Laboratory polarimetric 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 is to verify the results of a model describing polarized microwave emission from gravity‐capillary waves on a sea surface. Periodic undulations of water surface were produced in a tank by a set of parallel nylon threads raised slightly above the mean surface. Due to surface tension, the water surface assumes a periodic profile; the amplitude of the roughness was changed by moving the frame with the threads up and down. The measurements of the three Stokes parameters of the emission were carried out with the Ka‐band polarimeter. The experimental setup allowed measurements to be made over a wide range of view angles (from near‐nadir to 70°). The tank rotation allowed variation of the azimuthal angle between the periodic structure and the observation plane of more than 300°. 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 K. Also, drastic contrasts were registered in the azimuth dependencies of the Stokes parameters. This result is evidence of the important role that short gravity‐capillary waves play in sea‐surface polarized microwave emission.