition therefore requires continuous observations from satellites, networks of ground-based instruments and dedicated field experiments. Increases in aerosol concentration and changes in their composition, driven by industrialization and an expanding population, may adversely affect the Earth's climate and water supply.
    Keywords: Meteorology and Climatology
    Type: Nature (ISSN 0028-0836); Volume 419; 6903; 215-23
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  • 3
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    Model simulations of the competing climatic effects of SO2 and CO2 (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Sulfur dioxide-derived cloud condensation nuclei are expected to enhance the planetary albedo, thereby cooling the planet. This effect might counteract the global warming expected from enhanced greenhouse gases. A detailed treatment of the relationship between fossil fuel burning and the SO2 effect on cloud albedo is implemented in a two-dimensional model for assessing the climate impact. Using a conservative approach, results show that the cooling induced by the SO2 emission can presently counteract 50 percent of the CO2 greenhouse warming. Since 1980, a strong warming trend has been predicted by the model: 0.15 C during the 1980-1990 period alone. The model predicts that by the year 2060 the SO2 cooling reduces climate warming by 0.5 C or 25 percent for the Intergovernmental Panel on Climate Change (IPCC) business as usual (BAU) scenario and 0.2 C or 20 percent for scenario D (for a slow pace of fossil fuel burning). The hypothesis is examined that the different responses between the Northern Hemisphere and the Southern Hemisphere can be used to validate the presence of the SO2-induced cooling.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Climate (ISSN 0894-8755); 6; 7; p. 1241-1252.
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  • 4
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    Effect of Amazon smoke on cloud microphysics and albedo - Analysis from satellite imagery (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The effect of smoke aerosol particles on the properties of low cumulus and stratocumulus clouds is studied on the basis of NOAA AVHRR images taken over the Brazilian Amazon Basin during the biomass burning season of 1987. The reflectance at a wavelength of 0.64 micron and the drop size, derived from the cloud reflectance at 3.75 microns, is studied for tens of thousands of clouds. It is shown that the presence of dense smoke can reduce the remotely sensed drop size of continental cloud drops from 15 to 9 microns. Due to both the high initial reflectance of clouds in the visible part of the spectrum and the presence of graphitic carbon, the average cloud reflectance at 0.6 micron is reduced from 0.71 to 0.68 for an increase in smoke optical thickness from 0.1 to 2.0. High concentration of aerosol particles is shown to cause a decrease in the cloud-drop size, and smoke is found to darken the bright Amazonian clouds.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Applied Meteorology (ISSN 0894-8763); 32; 4; p. 729-744.
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  • 5
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    Calibration of the AVHRR visible and near IR channels using radiances measured over remote ocean areas (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An inflight absolute calibration method has been adapted and applied to channel 1 of the AVHRR. The approach is based on AVHRR observations in channels 1, 2 and 4. A rigorous cloud screening is performed, based on the homogeneity of the data in channel 1 and 2 and on the temperature in channel 4. In a combined approach, the off-nadir view satellite count in channel 2 is used to detect the aerosol optical thickness and loading and the count of channel 1 is used to calibrate this channel, based on the predictable Rayleigh scattering component. Water vapor data are used, and the channels are intercalibrated using the ratio between channels 1 and 2 over the glint region.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: In: IGARSS '92; Proceedings of the 12th Annual International Geoscience and Remote Sensing Symposium, Houston, TX, May 26-29, 1992. Vol. 1 (A93-47551 20-43); p. 9-11.
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  • 6
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    Aerosol optical thickness and atmospheric path radiance (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Simultaneous measurements from the ground of the spectral optical thickness and the atmospheric path radiance from over 30 sites located in many parts of the world and affected by several different aerosol types are reported. These measurements are used to derive the relationship between the optical thickness and the path radiance for a single viewing and illumination geometry and to discuss its implications on remote sensing observations. It is shown that simple measurements performed from the ground can yield empirical relationships that can be used to check some of the common but not validated assumptions about the particle homogeneity, sphericity, composition, and size distribution used in remote sensing models and in estimates of the radiative effects of aerosol. The results are used to test concepts of atmospheric corrections and remote sensing of aerosol from space.
    Keywords: METEOROLOGY AND CLIMATOLOGY
    Type: Journal of Geophysical Research (ISSN 0148-0227); 98; D2; p. 2677-2692.
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  • 7
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    Optical properties of aerosol emissions from biomass burning in the tropics, BASE-A (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Ground-based and airborne measurements of biomass-burning smoke particle optical properties, obtained with a view to aerosol-absorption properties, are presented as a function of time and atmospheric height. The wavelength dependence of the optical thickness can be explained by a log-normal size distribution, with particles' effective radius varying between 0.1 and 0.2 microns. The strong correlation noted between aerosol particle profile and CO profile indicates that smoke particulates constitute a good tracer for emission trace gases from tropical biomass burning.
    Keywords: GEOPHYSICS
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  • 8
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    Characteristics of smoke emissions from biomass fires of the Amazon region - BASE-A experiment (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The Biomass Burning Airborne and Spaceborne Experiment-Amazonia was designed for study of both aerosol and gaseous emissions from fires using an airborne sampling platform. The emission factors for combustion products from four fires suggest that the proportion of carbon released in the form of CO2 is higher than for fires of logging which has been burned in the western U.S. Combustion efficiency was of the order of 97 percent for the Amazonian test fire and 86-94 percent for deforestation fires. The inorganic content of particles from tropical fires are noted to be different from those of fires in the U.S.
    Keywords: ENVIRONMENT POLLUTION
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  • 9
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    Atmospherically Resistant Vegetation Index (ARVI) for EOS-MODIS (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: ARVI, which is here proposed as a tool for the remote sensing of vegetation by the EOS MODIS sensor, takes advantage of the presence of the blue channel in MODIS, together with the red and near-IR channels composing the normalized-difference vegetation index (NDVI). Unlike the NDVI, ARVI resists atmospheric effects via a self-correction process for the effects of the atmosphere on the red channel. ARVI is presently shown to have a dynamic range similar to NDVI's, but is on average less sensitive to atmospheric effects by a factor of 4. A single combination of the blue and red channels in the ARVI may be used in all or most remote-sensing applications.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 2, Ma
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  • 10
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    Remote sensing of water vapor in the near IR from EOS/MODIS (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Consideration is given to the selection of spectral channels in the near-infrared IR which are to be employed for the derivation of total column water vapor using the MODIS instrument on the NASA's Earth Observing System. Data obtained show that the three near-IR water vapor channels on the MODIS instrument enable remote sensing of the total column water vapor with an absolute accuracy of +/- 13 percent. An absolute accuracy of +/-7 percent can be obtained if additional MODIS channels are used to decrease the effect of uncertainty in the spectral reflectance of the surface, subpixel clouds, haze, and temperature profile on the derived water vapor.
    Keywords: EARTH RESOURCES AND REMOTE SENSING
    Type: IEEE Transactions on Geoscience and Remote Sensing (ISSN 0196-2892); 30; 5; p. 871-884.
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