Skin depth at microwave frequencies of sea foam layers with vertical profile of void fraction

Anguelova, Magdalena D.; Gaiser, P.W.

doi:10.1029/2011jc007372

Cited by 39 publications

(50 citation statements)

References 42 publications

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“…In addition, as reported in [26], the skin depth in the foam layer is larger than that in pure seawater. Considering these, the plots in Fig.…”

Section: Absorption Coefficients Of Foam Layersupporting

confidence: 61%

A Numerical Study on Physical Characterizations of Microwave Scattering and Emission From Ocean Foam Layer

Jiang¹,

Xu²,

Chen³

et al. 2017

PIER B

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Abstract-This paper presents a numerical study of microwave scattering and emission from a foamcovered ocean surface. The foam layer is modeled as an inhomogeneous layer with randomly rough airfoam and foam-seawater boundaries. Kelvin's Tetrakaidecahedron structure is selected as the skeleton for simulating the air bubbles in the foam layer. The electromagnetic characteristics of the foam layer, including absorption and scattering coefficients for both vertical and horizontal polarizations, are calculated using a multilevel volume UV fast algorithm to accelerate the numerical computation of three dimensional Maxwell's equations. The surface scattering at air-foam and foam-seawater interfaces is determined using the integral equation model (IEM). The microwave emission from the foam-covered ocean surface, which accounts for multiple incoherent interactions within the foam layer and between the foam and interfaces, is modeled using the vector radiative transfer approach and numerically solved using the matrix doubling method. The model analyses of volume scattering and absorption of the foam layer reveal that the volume scattering coefficient of a foam layer increases with increasing water fraction at all selected frequencies, and its polarization dependence is negligible at a water fraction less than 2%. At 10.8 GHz and 18 GHz, the H-polarized scattering coefficient is smaller than the Vpolarized scattering coefficient for a larger water fraction; the opposite occurs at 36.5 GHz, at which V polarized scattering is weaker compared to H-polarized scattering. The model analyses of emission from a foam-covered ocean surface reveal that the emissivities at all selected operating frequencies have similar dependencies with water fraction and frequency, and they exhibit different sensitivities to water fractions. Moreover, the emissivities at high operating frequencies exhibit higher sensitivities to water fractions than the lower ones.

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“…In addition, as reported in [26], the skin depth in the foam layer is larger than that in pure seawater. Considering these, the plots in Fig.…”

Section: Absorption Coefficients Of Foam Layersupporting

confidence: 61%

A Numerical Study on Physical Characterizations of Microwave Scattering and Emission From Ocean Foam Layer

Jiang¹,

Xu²,

Chen³

et al. 2017

PIER B

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“…A connection between the thickness of the foam layer and the microwave properties is provided in [11,21]. According to these results, it can be assumed that σ f is equal to a constant, and very low, backscattering value; as it is very well known for very strong winds, when the sea surface is entirely covered by foam, the vertical average backscattering coefficient reduces to a very low value, which obviously coincides with the local backscattering of the foam.…”

Section: Methodsmentioning

confidence: 95%

Numerical Simulation of Whitecaps and Foam Effects on Satellite Altimeter Response

2014

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Abstract:The determination of wave height by active satellite remote sensing, be it Synthetic Aperture Radar (SAR) or altimeter, has been a common practice for many years and is now imbedded on many meteorological and oceanographic forecasting systems. Despite their differences, all active sensors are based on the measurement of the Normalized Radar Cross Section (NRCS) of the sea surface, i.e., of its backscattering properties, which in turn depend on the wind velocity. At small and moderate wind speeds, the main mechanism is the formation of ripples (small scale waves); at higher speeds, whitecaps appear, and foam starts playing an essential role in determining NRCS. In the past few years much research effort has gone into clarifying these effects, thus improving the general quality of the measurements. Little work, however, has been devoted so far to consider the vertical spatial variation of backscattering properties, and in particular of the floating foam, over the sea surface. As it is shown in the present paper, the shape of the backscattered electromagnetic impulse in radar altimeters depends on the spatial distribution of foam over the water height in the sea waves and therefore the performance of these instruments in determining Significant Wave Height (H s ) and Sea Surface Level (SSL) is strongly affected by this effect. This work tackles these problems by making use of specially implemented numerical algorithms to simulate both sea surface processes and radar altimeter techniques. Results show that some causes of errors can be better understood and eventually corrected: in particular, the paper deals with the reconstruction of the electromagnetic Sea State Bias (SSB), the well known altimeter ranging error due to the presence of ocean waves on the sea surface.

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“…For passive remote sensing of the ocean surface, the foam skin depth dictates our interest in the floating foam layers, excluding deeper bubble plumes [25]. Whitecaps corresponding to the inception of wave breaking are usually thick and bright (visually and radiometrically) and are referred to as active whitecaps.…”

Section: Sea Foam As a Mediummentioning

confidence: 99%

“…It was shown that various functional forms could represent the shape of the void fraction profile in the foam depth [25]. A review of oceanographic data from laboratory and field experiments [25] established a plausible range of foam layer thicknesses encountered in the ocean, from 1 cm to more than 12 cm in active whitecaps and from 0.1 to 1 cm when the whitecaps decay.…”

Section: Sea Foam As a Mediummentioning

confidence: 99%

“…Anguelova [24] analyzed the available information to determine suitable formula to predict the complex permittivity of sea foam ε f . Anguelova and Gaiser [25] focused on the skin depth of foam layers with a vertical void fraction profile. In the present paper, we consider the foam properties at microwave frequencies, which control fundamental radiative processes such as reflection, scattering, and transmission in vertically structured foam layers.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

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

Anguelova

Gaiser

2012

Remote Sensing

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Foam fraction can be retrieved from space-based microwave radiometric data at frequencies from 1 to 37 GHz. The retrievals require modeling of ocean surface emissivity fully covered with sea foam. To model foam emissivity well, knowledge of foam properties, both mechanical and dielectric, is necessary because these control the radiative processes in foam. We present a physical description of foam dielectric properties obtained from the foam dielectric constant including foam skin depth; foam impedance; wavelength variations in foam thickness, roughness of foam layer interfaces with air and seawater; and foam scattering parameters such as size parameter, and refraction index. Using these, we analyze the scattering, absorption, reflection and transmission in foam and gain insights into why volume scattering in foam is weak; why the main absorption losses are confined to the wet portion of the foam; how the foam impedance matching provides the transmission of electromagnetic radiation in foam and maximizes the absorption; and what is the potential for surface scattering at the foam layers boundaries. We put all these elements together and offer a conceptual understanding for the high, black-body-like emissivity of foam floating on the sea surface. We also consider possible scattering regimes in foam.

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Skin depth at microwave frequencies of sea foam layers with vertical profile of void fraction

Cited by 39 publications

References 42 publications

A Numerical Study on Physical Characterizations of Microwave Scattering and Emission From Ocean Foam Layer

A Numerical Study on Physical Characterizations of Microwave Scattering and Emission From Ocean Foam Layer

Numerical Simulation of Whitecaps and Foam Effects on Satellite Altimeter Response

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

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