Observation of high-resolution fetch-limited wave growth using CFOSAT near-nadir measurements

CFOSAT is the joint space mission of the French (CNES) and Chinese (CNSA) space agencies dedicated to the observation of ocean surface wind and waves. Two main on-board payloads, the Ku-band near-nadir wave scatterometer SWIM and dual-polarization Ku-band wind scatterometer SCAT for the first time provide regular synchronized surface wind vector and sea state observations on a global scale. 
 
After the first year of the mission, SWIM innovative wave scatterometer conception proved to be suitable for space-born directional wave spectra measurements. The overall performance of the instrument and the quality of inverted data are close to the planned specifications. Moreover, in particular cases, precise wave parameters can be estimated even in limited coastal seas with varying wave and wind conditions.
 
In this work, we will show examples of high-resolution directional wave spectrum fetch evolution as observed by CFOSAT mission. The present analysis was performed for areas with fetch-determined conditions, during periods when waves were generated by strong coastal winds. The dataset includes spectra starting from young wind waves (~20 km fetch distance) to mature almost developed sea state (>450 km fetch). The unique multi-beam configuration of SWIM provides multiple estimates of wave spectral parameters all over the sensor footprint along the satellite track. This allows the capturing of the very fine details of spectral variability with distance from the coast. It will be shown, the observed deviation of direction and wavelength of the measured spectral peak from a wave growth fetch law can be attributed to time-varying or topography-induced coastal wind field inhomogeneities. In some cases, this can be explained by local surface current configuration. The obtained results can be directly compared with third party remote sensing observations, numerical model outputs, classical wave fetch-growth laws, and existing empirical parametrizations.