Modeling of Sea State Conditions for Improvement of Cygnss L2 Wind Speed Retrievals

摘要

The Level 2 data product of the Cyclone Global Navigation Satellite System (CYGNSS) mission includes the retrieved ocean surface wind speed and the mean square slope (MSS), which are derived from the Level 1 normalized bistatic radar cross section (NBRCS). In the current L2 retrieval algorithm, the wind speed is retrieved using empirical geophysical model functions (GMFs) based on matchups with ground truth wind speed. However, sea state conditions, including the presence of external swell and the degree of wave development, complicate the ocean surface wave spectra and increase the uncertainty of the wind speed retrieval. An excess MSS approach is proposed to model sea state conditions. It calculates the excess MSS responsible for the sea state condition effects using ancillary data and the Elfouhaily et al. wave spectral model. A case study demonstrates that this approach reduces the wave effect (due to the sea state condition) on the CYGNSS NBRCS and improves the L2 wind speed retrieval.