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Estimation par satellite de l'humidité spécifique au dessus de l'océan par radiométrie hyperfréquence

Abstract : Ocean plays a very important role in the regulation of earth climate through heat exchange with atmosphere, which are done for most part in the form of latent heat flux (LHF). LHF depends on specific humidity some meters over the ocean surface. This variable isn't well controlled in meteorological models and too few observations are available on global scale for calculating humidity fields and LHF, although necessary to force oceanic circulation models for example. In this work, we analyse potential of remote sensing data to estimate near surface humidity. Major interest of satellite is they enable observations of the whole ocean at temporal scale of some days only. In order to estimate specific humidity, we use brightness temperatures data measured by microwave radiometers AMSU-A (Advanced Microwave Sounding Unit-A) and AMSU-B on board NOAA 15, 16 and 17 satellites. AMSU-A has 15 channels between 23.8 GHz and 89 GHz, with a spatial resolution approximately of 48 Km, and AMSU-B has 5 channels between 89 GHz and 183.31 GHz, with a spatial resolution of 16 Km. We use AMSU radiometer because they have important number of channels (20 channels), whose some are sensitive to water vapour. Despite their interesting potential, AMSU radiometers have not yet been used for the retrieval of surface specific humidity. Two methods are presented: multiple linear regression and artificial neural networks. Using neural networks approach, we improve specific humidity retrieval of 21.8% in comparison to reference algorithm (Bentamy et al., 2003). This is equivalent to a rms error of 0.86g/kg in comparison to buoys (TAO and PIRATA) data used for validation. All the results found in this study show clearly that satellite supply a complementary point of view in comparison to operational models, and observations, in relation to surface humidity.
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  • HAL Id : tel-00737712, version 1

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Abdou Aziz Mbengue. Estimation par satellite de l'humidité spécifique au dessus de l'océan par radiométrie hyperfréquence. Océanographie. Université de Versailles-Saint Quentin en Yvelines, 2009. Français. ⟨NNT : 2009VERS0044⟩. ⟨tel-00737712⟩

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