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Introduction |
What does it mean to use MODIS retrievals consistently? |
Estimating Aerosol Radiative Effect |
Results
Estimating Aerosol Radiative effect
The aerosol effect is the difference in radiative flux at top of the atmosphere between an atmosphere with aerosol and an atmosphere with no aerosol. Radiative flux is not the same as satellite-observed reflectances. Reflectances are measured at a specific angle and wavelength. Flux is integrated over all angles and for the entire solar spectrum.
Remer and Kaufman use a radiative transfer model (CLIRAD-SW) to model the radiative flux. Model inputs are based on the 9 MODIS aerosol modes. The model is run both with aerosol optical thickness (a measure of light extinction) and for an atmosphere with no aerosol. The difference in these two runs is the radiative effect. The satellite observes the scene, once per day, providing instantaneous aerosol conditions. Values of aerosol effect based on instantaneous conditions are normalized to provide the 24 hour average. The figure shows calculated 24-hour aerosol radiative effect for a variety of aerosol loadings for each of the 9 aerosol modes of the MODIS retrieval.
Each MODIS observation provides two chosen modes, the relative weight between them and the aerosol optical thickness. Thus, all that Remer and Kaufman had to do was use the calculations represented by the figure with the MODIS retrievals of modes and aerosol optical thickness to provide the aerosol effect. The aerosol effect was calculated over the global oceans in 13 sections using MODIS data that span the time from September 2001 to October 2004.
Daily averaged aerosol radiative effect for a 12 hour day with the solar zenith angle equal to 0 at noon, a variety of aerosol optical thicknesses and the nine modes of the MODIS aerosol retrieval over ocean.
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Introduction |
What does it mean to use MODIS retrievals consistently? |
Estimating Aerosol Radiative Effect |
Results
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