Laboratory measurements of microwave emission from capillary waves

The results of polarimetric microwave measurements of thermal emission from a water surface with artificial periodic structure are presented. The goal of the experiment was a verification of the model describing the polarized microwave emission from gravity-capillary waves on a sea surface. The structure in a water tank was produced by a set of parallel nylon threads raised a little over a surface. Due to surface tension, the water surface takes a periodic profile. The measurements of the three Stokes parameters of the emission were carried out with a Ka-band polarimeter. The experimental setup allowed measurements over a wide range of view angles (from near-nadir to 70 degrees). The tank rotation allowed varying the azimuthal angle between the periodic structure and the observation plane over 300 degrees. The experimental data show the existence of the resonant peak in the Stokes parameters predicted by the model. The amplitude of the peak reached 10 kelvin. Also, drastic contrasts were registered in the azimuth dependencies of the Stokes parameters. This result is evidence of the important role that the short gravity-capillary waves play in the sea-surface polarized microwave emission.