Optical And Microwave Sensing Of Breaking Waves In Ocean

Combined opt ical-microwave methods are applied for the study of ocean surface dynamics. wave breaking and foam formation. The main problem is the estimation of the ocean surface state from aerospace data. Several years ago we made a series of detailed laboratory experiments with the help of microwave radiometers of mm-, cmand dm-range combined with natural measurements as well as the creation of electrodynamic models of the effects observed. Alongside aircraft optical remote sensing of ocean surface under conditions close to wind speed change was applied. Ocean surface optical images with foam and whitecaps structures were processed by special computer metric algorithms. The focus of the studies was on foam formations as the most common type of two-phase medium in ocean. Laboratory experiments demonstrated radiation spectral and polarization characteristics dependence on foam layer dispersion structure. The effects of high absorption on foam bubbles play the crucial. role, and that accounts for their high emissivity. Experimental data well agree with the quasistatic model. in which effective dielectric permittivity depends on bubbles parameters and size distribution. Microwave properties of spray or concentrated droplet clouds found above foam coverage were investigated on the basis of numerical solution of radiation transfer equation for discrete scattering media. It was shown, in particular, that effects connected with the spray layer influence can yield both positive and negative brightness temperature contrasts, radiation spectrum depending on spray concentration. Undersurface bubble population influence on the ocean microwave radiation is observed mainly in long cmand dmranges. which is connected with the sharp change in skin depth characteristics because of its two-phase structure. Separate microwave investigation of different two-phase structures made it possible to design a complex microwave model of a general two-phase layer spray, foam, and bubble population combined. It is a multiparameter model that takes into account not o n l v the structure hierarchy of a real two-phase medium in the ocean, but also statictics and spatial distribution of wave breaking. We have found, for example. that size histograms and fractal dimensions differ for foam streaks and whitecaps and vary depending on wind-wave generation state. The idea of fractal dimension has resolved the problem of ocean state quantization. We can say also, that wave breaking field is self-similar at different storm conditions. A semiempirical rriridel was designed to desc r ibe the radiation-wind dependence of brightness temperature in the ocean-atmosphere s y s t e m . The concept of combined opticalmicrowave technique could be applied for investigation of global non-linear prr:cesses. wind-wave fetch and surge development in ocean.