Macroscopic Foam-Spray Models for Ocean Microwave Radiometry

Abstract

We continue to develop combined microwave models of dispersed foam-spray media for ocean remote sensing. In this paper, more attention is focused on the structure hierarchy of dispersed systems and their electromagnetic nonuniformity. The basic variable parameter is the vertical profile of the effective complex dielectric constant that is associated with two-phase stratification of thick foam layers. Wet foam is modeled by monoand polydispersed systems of bubbles (i.e., two-layer spherical particles with water shells); dry foam is represented by a statistical two-phase mixture, containing thin water films and air. Spray, located above the foam, is modeled by a cloud of spherical water droplets. The impact of different microstructure parameters and effective profiles on the emissivity is analyzed numerically using an iterative multi-layer computer simulation technique. Examples of our modeling are presented in the paper.

Emissivity Measurements of Foam-Covered Water Surface at L-Band for Low Water Temperatures

“…Anguelova [3] systematically investigated well-known effective permittivity formulae of composite media according their applicability to the sea foam layer. To investigate the emissivity increment induced by a foam-covered sea surface, theoretical models [8][9][10][11][16][17][18][19][20][21] were developed with electromagnetic wave theory, microwave vector radiative transfer equation (VRTE), and EMA theory. For instance, Guo et al [17] investigated the influence of foam microstructures, microwave frequency and foam-layer thickness on the emissivity of a foam-covered sea surface with quasi-crystalline approximation and VRTE, by treating the foam as densely packed air bubbles coated with seawater.…”

“…For the AVF with vertical distribution in a foam layer, Wei [10] proposed an EMA method to estimate foam emissivity of a non-uniform AVF. Similarly, Anguelova et al [5] and Raizer [21] presented a radiative transfer model for estimating the emissivity of a vertically structured foam layer at microwave frequencies. Although the aforementioned theoretical models have demonstrated the influence of foam structures on emissivity, it is still difficult to calculate foam layer emissivity.…”

Modeling of L-band Foam Emissivity and Impact on Surface Salinity Retrieval

“…However, at L-and S-bands it is reasonable to apply a macroscopic electromagnetic theory of random heterogeneous mixtures adapted for stratified two-phase media. In particular, our microwave model reported in [6] operates with vertical profiles of the effective complex permittivity which are parameterized by surface temperature and salinity. The profile is a variable function of volume (bulk) concentrations and dielectric constants of phase components (i.e., air and water).…”

Dielectric and Radiative Properties of Sea Foam at Microwave Frequencies: Conceptual Understanding of Foam Emissivity

“…We identify these sublayers by their f a values with vertical lines in Figure 3. While we base this conceptual representation on different rates of change of λ f values, Raizer (Figure 1(a) in [39]) gives a similar schematic of a vertically stratified foam based on experimental observations [28].…”