CFOSAT Mission: Using of Swim Measurements for Improving Scat Wind Vector Retrieval

CFOSAT (the China France Oceanography Satellite) is the joint mission from the Chinese and French Space Agencies to jointly perform global ocean surface wind and sea state observation and monitoring. The satellite will carry two Ku-band radars: the wave scatterometer (SWIM) and the wind scatterometer (SCAT). Such a unique configuration provides multi-look and multi-angle observations to reconstruct key parameters of local sea surface conditions: the directional wave spectrum and the determination of the sea surface wind speed and direction. From unique collocated wave and wind measurements, each single instrument observation by its own can benefit from the other one. As often discussed, radar returns, at the same location but for different angles of observations, will possibly exhibit different sensitivity with regard to various sea surface parameters, i.e. near-surface wind speed and direction, significant wave height, sea state degree of development and/or local swell wave spectrum characteristics. This often results in radar signal dispersion which limits the precision of the retrieval algorithms from radar remote sensing measurements. Accordingly, the potential to benefit from additional information from a co-located second instrument could be strongly useful in the correction of such factors. The present work considers the possibility of using the near-nadir SWIM measurements to improve the wind estimates from the scatterometer inversion algorithm. Preliminary estimates and simulations confirm that some types of errors, e.g. due to SCAT antenna geometry and configuration, can largely be reduced. As well, additional improvement can be expected for the measurements under low-wind and rapidly changing sea conditions.