New Observations From the SWIM Radar On-Board CFOSAT: Instrument Validation and Ocean Wave Measurement Assessment
|Author(s)||Hauser Daniele1, Tourain Cedric2, Hermozo Laura2, Alraddawi D.1, Aouf L.3, Chapron Bertrand4, Dalphinet A.3, Delaye L.5, 6, Dalila M.7, Dormy E.8, Gouillon F.2, Gressani Victor9, Grouazel Antoine4, Guitton Gilles10, Husson R.7, Mironov Alexey11, Mouche Alexis4, Ollivier A.7, Oruba L.1, Piras E.7, Suquet R. Rodriguez2, Schippers P.5, Tison C.2, Tran Ngan7|
|Affiliation(s)||1 : Univ Paris Saclay, CNRS, Sorbonne Univ, LATMOS,UVSQ, F-78280 Guyancourt, France.
2 : Ctr Natl Etud Spatiales, F-31400 Toulouse, France.
3 : Meteo France, Div Marine & Oceanog, F-31100 Toulouse, France.
4 : Ifremer, Lab Oceanog Phys & Spatiale LOPS, F-29280 Plouzane, France.
5 : ACRI ST, F-78280 Guyancourt, France.
6 : Inst Natl Propriete Ind, F-92677 Courbevoie, France.
7 : Collecte Localisat Satellites, F-31520 Ramonville St Agne, France.
8 : Ecole Normale Super, F-75005 Paris, France.
9 : Ifremer, F-29280 Plouzane, France.
10 : Oceandatalab, F-29280 Locmaria Plouzane, France.
11 : Eodyn, F-29280 Plouzane, France.
|Source||Ieee Transactions On Geoscience And Remote Sensing (0196-2892) (Ieee-inst Electrical Electronics Engineers Inc), 2021-01 , Vol. 59 , N. 1 , P. 5-26|
|WOS© Times Cited||12|
|Keyword(s)||Spaceborne radar, Radar cross-sections, Surface waves, Sea surface, Instruments, Altimeter, ocean wave spectra, radar measurements, scatterometer, sea surface, spaceborne radar, speckle noise|
This article describes the first results obtained from the Surface Waves Investigation and Monitoring (SWIM) instrument carried by the China France Oceanography Satellite (CFOSAT), which was launched on October 29, 2018. SWIM is a Ku-band radar with a near-nadir scanning beam geometry. It was designed to measure the spectral properties of surface ocean waves. First, the good behavior of the instrument is illustrated. It is then shown that the nadir products (significant wave height, normalized radar cross section, and wind speed) exhibit an accuracy similar to standard altimeter missions, thanks to a new retracking algorithm, which compensates a lower sampling rate compared to standard altimetry missions. The off-nadir beam observations are analyzed in detail. The normalized radar cross section varies with incidence and wind speed as expected from previous studies presented in the literature. We illustrate that, in order to retrieve the wave spectra from the radar backscattering fluctuations, it is crucial to apply a speckle correction derived from the observations. Directional spectra of ocean waves and their mean parameters are then compared to wave model data at the global scale and to in situ data from a selection of case studies. The good efficiency of SWIM to provide the spectral properties of ocean waves in the wavelength range [70500 m] is illustrated. The main limitations are discussed, and the perspectives to improve the data quality are presented.