Limb-darkening Models from Along-Track Operation of the ERBE Scanning Radiometer

G. Louis Smith Atmospheric Sciences Division, NASA/Langley Research Center, Hampton, Virginia

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Natividad Manalo-Smith Lockheed Engineering and Sciences Co., Hampton, Virginia

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Lee M. Avis Atmospheric Sciences Division, NASA/Langley Research Center, Hampton, Virginia

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Abstract

During January and August 1985, the scanning radiometers of the Earth Radiation Budget Experiment (F-RBE) aboard the Earth Radiation Budget Satellite (ERBS) and the NOAA-9 satellite were operated in along- track scanning modes. Along-track scanning permits the study of many measurement problems. It provides the data for developing a limb-darkening model for a single site over a short period of time and also permits the identification of the scene from data taken at small nadir angles. The earth-emitted radiation measured by the scanners has been analyzed to produce limb-darkening models for a variety of scene types. Limb-darkening models relate the radiance in any given direction to the radiant flux. The scene types were computed using measurements within 1O° of zenith. The models have values near zenith of 1.02–1.09. The typical zenith values of the model are 1.06 for both day and night for FRBS, and for NOAA-9, 1.06 for day and 1.05 for night. Mean models are formed for the ERBS and NOAA-9 results and are found to differ less than 1%, the ERBS results being the higher. The models vary about 1% with latitude near zenith and agree with earlier models that were used to analyze ERBE data typically to 2%.

Abstract

During January and August 1985, the scanning radiometers of the Earth Radiation Budget Experiment (F-RBE) aboard the Earth Radiation Budget Satellite (ERBS) and the NOAA-9 satellite were operated in along- track scanning modes. Along-track scanning permits the study of many measurement problems. It provides the data for developing a limb-darkening model for a single site over a short period of time and also permits the identification of the scene from data taken at small nadir angles. The earth-emitted radiation measured by the scanners has been analyzed to produce limb-darkening models for a variety of scene types. Limb-darkening models relate the radiance in any given direction to the radiant flux. The scene types were computed using measurements within 1O° of zenith. The models have values near zenith of 1.02–1.09. The typical zenith values of the model are 1.06 for both day and night for FRBS, and for NOAA-9, 1.06 for day and 1.05 for night. Mean models are formed for the ERBS and NOAA-9 results and are found to differ less than 1%, the ERBS results being the higher. The models vary about 1% with latitude near zenith and agree with earlier models that were used to analyze ERBE data typically to 2%.

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