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Level 2 Products from the 2021 campaign of the airborne Ku-Band KuROS radar

Résumé
This data set contains directional spectra of surface ocean waves obtained from radar observations over the ocean surface with the airborne Ku-Band radar named "KuROS".
This data set is relative to the Level 2 product, which contains the density spectrum of wave slopes (directional spectrum) or wave heights (omni-directional spectrum) for ocean waves between about 30 m and 300m in wavelength and for all directions of propagation between 0° and 360° (referred to the true North). Each spectrum corresponds to a 30s- data acquisition, which represents approximately a 3 km distance along the airplane track. Each directional spectrum is provided with a 15° resolution in azimuth and with a 180° ambiguity on the propagation direction of the waves.
This data set is relative to the 2021 SUMOS campaign with 17 flights over the gulf of Biscaye, among which 13 were coordinated with CFOSAT passages.

Méthode(s)
The wave spectra are obtained in each azimuth direction from a spectral analysis of the relative modulations of the normalized radar cross-sections in the elevation direction ( footprint of about 800 m) and by assuming a linear relationship between the long wave slopes and the normalized radar cross-section modulations (see Jackson et al, J. Geophys. Res. 1985). The effect of speckle is minimized by using a cross-spectrum analysis between two samples separated by 66ms. Details of the processing are given in Caudal et al, JAOT 2014.

Informations techniques
The files provide two-dimensional spectra as wave slope spectra (symmetrized from estimations opposite directions at ±180°), omni-directional spectra expressed as wave height spectra, integral parameters of the spectra (wave height, peak direction, peak wavenumber), and a “modulation transfer function” coefficient estimated from the KuROS normalized radar cross-section to convert signal modulation spectra into wave spectra. A filtering of parasitic energy at low wave number has been applied using an empirical model (fitted to a Lorentzian function) and imposing zero energy in the first two wavenumber bins.