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Surface wind speed estimation over open ocean using bidirectional observation by Sentinel-2/MSI and Landsat-8/OLI
Author(s): Bertrand Fougnie; Olivier Hagolle; Sophie Lachérade
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Paper Abstract

Large stripes, observed on first Sentinel-2/MSI images over ocean, are not due to instrumental artifacts but to the target itself. The same kind of signature can be observed on Landsat-8/OLI. Both MSI and OLI instruments are known for their excellent radiometric quality for land observation. The MSI’s focal plane is composed by 12 elements to cover the 300km-swath, respectively 14 elements for a 185km-swath for OLI. For technical reason, elements were slightly shifted forward/backward alternatively in the focal plane. As a consequence, each element has a different viewing angle than the next/previous one, leading for a considered target on the ground to a significant difference in zenith/azimuthal viewing angles. These angular variations, fully acceptable for the land mission, become sensitive for specific targets such as sunglint, a highly directional signal. It was already demonstrated the possibility to retrieve surface wind speed from bidirectional space measurements with POLDER/PARASOL instruments. Indeed, using multiple viewing angles is a good way to better constrain the inversion because it doesn’t fully rely on the absolute estimation of a unique measurement. Somehow, MSI or OLI can be seen as bidirectional sensors for targets located between 2 elements of the focal plane. Knowing the exact acquisition geometry, the observed radiometric gap can be directly related to the surface wind speed. Because it is a relative estimation, this inversion becomes more robust to aerosol contamination. Finally, an improved retrieval can be foreseen thanks to the multiple spectral bands provided by MSI and OLI.

Paper Details

Date Published: 19 September 2016
PDF: 8 pages
Proc. SPIE 9972, Earth Observing Systems XXI, 997211 (19 September 2016); doi: 10.1117/12.2237597
Show Author Affiliations
Bertrand Fougnie, Ctr. National d'Études Spatiales (France)
Olivier Hagolle, CESBIO (France)
Sophie Lachérade, Ctr. National d'Études Spatiales (France)

Published in SPIE Proceedings Vol. 9972:
Earth Observing Systems XXI
James J. Butler; Xiaoxiong (Jack) Xiong; Xingfa Gu, Editor(s)

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