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Theses

De la détermination de la salinité de surface des océans à partir de mesures radiométriques hyperfréquences en bande L

Abstract : The remote sensing by satellite is nowadays a component with whole share of oceanography. It makes it possible to take measurements of winds, of Sea Surface Temperature (SST), of water color, of topography... with spatial and temporal covers quite higher than those obtained by in situ methods. However, there does not exist at the present time satellite measurement of Sea Surface Salinity (SSS) and this one remains under sampled at the same time spatially and temporally. Salinity being a significant parameter for the circulation of the oceanic water masses, its global and regular observation would constitute a substantial contribution to physical oceanography. This is why many scientific teams throughout the world currently take up the technological challenge of the remote sensing of the SSS by satellite, and particularly in Europe thanks to the mission of the European Space Agency "Soil Moisture and Ocean Salinity" (SMOS). During my thesis, I studied the feasibility of the measurement of the SSS with a microwave radiometer at L-band (i.e. frequency = 1.4 GHz < = > wavelength = 21 cm), by estimating the uncertainty sources on the SSS which will be restored within the framework of the SMOS mission. For that, I coded a direct model, which simulates the physical processes intervening from oceanic surface up to the antenna of the radiometer. This model is made up of a "two scales" emissivity model (i.e. one distinguishes the waves being “large" or "small" with respect to the wavelength of the radiometer) of the sea surface, and of a radiative transfer model for the atmosphere. The emissivity model allowed me to estimate the sensitivity of the ocean brightness temperature (Tb) to the geophysical oceanic parameters (i.e. SSS, SST, and roughness of the surface induced by the wind or the by swell), like the uncertainty on this sensitivity by comparing the results obtained starting from different parameterizations. I concluded from these studies that the sensitivity of Tb to the SSS is relatively well-known (of the order of some tenths of a Kelvin by psu) but that the effect of roughness is very uncertain because of the imprecision of the wave spectrum models, whereas this effect does not seem to be negligible (sensitivity of Tb to the wind lying between 0.12 to 0.25 K/(m/s) according to the wave spectrum model). The model of radiative transfer allowed me to estimate various contributions of the atmosphere (attenuation of the radiations and self-emission), as well as the sensitivity of these contributions to atmospheric parameters (i.e. profiles of temperature, pressure and relative humidity). At L-band, the atmosphere is almost transparent (optical thickness ~ 0.01 neper) and its Tb is of the order of 2 K. These effects are not very sensitive to atmospheric parameters, particularly with the water vapor. I also present in the thesis comparisons between the model and recent radiometric measurements at L-band (WISE 2000, WISE 2001 and EuroSTARRS campaigns) as well as the conclusions on the validity of the various models of wave spectrum studied.
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https://tel.archives-ouvertes.fr/tel-00003277
Contributor : Emmanuel Dinnat <>
Submitted on : Wednesday, August 27, 2003 - 5:46:00 PM
Last modification on : Thursday, December 10, 2020 - 10:52:43 AM
Long-term archiving on: : Friday, April 2, 2010 - 6:38:14 PM

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  • HAL Id : tel-00003277, version 1

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Emmanuel P. Dinnat. De la détermination de la salinité de surface des océans à partir de mesures radiométriques hyperfréquences en bande L. Physique [physics]. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00003277⟩

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