Impact of solar radiation on sea surface salinity remote sensing by spaceborne Synthetic Aperture Imaging Radiometers. - Université Pierre et Marie Curie Accéder directement au contenu
Communication Dans Un Congrès Année : 2004

Impact of solar radiation on sea surface salinity remote sensing by spaceborne Synthetic Aperture Imaging Radiometers.

Résumé

Since the sun is a very bright radiation source at L-band, reception of direct and earth-reflected solar radiations by downward-looking radiometers raises a significant challenge for the remote sensing of ocean surface salinity. For a given spaceborne mission concept, the impact of the sun radiations depends on the sensor antenna properties, the location of the sun relative to both the radiometer receiver and the reflecting surface, as well as on the surface scattering properties of the observed Earth scene. Effects on interferometric data, (i.e. visibilities), provided by Synthetic Aperture Imaging Radiometers (SAIR) need to be accounted for; the affected area, determined through both geometrical and geophysical considerations, will have to be either masked or flagged, or submitted to specific correction procedures, for correct sea surface salinity retrieval. Focusing on the future ESA Soil Moisture and Ocean Salinity (SMOS) space mission, we provide quantitative and qualitative estimates for measurements contamination by sun as expected for the mission period 2007-2010, and we derive methods that can serve to develop a consistent correction strategy. The sun brightness temperature expected at 1.4 GHz during the mission period is first estimated from past solar flux data. Numerical simulations of the predicted illumination geometry of SMOS antenna by the sun reveal that direct leakage by aliasing of the sun image will frequently occur during the sun seasonal cycle. Assuming that the earth surface is locally flat, we further show that specular reflections of sun radiations on the earth surface should never affect SMOS data in the alias-free instrument field of view. However, when applying an asymptotic model to predict the forward scattering of sun radiations from a more realistic rough sea surface, significant contamination by sunglitter effects might occur, with an intensity depending on the date and the local surface roughness conditions. A robust regularized reconstruction method providing a band-limited solution is used to retrieve brightness temperature maps (TB). Simulations are carried out considering in a first step an ideal instrument, then a more realistic one. In both cases, visibilities corresponding to the observed scene contaminated by the presence of the sun are simulated and then blurred by a radiometric noise. The contribution of sunglitter effects is subtracted and the regularized reconstruction process is applied.. A sensitivity study on the impact of a bias added to the simulated TB of the sunglitter effects is also carried out.
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Dates et versions

hal-00005166 , version 1 (06-06-2005)

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Eric Anterrieu, Bruno Picard, Philippe Waldteufel, Nicolas Reul. Impact of solar radiation on sea surface salinity remote sensing by spaceborne Synthetic Aperture Imaging Radiometers.. Geoscience and Remote Sensing Symposium, 2004. IGARSS '04. Proceedings. 2004 IEEE International , Sep 2004, Anchorage Alaska, United States. pp.1926-1929, ⟨10.1109/IGARSS.2004.1370719⟩. ⟨hal-00005166⟩
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