Microwave emissivity of sea foam layers with vertically inhomogeneous dielectric properties

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

doi:10.1016/j.rse.2013.07.017

Cited by 55 publications

(51 citation statements)

References 47 publications

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“…To adequately account for foam effects on brightness temperature or emissivity, one needs to understand the microwave electromagnetic properties of a foam layer, such as permittivity and emissivity. In fact, these two complex properties are not only related to foam microstructure parameters such as air volume fraction (AVF), foam layer thickness and size of seawater-coated air bubbles, but also microwave frequency, SST and SSS [5][6][7][8][9][10][11]. Although the sea foam layer can increase sea surface emissivity [12], this mechanism is not clearly understood, especially in calculating or predicting emissivity and permittivity of that layer.…”

Section: Introductionmentioning

confidence: 99%

“…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.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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For a foam-covered sea surface, it is difficult to retrieve sea surface salinity (SSS) with L-band brightness temperature (1.4 GHz) because of the effect of a foam layer with wind speeds stronger than 7 m/s, especially at low sea surface temperature (SST). With foam-controlled experiments, emissivities of a foam-covered water surface at low SST (−1.4 °C to 1.7 °C) are measured for varying SSS, foam thickness, incidence angle, and polarization. Furthermore, a theoretical model of emissivity is introduced by combining wave approach theory with the effective medium approximation method. 10914 the foam layer emissivity increments are discussed for frequencies between 1 and 37 GHz.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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“…Salisbury et al (2013) describe the basic points of the algorithm estimating W (hereafter referred to as the W (T B ) algorithm). Briefly, the algorithm obtains W by using measured T B data for the composite emissivity of the ocean surface and modeled T B data for the emissivity of the rough sea surface and areas that are covered with foam Anguelova and Gaiser, 2013). An atmospheric model is necessary to evaluate the contribution from the atmosphere to T B .…”

Section: Whitecap Databasementioning

confidence: 99%

Parameterization of oceanic whitecap fraction based on satellite observations

Albert

Anguelova

Manders

et al. 2017

2017 IEEE International Geoscience and Remote Sensing Symposium (IGARSS)

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Abstract. In this study, the utility of satellite-based whitecap fraction (W ) data for the prediction of sea spray aerosol (SSA) emission rates is explored. More specifically, the study aims at evaluating how an account for natural variability of whitecaps in the W parameterization would affect SSA mass flux predictions when using a sea spray source function (SSSF) based on the discrete whitecap method. The starting point is a data set containing W data for 2006 together with matching wind speed U 10 and sea surface temperature (SST) T . Whitecap fraction W was estimated from observations of the ocean surface brightness temperature T B by satellite-borne radiometers at two frequencies (10 and 37 GHz). A global-scale assessment of the data set yielded approximately quadratic correlation between W and U 10 . A new global W (U 10 ) parameterization was developed and used to evaluate an intrinsic correlation between W and U 10 that could have been introduced while estimating W from T B . A regional-scale analysis over different seasons indicated significant differences of the coefficients of regional W (U 10 ) relationships. The effect of SST on W is explicitly accounted for in a new W (U 10 , T ) parameterization. The analysis of W values obtained with the new W (U 10 ) and W (U 10 , T ) parameterizations indicates that the influence of secondary factors on W is for the largest part embedded in the exponent of the wind speed dependence. In addition, the W (U 10 , T ) parameterization is able to partially model the spread (or variability) of the satellite-based W data. The satellite-based parameterization W (U 10 , T ) was applied in an SSSF to estimate the global SSA emission rate. The thus obtained SSA production rate for 2006 of 4.4 × 10 12 kg year −1 is within previously reported estimates, however with distinctly different spatial distribution.

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“…Similar to the permittivity of the foam, the water fraction in the foam layer is difficult to measure directly. Similarly, the water fraction of the foam layer was assumed from 0 to 100% when the bubbles beneath the seawater (white water) were included [10]. The experimental results [5] reveal that the water fraction is approximately 5.0% at the top of the foam layer and 10.5% at the center of the foam layer.…”

Section: Parameters For Model Analysesmentioning

confidence: 99%

“…Raizer [8] developed a composite microwave model for estimating the emissivity of sea foam, by incorporating the vertical profile of an effective permittivity, which was associated with air-water stratifications. Anguelova and Gaiser [9,10] determined the effective permittivity of sea foam layers by comparing five kinds of mixing rules based on the effective medium theory; the importance of multiple interactions between air-foam and foamseawater interfaces was noted in their studies. To achieve more robust applications of microwave remote sensing of an ocean surface, more comprehensive physical characterizations of microwave scattering and emission from a foam-covered ocean surface are required, such as the study of surface roughness driven by wind over the ocean surface, interactions of the foam layer with the sea surface, and their effects on the directional wave spectrum of short gravity and capillary waves [11].…”

Section: Introductionmentioning

confidence: 99%

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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Microwave emissivity of sea foam layers with vertically inhomogeneous dielectric properties

Cited by 55 publications

References 47 publications

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

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

Parameterization of oceanic whitecap fraction based on satellite observations

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

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