Optical and radar observations of steep and breaking waves of decimeter range („mesowaves”) on the sea surface: electrodynamical and hydrophysical interpretation

Optical and radar (ground based, aircraft-, ship- and satellite-borne) observational data are analyzed, evidencing important role of steep and breaking waves of decimeter range („mesowaves” or “micro-breaking”) in forming radar image of the sea surface. First of all, mesowaves are clearly seen on numerous photos, made in different areas of the World Ocean, in particular, on images, obtained by Institute of Oceanology of Polish Acad.Sci. Optical data include also photos of higher resolution, made from aircraft. At second, mesowaves manifest themselves on radar sea images at low grazing angles in the form of bright spots, as a rule, with abnormal polarization ratio. Radar images were systematically studied by ground-based two polarization mobile radar of Space Research Institute, Russ. Acad. Sci. on the Black Sea, Gelendzik, in 1999-2005. Episodic observations of this kind were performed also by ship radar Kelvin Hughes, installed on the training ship “Navigator XXI” of the Szczecin Maritime University.
Steep mesowaves may serve also as important factor for internal oceanic waves visualization on SAR images. All the observations mentioned might be explained in frame of the “four-five channels” electrodynamical model, developed by SRI RAS. Unlike Bragg theory, this model presents the signal, backscattered from individual sharp-crested mesowaves as discrete sum of waves, multiply reflected and diffracted by mesowaves crests and their footnotes. Such a discrete model satisfactorily describes observed polarization, angular and frequency characteristics of radar echo-signals. In particular, this model describes significant, up to 1 m2, radar cross-section of the individual sharp-crested mesowaves of 1 m length: so named “super-events”, which may simulate real small-size objects on the sea surface. Mechanisms for sharp-peaked mesowaves generation are still not clear until now. One can not exclude serious role of spilling processes caused with wind-water interaction. One more problem for discussion are criteria for distinguishing between micro-breaking (decimeter scale mesowaves) and macro-breaking (large scale breaking gravity waves) processes on the sea radar images.