Swim now in orbit: a new horizon for wave observation

Abstract : The CFOSAT (China France Oceanography SATellite) mission is a CNES-CNSA space mission for ocean surface wind and wave observation. The satellite has been successfully launched on October, 29th, 2018 from China. The satellite behaves perfectly well until now with nice scientific acquisitions. For the very first time, wind and waves are observed at the same time and place. These simultaneous observations open new research fields on climate monitoring, sea-air interactions understanding and sea state forecasting. CFOSAT embarks two payloads: a wave scatterometer, SWIM (French contribution) and a wind scatterometer, SCAT (Chinese contribution). Both are Ku-band real aperture radar taking advantage of different backscattering properties. At high incidence angles (SCAT), the radar signal is sensitive to Bragg scattering, i.e. small surface roughness induced by the wind. At low incidence angles (SWIM), the radar backscattering depends only on large slopes, i.e. the waves. In this paper, we will present the status on the SWIM instrument and the SWIM products produced by the French ground segment. This status will be provided after 7 months in orbit, at the end of the commissioning phase. At the time of the writing of the abstract (few days after the launch), we are just checking the health of the satellite and the instruments as well as the generation of the first products. We are not thus able to provide quantitative results to the reviewers at this stage. During the commissioning phase, the internal calibration modes of SWIM are tested (internal impulse response, antenna calibration law, reception noise level). The different acquisition modes are also tested (sequence of the six beams and on-board processing options). The CFOSAT system is composed of the satellite with SWIM and SCAT on-board and two ground segments, one in China (CHOGS) and one in France (FROGS). Both mission centers process all the SWIM and the SCAT data. This paper is relative to the processing performed at FROGS for SWIM only. The CFOSAT data are processed in near real time in the French mission center up to level 2 (CNES) and in differed time from level 2 to level 4 (IFREMER). The products are available on-line on the AVISO+ website. The main scientific products of SWIM are the 2D wave spectrum at a spatial scale of 70x90 km², the backscattering coefficient profiles per 0.5° step in incidence and 15° step in azimuth and the significant wave height and wind speed from the nadir beam. The paper will detail the performance of the instrument relative to SNR and backscattering coefficient accuracy, pointing knowledge accuracy. The overall availability of the data will also be discussed (coverage over ocean, distance to coasts, coverage of the continents and ice sheets). We will also present the results on level 2 products.
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Submitted on : Wednesday, October 23, 2019 - 11:02:49 AM
Last modification on : Friday, January 10, 2020 - 3:42:35 PM

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  • HAL Id : insu-02328399, version 1

Citation

Céline Tison, T. Amiot, Cedric Tourain, Danièle Hauser, L. Rey, et al.. Swim now in orbit: a new horizon for wave observation. Living Planet Symposium, May 2019, Milan, Italy. ⟨insu-02328399⟩

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