Radar Backscattering from Non-Gaussian Sea Surface

To progress in the understanding of the impact of non-linear wave profiles in scattering from sea surfaces, a non-linear model for infinite depth gravity waves is considered. This model, termed the "Choppy Wave Model" (CWM), is based on horizontal deformation of a linear, reference random surface. It is numerically efficient and enjoys explicit second-order statistics for height and slope, which makes it well adapted to a large family of scattering models. We incorporate the CWM into a Kirchhoff or Small-Slope Approximation and derive statistical expressions for the corresponding incoherent cross section. We insist on the importance of "undressing" the wavenumber spectrum to generate a non-linear surface with a prescribed spectrum. Interestingly, the inclusion of non-linearities is found to be practically compensated by the spectral undressing process, an effect which might be specific to the CWM and needs to be investigated in the framework of fully non-linear models. Accordingly, the difference between the respective NRCS is rather small. The most noticeable changes are faster azimuthal variations and a slight increase of the radar returns at nadir. A statistical analysis of sea clutter in the framework of a Two-Scale Model is also performed at large but nongrazing incidence. It shows a pronounced polarization dependence of the distribution of large backscattered amplitudes, the tail being much larger in horizontal polarization and for small resolution cell. Surface non-linearities are shown to increase the tail of the amplitude distribution, as expected. Less obviously, their relative impact is found lesser in horizontal polarization. This raises the question of the actual contribution of non-linearities in radar sea spikes at nongrazing angles.

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Scattering From Nonlinear Gravity Waves: The “Choppy Wave” Model

Nouguier

Guérin

Chapron

2010

IEEE Trans. Geosci. Remote Sensing

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Numerical Computation of the Electromagnetic Bias in GNSS-R Altimetry

Ghavidel

Schiavulli

Camps

2016

IEEE Trans. Geosci. Remote Sensing

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In radar altimetry the electromagnetic (EM) bias is originated by the smaller reflectivity of wave crests than troughs, thus the average sea surface height is under-estimated. Bias uncertainty is currently the largest factor in altimetry error budgets. The EM bias in a bistatic forward-scattering configuration at L-band, such as in Global Navigation Satellite SystemsReflectometry (GNSS-R) altimetry, remains one of the major sources of uncertainty in the altimetry error budget. In this work the EM bias is computed using numerical simulations.To do so, a time-dependent synthetic non-Gaussian sea surface is created using the PiersonMoskowitz and Elfouhaily sea surface height spectra and spreading function. The sea surface is then discretized in facets and "illuminated" using a Right Hand Circular Polarization data at C-and Ku-bands. Then, the numerical model is applied at L-band, for bistatic configurations, including different azimuth angles, and different wind speeds. It is found that the EM bias is almost insensitive to the sea surface spectra selected and increases with increasing wind speed and incidence/scattering angle (up to ~20 cm at θi,s = 45° and U10 = 12 m/s), and it also exhibits a non-negligible azimuthal dependence, that must be accounted for in the error budgets of upcoming GNSS-R altimetry missions.

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Statistical Non-Gaussian Model of Sea Surface With Anisotropic Spectrum for Wave Scattering Theory. Part I - Abstract

Tatarskiǐ

Tatarskii

1999

Journal of Electromagnetic Waves and Applications

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Radar Backscattering from Non-Gaussian Sea Surface

Cited by 3 publications

References 8 publications

Scattering From Nonlinear Gravity Waves: The “Choppy Wave” Model

Scattering From Nonlinear Gravity Waves: The “Choppy Wave” Model

Numerical Computation of the Electromagnetic Bias in GNSS-R Altimetry

Statistical Non-Gaussian Model of Sea Surface With Anisotropic Spectrum for Wave Scattering Theory. Part I - Abstract

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