Optimizing an observable for ocean wind speed retrieval from calibrated GNSS-R delay-Doppler maps

The fundamental measurement produced by Global Navigation Satellite System Reflectometry (GNSS-R) is the cross-correlation between the scattered signal and a local copy of the GNSS code and carrier, producing a bivariate function defined as the delay-Doppler map (DDM). The shape of the DDM is sensitive to the roughness of the scattering surface and, through various empirical models, the ocean surface winds. Ocean winds can be retrieved by fitting a scattering model to DDM observations, or identifying an observable, such as trailing edge slope or DDM area exceeding a threshold. A variety of such methods have been demonstrated with airborne experiments. With the selection of the CYGNSS mission by NASA, there is now a need to extend these methods to spaceborne measurements.