"Regional biases in the retrieved instantaneous reflected short wave flux at the top of the atmosphere"
Earth and related Environmental sciences
short wave flux
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In principle, when the angular distribution of the energy is known it is possible to estimate instantaneous flux at the Top Of the Atmosphere (TOA) in any viewing geometry. Nevertheless due to the coarse angular bins resolution used to define Angular Distribution Models (ADMs) clear sky TOA Short Wave (SW) flux retrievals are unreliable for footprints near the specular reflection direction. Consequently, radiance-to-flux conversion is generally not performed in the sun glint regions. However, ignoring these samples (e.g.; by not providing a TOA flux estimate) can introduce biases in regional mean fluxes because fluxes over cloudy portions of a region will contribute disproportionately to the overall regional mean. By combining the high temporal sampling of the sun glint regions afforded by geostationary orbit with information contained in clear ocean SW ADMs we show that an improved estimation of the reflected SW flux at TOA is possible. Moreover, along the coastlines of continents, scenes which are a mix of two or more types (e.g.; ocean and land, land and desert) occur. Since data used to build ADMs were generally not sorted for mixed-scene type, instantaneous SW TOA flux is determined using the ADM that corresponds to the surface type with the highest percent coverage over the footprint when a footprint contains a mixture of surface types. As an example, near coastlines, if most of the footprint point spread function-weighted area is over ocean, an ocean ADM is used to convert the radiance to flux. In converse, if most of the footprint area is over land, one of the land ADMs is used. However, due to the large anisotropy difference which exists between ocean and land ADMs this leads to generate large discontinuities in the retrieved fluxes over coastlines regions. Strategy is given here to correct such a bias in the reflected SW flux estimation at the TOA.
CitationBertrand, C.; Clerbaux N.; Ipe A.; Dewitte S.; Gonzalez L. (2004). "Regional biases in the retrieved instantaneous reflected short wave flux at the top of the atmosphere". , Issue Proceedings of the 2004 EUMETSAT Meteorological Satellite Conference, Prague, Czech Republic, 31 May - 4 June 2004, pp. 533-540, IRM,