Up-to-Downwave Asymmetry of the CFOSAT SWIM Fluctuation Spectrum for Wave Direction Ambiguity Removal

Type Article
Date 2022
Language English
Author(s) Li HuiminORCID1, 2, Hauser DanieleORCID3, Chapron Bertrand4, Nouguier FredericORCID4, Schippers Patricia5, Zhang BiaoORCID1, Yang JingsongORCID2, He YijunORCID1
Affiliation(s) 1 : School of Marine Sciences, Nanjing University of Information Science and Technology, Nanjing, China
2 : State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China
3 : Laboratoire Atmosphére, Observations Spatiales (LATMOS), UVSQ, Centre National de la Recherche Scientifique (CNRS), Université Paris-Saclay, Sorbonne Université, Guyancourt, France
4 : IFREMER, Univ. Brest, CNRS, IRD, Laboratoire d’Oceanographie Physique et Spatiale (LOPS), Plouzané, France
5 : ACRI-ST, Guyancourt, France
Source Ieee Transactions On Geoscience And Remote Sensing (0196-2892) (Institute of Electrical and Electronics Engineers (IEEE)), 2022 , Vol. 60 , N. 5103012 , P. 1-12
DOI 10.1109/TGRS.2021.3086483
WOS© Times Cited 3
Keyword(s) Azimuth, Modulation, Spaceborne radar, Backscatter, Sea measurements, Sea surface, Radar measurements, China-France Oceanography Satellite (CFOSAT) surface wave investigation and monitoring (SWIM), up-to-downwave asymmetry of fluctuation spectrum, wave direction ambiguity removal

The surface wave investigation and monitoring (SWIM) aboard the China-France Oceanography Satellite (CFOSAT), a pioneer conically scanning wave spectrometer, was successfully launched on October 29, 2018. Its innovative configuration composed of one nadir and five rotating near-nadir beams is designed to simultaneously observe the directional wave spectrum at a global scale. In this study, we systematically implement the spectral analysis of the radar backscattering with the periodogram technique to obtain the fluctuation spectrum for each azimuth direction. The 2-D fluctuation spectrum of the three spectral beams ( θ=6∘ , 8°, and 10°) combines all the azimuth directions within one entire rotation of 360°. The case study demonstrates that the wave features (peak wavelength and direction) are roughly consistent between the estimated fluctuation spectrum and the collocated WaveWatch III wave slope spectrum. A marked up-to-downwave asymmetry of the fluctuation spectrum with larger spectral level in the upwave direction for all the three spectral beams is observed. A ratio is defined between the fluctuation spectrum within the [0°, 180°] sector relative to the [180°, 360°] sector. Statistics display that this ratio is greater than 1 when it denotes the up-to-downwave ratio and smaller than 1 for the down-to-upwave ratio. This observed spectrum asymmetry is linked to the asymmetric modulation from upwind to downwind. In addition, we employ such finding to help remove the 180° wave direction ambiguity from a practical point of view. Preliminary results of the direction ambiguity removal display a bias of 41.3°, 40.6°, and 36.7° for the beams. The 10° beam shows slightly better performance compared to the other two beams in terms of bias and standard deviation. This shall lay a strong basis for the operational implementation of such algorithm to resolve the direction ambiguity.

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Li Huimin, Hauser Daniele, Chapron Bertrand, Nouguier Frederic, Schippers Patricia, Zhang Biao, Yang Jingsong, He Yijun (2022). Up-to-Downwave Asymmetry of the CFOSAT SWIM Fluctuation Spectrum for Wave Direction Ambiguity Removal. Ieee Transactions On Geoscience And Remote Sensing, 60(5103012), 1-12. Publisher's official version : https://doi.org/10.1109/TGRS.2021.3086483 , Open Access version : https://archimer.ifremer.fr/doc/00752/86383/