Integration of Cygnss Wind and Wave Observations with the Wavewatch III Numerical Model

The Cyclone Global Navigation Satellite System (CYGNSS) mission employs measurements of the quasi-specular forward scattering cross section of the ocean surface for retrieving sea surface wind speed and roughness globally and, particularly, in the inner core of tropical cyclones. CYGNSS Level 2 data products include the ocean surface wind speed U10 and the mean square slope (MSS). An "excess MSS" approach has been previously proposed to account for sea state condition effects, including the presence of non-local swell and the degree of wave development, to reduce the influence of these effects and thereby improve wind speed retrievals. The approach requires ancillary information on the sea surface MSS and wind speed from models, and has been shown to provide some improvement in wind speed retrievals. In this work, the inclusion of an additional parameter, the inverse wave age, is examined to determine if additional improvements can be achieved. MSS and inverse wave age information is obtained from the WaveWatch III model run by IFREMER, and is used to compute a feedback signal for a closed-loop retrieval algorithm for both wind speed and MSS. The goal of the effort is to improve further the accuracy of CYGNSS Level 2 wind speed retrievals, and also to provide additional wave information if possible. This paper also investigates the technical methodology and potential benefits of integrating CYGNSS observations into the WW3 model.