Up-to-downwave asymmetry of the CFOSAT SWIM fluctuation spectrum for wave direction ambiguity removal

Huimin Li (1) , Danièle Hauser (2) , Bertrand Chapron (3) , Frédéric Nouguier (3) , Patricia Schippers (4) , Biao Zhang (1) , Jingsong Yang (5) , Yijun He (1)

1 NUIST - Nanjing University of Information Science and Technology
2 SPACE - LATMOS
3 LOPS - Laboratoire d'Océanographie Physique et Spatiale
4 ACRI-ST - Analytic and Computational Research, Inc. - Earth Sciences
5 SOED - State Key Laboratory of Satellite Ocean Environment Dynamics

The surface waves investigation and monitoring (SWIM) aboard the China-France Oceanography Satellite 2 (CFOSAT), a pioneer conically scanning wave spectrometer, was successfully launched on October 29, 2018. Its innovative configuration composed of one nadir and 5 rotating near-nadir beams is designed to simultaneously observe the significant wave height as well as the directional wave spectrum at global scale. In this study, we examine the two-dimensional fluctuation spectrum of the three spectral beams (θ = 6 °,8 ° ,10 °) by combining all the azimuth directions within one entire rotation of 360 °. Spectral analysis of the radar backscattering profile along each azimuth is systematically carried out using the periodogram technique. The obtained fluctuation spectrum is consistent with the collocated wave slope spectra in terms of the qualitative wave features. Moreover, a quantitative up-to-downwave asymmetry of the fluctuation spectrum is documented with larger spectral level in the upwave direction for all the three spectral beams. Magnitude of the defined up-to-downwave spectral ratio are mostly greater than 1 with the down-to-upwave ratio smaller than 1. This asymmetry characteristics can be readily utilized to remove the 180° wave direction ambiguity from a practical point of view. The preliminary results demonstrate that the 10° beam shows better performance in comparison to the other two beams. This shall lay strong basis for the operational implementation of such algorithm to resolve the direction ambiguity.

Mots clés: CFOSAT Satellite; SWIM Instrument; Ocean Surface Waves; Backscattering

Domaines: Océan, Atmosphère

Huimin Li, Danièle Hauser, Bertrand Chapron, Frédéric Nouguier, Patricia Schippers, et al.. Up-to-downwave asymmetry of the CFOSAT SWIM fluctuation spectrum for wave direction ambiguity removal. IEEE Transactions on Geoscience and Remote Sensing, 2022, 60, pp.5103012. ⟨10.1109/TGRS.2021.3086483⟩. ⟨hal-03084669v2⟩