The Eddy Experiment: GNSS-R speculometry for directional sea-roughness   retrieval from low altitude aircraft
  We report on the retrieval of directional sea surface roughness, in terms of its full directional mean square slope (including direction and isotropy), from Global Navigation Satellite System Reflections (GNSS-R) Delay-Doppler-Map (DDM) data collected during an experimental flight at 1 km altitude. This study emphasizes the utilization of the entire DDM to more precisely infer ocean roughness directional parameters. In particular, we argue that the DDM exhibits the impact of both roughness and scatterer velocity. Obtained estimates are analyzed and compared to co-located Jason-1 measurements, ECMWF numerical weather model outputs and optical data. 
O. Germain, G. Ruffini, F. Soulat, M. Caparrini, B. Chapron and P.   Silvestrin