Scatterometric signatures of multivariate drop impacts on fresh and salt water surfaces

Microwave signatures of the ocean surface are affected by wind and rain. To support the development of theoretical models for remote sensing applications, radar scatterometry experiments at 13.5 and 36GHz with VV polarization were conducted at the Rain-Sea Interaction Facility at NASA Wallops. Backscatterings from rain drop impacts on fresh and salt water surfaces were measured with an incidence angle of 30 for eight different drop sizes. Results are also presented for terminal and non-terminal fall velocities. Surface features were imaged by an ultrahigh-speed digitalcamera synchronized with radar data acquisition and their geometrical characteristics were determined. Backscattered powers from crowns, craters, stalks and ring-waves were measured and compared. These measurements confirm that for slant radar configurations, ring-waves are the dominant scattering contribution, even though stalk scattering is not negligible.