A new Geophysical Model Function for estimating whitecap coverage from Ku-band scatterometers

Satellite-based scatterometers like QuikSCAT are used to measure wind velocities over the ocean, but the surface backscatter signal used to identify the wind velocity includes backscatter from whitecaps. The contributions of whitecaps to the scatterometer backscatter signal are not distinguished in Geophysical Model Functions (GMF) used to determine the 10-meter equivalent neutral wind (U10EN) from QuikSCAT and RapidScat. Recent efforts in determining the whitecap fraction using historically published parameterizations and U10EN from QuikSCAT have met with mixed results. I present the results from a preliminary GMF for estimating the surface whitecap fraction using QuikSCAT L1B σ⁰ data and compare our success to U10EN-based parameterizations.

Visible, infrared, and passive microwave sensors often require quantifying and extracting the whitecap contributions before studying other phenomena. This extracted signal can be used to determine the surface whitecap fraction. The active and total whitecap fractions have been successfully extracted from WindSat, a passive microwave radiometer, at 10 GHz and 37 GHz to develop the WindSat Whitecap Database (WWD) for 2006. The WWD whitecap fraction data is collocated in space and time with the QuikSCAT L1B and wind speed observations, and the GMF is developed using these data. Important contributing parameters such as SST and latitude are discussed. The long-term goal of this GMF is to provide whitecap estimates for the entire QuikSCAT mission and for future Ku-band scatterometers such as RapidScat.