Cross-polarization geophysical model function for marine wind speed retrieval: Laboratory modeling and examples of hurricane wind speed retrieval from satellite imagery

Laboratory experiments directed to investigation of dependencies of the X-band normalized co-polarized and de-polarized radar cross-section on wind speed (U₁₀) and incident angle (θ) are presented. Parameters of air-flow velocity and surface wind waves were measured simultaneously. It was shown that both co-polarized and depolarized radar return depend on incidence angle; the depolarized return is less sensitive. Analysis of the Doppler spectra of the radar backscatter enabled us to conclude that the radar return is formed by resonant scatters moving with the velocity exceeding in 20% the phase velocity of the energy containing surface waves. Basing on the measurements the X-band and C-band geophysical model functions (GMF) were derived for U₁₀ =10-40 m/s and θ=30°-60°. Examples of hurricane wind speed retrieval with the use of the new GMF are discussed.