Ring-waves generated by water drops impacting on water surfaces at rest

Radar observations of the ocean surface can be affected by impacting raindrops. Ring-wave measurements are presented for drops of 2.2 and 2.8 mm in diameter impacting on fresh and salt water surfaces initially at rest. They are based on the observation of the mirror image of a sharp edge on the perturbed surface. The retrieved wave profiles show a rather stable characteristic wavenumber (0.2 mm/sup -1/) and very small wave amplitudes: the fraction of the incident kinetic energy converted into ring-waves is of the order of 1%.