Measurements of Sea Clutter at Low Grazing Angle in Mediterranean Coastal Environment

Fabbro, Vincent; Biegel, Gregor; Förster, Jörg; Poisson, Jean-Baptiste; Danklmayer, Andreas; Bohler, Christian Onno; Marcellin, Jean-Paul; Brehm, Thorsten; Gallus, Michael; Castanet, Laurent; Ulland, Andreas; Hurtaud, Yvonick

doi:10.1109/tgrs.2017.2727057

Cited by 14 publications

(10 citation statements)

References 20 publications

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“…In the following, we will focus our attention on the case where the radar beam propagates in the direstion of the wind. In these conditions, k lies along this direction and the quantity A ( K ) A * ( K−k ) that contributes to the group line takes significant values when K is also directed in this direction and decays rapidly away from it, as shown in Figure for typical weather conditions encountered during data measurements Fabbro et al (). In addition, since ω =Ω( K )−Ω( K−k ) is an even function of K ⊥ , the component of K perpendicular to k , we have

\frac{\partial ω}{\partial K_{⊥}} false(K_{⊥} = 0 false) = 0

.…”

Section: Group Linementioning

confidence: 99%

“…Obviously, the same result holds for the square of the slope, since only A(K) is modified in this case. Diagrams from real data, such as the one in Figure 2 computed through a 2D FFT of range-time series from the database described in Fabbro et al (2017), do exhibit a cloud of energetic points at low space and time frequencies. The boundaries of the group line do not clearly appear, because of noise, of poor resolution, and of the direction spreading of gravity waves.…”

Section: Group Linementioning

confidence: 99%

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Two‐Dimensional Spectra of Radar Returns from Sea: 1. Theoretical and Numerical Study of the Group Line

2019

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The work presented here aims at interpreting the pattern observed at low frequencies in wavenumber-frequency (k, ) representations (dispersion diagrams) of radar returns from sea surface. This pattern is sometimes referred to as the "group line" in the literature and is supposed to result from the nonlinear behavior of the signal with respect to surface profile. To confirm this assumption, we have calculated the patterns generated by various nonlinear terms of second order in sea surface height. It is shown that the resolution in frequency of most data is not sufficient to allow for an accurate representation of the group line through an FFT. A methodology is proposed to define an average slope of the group line, which can be interpreted in terms of velocity.

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\frac{\partial ω}{\partial K_{⊥}} false(K_{⊥} = 0 false) = 0

.…”

Section: Group Linementioning

confidence: 99%

Section: Group Linementioning

confidence: 99%

Two‐Dimensional Spectra of Radar Returns from Sea: 1. Theoretical and Numerical Study of the Group Line

2019

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“…The analysis presented in this paper is based on MARLENE campaign, which has been described in Fabbro et al (), together with some analysis of reflectivity and Doppler spectra. The data were obtained in May 2014 with three radar systems called MEMPHIS, MARSIG, and MEDYCIS, deployed on the French south coast.…”

Section: Description Of the Experimentsmentioning

confidence: 99%

“…Environmental and oceanographic conditions were recorded by the WTD71 RV‐PLANET ship during the experiment, providing in particular the surface height, the dominant wave time period, and the wind direction. For more details about MARLENE experiment the reader can refer to Fabbro et al ().…”

Section: Description Of the Experimentsmentioning

confidence: 99%

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Two‐Dimensional Spectra of Radar Returns From Sea: 2. Analysis of the Group Line From Experimental Data

2019

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Wavenumber-frequency spectra are obtained by performing a two-dimensional Fourier transform of range-time normalized radar cross-section (NRCS) or Doppler velocity maps. In such diagrams, some energy is present at low space-time frequencies, resulting from the nonlinear behavior of the measured quantity related to the sea surface geometry. This feature is called the group line, since for a narrow-band wave packet the energy is concentrated along a straight line with group velocity as slope. Which physical nonlinear process generates the group line remains an open question. Breaking waves have been proposed as the most probable contributor. However, numerical simulations from weakly nonlinear surfaces without breaking events and experiments performed at low winds also provide such feature. In a companion paper, a theoretical and numerical analysis has permitted to predict the energy distribution of the group line depending on the kind of nonlinearity. It provides some means to characterize a group line in a rigorous way. In this paper, it is used to analyze the group lines derived from the experimental MARLENE data. The group lines computed from the backscattering amplitude behave as the one of the square of sea surface slopes. The analysis of the Doppler velocities provides similar results, which significantly differ from what is expected if breaking waves are the main contributors and do break at velocities reported in the literature. Our results suggest that the group line mainly reflects the asymptotic behavior of the scattering amplitude at grazing incidence, of which the leading nonlinear term is proportional to the square of surface slope.

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Analysis of UHF-band sea clutter reflectivity at low grazing angles in offshore waters of the Yellow Sea

Shui

Xia

et al. 2020

International Journal of Remote Sensing

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Measurements of Sea Clutter at Low Grazing Angle in Mediterranean Coastal Environment

Cited by 14 publications

References 20 publications

Two‐Dimensional Spectra of Radar Returns from Sea: 1. Theoretical and Numerical Study of the Group Line

Two‐Dimensional Spectra of Radar Returns from Sea: 1. Theoretical and Numerical Study of the Group Line

Two‐Dimensional Spectra of Radar Returns From Sea: 2. Analysis of the Group Line From Experimental Data

Analysis of UHF-band sea clutter reflectivity at low grazing angles in offshore waters of the Yellow Sea

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