Critical phenomena with the thermal radio irradiation of a periodically uneven water surface

Étkin, V. S.; Vorsin, N. N.; Kravtsov, Yu. A.; Mirovskii, V. G.; Никитин, В. В.; Popov, Alexey; Troitskii, I. A.

doi:10.1007/bf01031700

Cited by 16 publications

(4 citation statements)

References 2 publications

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“…predicts potential "critical phenomena" [4] that can occur to produce rapid changes in brightness temperatures versus angle. The results of Figure 7 illustrate such behaviors for observation angles around 30 • .…”

Section: Resultsmentioning

confidence: 99%

Higher ORDER Emission Model Study of Bi-sinusoidal Surface Brightness Temperatures

Johnson¹

2002

PIER

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Models for microwave thermal emission from a rough surface are currently of interest due to the goal of improved sea surface wind vector retrievals from polarimetric brightness temperature measurements. Models based on either a small slope approximation or on a physical optics approach have been proposed and have shown some success in matching observations. Both of these models involve series solutions, but computation of higher order terms typically is difficult, particularly for multi-scale sea surface models. Knowledge of higher order term contributions, however, would assist in understanding the limitations of the low-order methods applied in practice. In this paper, higher order results from both the small slope and physical optics methods are studied and compared for a simple bi-sinusoidal surface model (i.e. height profile = A sin(2πx Px) sin(2πy Py), where P x and P y are the surface periods in the x and y directions, respectively). Results show both methods to provide good predictions for moderate slope "large scale" surfaces (i.e. periods large compared to the observing electromagnetic wavelength) when shadowing and multiple scattering effects are negligible, while only the small slope theory correctly predicts emission from "small scale" profiles. The influence of both shadowing and multiple scattering effects is examined, and the "binary" shadowing behavior used in the physical optics method is suggested as a source of larger errors observed as shadowing effects increase.

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Section: Resultsmentioning

confidence: 99%

Higher ORDER Emission Model Study of Bi-sinusoidal Surface Brightness Temperatures

Johnson¹

2002

PIER

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“…However, for length scales comparable to the electromagnetic wavelength, several resonance type behaviors are observed, particularly at larger observation angles. These resonance type behaviors can be attributed to a "critical phenomenon" effect [23], associated with scattered waves making a transition from propagating to nonpropagating, i.e., crossing through 0 and becoming imaginary or reaching a minimum. Further study of this effect shows that only length scales in the ranges and Re can show critical phenomena; the vertical lines in the figures indicate the outermost boundaries of these limits and confirm that the resonance effects are associated with critical phenomena.…”

Section: Plots Of the Harmonic Weighting Functionsmentioning

confidence: 99%

Theoretical study of the small slope approximation for ocean polarimetric thermal emission

Johnson

Zhang

1999

IEEE Trans. Geosci. Remote Sensing

110

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Analytical models for ocean surface polarimetric thermal emission based on the small perturbation method (SPM) have shown success in matching brightness temperature azimuthal variations from aircraft based measurements. It has also been shown that use of the small perturbation method for calculation of surface emissivity results in a series in surface slope, not surface height, so that the method remains accurate for large height surface emission even when it fails for the corresponding scattering calculations. This paper presents a detailed analysis of the SPM/small slope approximation (SPM/SSA) for ocean surface polarimetric thermal emission, and investigates the extent to which varying ocean surface length scales contribute to brightness temperature zeroth and second azimuthal harmonics. It is found that ocean waves of lengths both comparable to and much greater than the electromagnetic wavelength can contribute to these harmonics, depending on the extent to which the ocean surface spectral model places asymmetry in these length scales. In addition, the SPM/SSA is approximated for the contributions of both very long and very short ocean length scales compared to the electromagnetic wavelength, and it is found that both long and short wave contributions can be expressed in simple equations involving either standard or modified ocean surface slope variances.Index Terms-Microwave readiometry, passive remote sensing.

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“…Foam effects are neglected, 3) The rough surface contribution to emissivity is assumed dominant at surface scale equal to electromagnetic wavelength,…”

Section: Discussionmentioning

confidence: 99%

“…For length scales comparable to the electromagnetic wavelength, several resonance type behaviors attributed to the "critical phenomenon" effect [3] are observed. As shown in Fig.…”

Section: A Weighting Functions Properties At Nadirmentioning

confidence: 97%

A simple algorithm for sea surface salinity retrieval from L-band radiometric measurements at nadir

Reul¹,

Chapron²

IGARSS 2003. 2003 IEEE International Geoscience and Remote Sensing Symposium. Proceedings (IEEE Cat. No.03CH37477)

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The Small Slope Approximation (SSA) theory is applied to the prediction of the foam-free sea surface brigthness temperatures at L-band and nadir incidence angle. If surface geometry is assumed to be gaussian, the wind induced polarized brightness temperature signals are integral functions of the product of the directional curvature spectrum harmonics and electromagnetic weighting functions. At nadir incidence angle, these electromagnetic weighting functions are equals in magnitude for horizontal and vertical polarization and exhibit peaky distribution as function of wavenumber. Using these properties together with azimuthal characteristics of the directional curvature spectrum at L-band, the combination of vertically and horizontally polarized brightness temperature signals at normal incidence is shown to form a simple linear equation of the dielectric constant, the SST and the wind direction. A simple analytical inversion algorithm is proposed to retrieve the Sea Surface Salinity without a priori knowledge of the wind speed using the previously established dependence.

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Critical phenomena with the thermal radio irradiation of a periodically uneven water surface

Cited by 16 publications

References 2 publications

Higher ORDER Emission Model Study of Bi-sinusoidal Surface Brightness Temperatures

Higher ORDER Emission Model Study of Bi-sinusoidal Surface Brightness Temperatures

Theoretical study of the small slope approximation for ocean polarimetric thermal emission

A simple algorithm for sea surface salinity retrieval from L-band radiometric measurements at nadir

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