Experimental study and theoretical model of high‐resolution radar backscatter from the sea

Lewıs, Bernard; Olin, Irwin D.

doi:10.1029/rs015i004p00815

Cited by 95 publications

(54 citation statements)

References 5 publications

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“…The pdf approach has been used, for instance, in microwave-based maritime surveillance and target detection [21], [22] but only recently with 0196-2892/$26.00 © 2011 IEEE optical data [23]. In addition, there is some previous work examining simultaneous signals in optical and microwave sensors [17], [24], [25]. However, the procedures for wave breaking identification have been fairly qualitative, and a high level of uncertainty persists.…”

Section: Introductionmentioning

confidence: 99%

Optical and Microwave Detection of Wave Breaking in the Surf Zone

Catalán¹,

Haller

Holman

et al. 2011

IEEE Trans. Geosci. Remote Sensing

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Abstract-Synchronous and colocated optical and microwave signals from waves in the surf zone are presented and analyzed. The field data were collected using a high-resolution video system and a calibrated horizontally polarized marine radar during the decaying phase of a storm. The resulting changes in the received signals from varying environmental conditions were analyzed. The analysis of the optical signal histograms showed functional shapes that were in accordance with the expected imaging mechanisms from the breaking and nonbreaking waves. For the microwave returns, the histogram shape showed a little dependence on the environmental parameters and exhibited an inflexion point at high returned power that is attributed to a change in the scattering mechanism. The high intensity signals were clearly associated with active wave breaking. However, with either sensor, it can be difficult to effectively isolate the wave breaking signature from other sources, such as a remnant foam or the highly steepened nonbreaking waves. A combined method was developed using the joint histograms from both sensors, and it is shown to effectively discriminate between active breaking, remnant foam, and steepened waves. The new separation method allows a further analysis of the microwave scattering from the breaking waves and a better quantification of the length scales of the breaking wave roller and the spatial/temporal distribution of wave breaking and wave dissipation in the surf zone.

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Section: Introductionmentioning

confidence: 99%

Optical and Microwave Detection of Wave Breaking in the Surf Zone

Catalán¹,

Haller

Holman

et al. 2011

IEEE Trans. Geosci. Remote Sensing

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“…Comparatively few have attempted to relate backscatter specifically to measures of wave breaking. Lewis and Olin, [1980] used combined video and radar measurements to study shallow water breaking waves from the shore. Keller et al [1986] reported characteristic Doppler signatures of breaking events from CW scatterometers at moderate incidence.…”

Section: Introductionmentioning

confidence: 99%

Space‐time properties of radar sea spikes and their relation to wind and wave conditions

Frasier¹,

Liu²,

McIntosh³

1998

J. Geophys. Res.

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Abstract. Low-grazing angle (LGA) radar sea spikes were observed with a highresolution, dual-polarization, X band imaging radar deployed on the floating instrument platform (FLIP) during the Marine Boundary Layer Experiment (MBLEX) held off the California coast during April-May 1995. Spatiotemporal statistics of observed sea spike events are presented, including duration, velocity, and directional distributions. The dependence of these parameters on wind and wave conditions is compared to theoretical predictions and to similar measurements of breaking wave signatures obtained with passive acoustic techniques by Ding and Farmer [1994]. The density of sea spikes (events per unit time per unit area) and the fractional surface coverage are estimated as a function of friction velocity and compared to theoretical predictions. Though we find consistency between the dynamical aspects of sea spike events and of acoustic wavebreaking signatures, we do not observe a predicted cubic u, dependence of sea spike density. Differences may be a consequence of the specific nature of low-grazing angle scattering at X band (and higher) frequencies. We observe an approximately quadratic dependence on u, of sea spike fractional surface coverage which is insensitive to the choice of backscattered power threshold over a 9 dB range. IntroductionBreaking waves on the ocean surface are believed to be an important part of air-sea interactions. They limit the height of ocean waves, mix surface waters, transfer energy from the wave field to currents, and enhance the fluxes of heat, mass, and momentum through the generation of turbulence and entrainment of air [Melville, 1996]. Because wave breaking is a nonlinear and intermittent process, direct measurement of wave breaking in the field is extremely difficult. For this reason the development of optical, acoustical, and microwave remote sensing methods is desirable.Breaking events have long been attributed as a source for microwave backscatter, especially for horizontally polarized radiation at near-grazing angles [Wetzel, 1990]. "Sea spikes," the colloquial term for high-intensity bursts of radar backscatter typically observed at low grazing angles, are attributable both to actively breaking waves and to scattering features (i.e., wedges, bores, plumes) bound near the crests of steep waves. A number of radar studies of wave breaking in the laboratory have attempted to identify the specific mechanisms for scattering and to measure the dependence of the microwave signature on breaking strength. Kwoh and Lake [1984] attributed discrete bursts of backscatter from short gravity waves at moderate to high incidence angles to "gentle" breaking. Banner and Fooks [1990, 1991a, b] used a CW scatterometer and boresighted video to study both the detection of breaking waves and the dependence on environmental parameters. They found an approximately cubic relation between u, and the number of sea spikes observed at moderate incidence attributable to breaking, in agreement with theoretical predictions by ...

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“…According to the photographs and data taken in the field experiments [14,24], the single sharply crested unbroken wave can be approximately simulated with the dihedral wedge of finite length shown in Figure 1. Different from the infinite two-dimensional wedge in the previous literatures, the dihedral wedge is characterized by internal angle β, length d, width 2l and height h. Since the size of the wave crest is related to incidence microwave, d and 2l are presented in wavelength of incidence wave λ.…”

Section: Wedge-like Breaking Wavementioning

confidence: 99%

“…Although the sea surface scattering is successfully modeled based on the Bragg theory in small and moderate incidence angles [6][7][8][9][10][11][12][13], some discrepancies between the predictions and experiment observations still cannot be explained. The terminology "super events" refers to the special phenomenon observed from the measured sea clutters, which includes sea spikes [14], polarization independence [15], faster scatters [16] and expanded width of Doppler spectrum [17].…”

Section: Introductionmentioning

confidence: 99%

Investigation of Low-Grazing-Angle Microwave Backscattering From Threedimensional Breaking Sea Waves

Luo¹,

Zhang²,

Wang³

et al. 2011

PIER

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Abstract-The microwave backscattering of the sea surface is investigated with the wedge-shaped breaking waves for the super events at low grazing angles (LGA). According to the relationship between the wave breaking and the whitecap, the finite three-dimensional wedges are utilized to approximately model the breaking waves, of which the spatial distribution is simulated with whitecap coverage. The phasemodified two-scale method (TSM) and method of equivalent currents (MEC) are used to calculate the surface and volume scattering of sea surface and breaking waves respectively. The sea spikes in LGA are observed by this model, and the strong directionality is caused by the breakers. Considering the Bragg phase velocity, orbital motion of facets and wind drift, the Doppler spectrum is simulated with the time series of sea clutter. Included the breaking waves, the scattering model indicates that the enhanced non-Bragg scattering leads to the extended Doppler spectrum width. The numerical results agree with the measured data well at LGA. Compared with the statistical models, the complex physical mechanism of the sea scattering is explicitly described in this paper.

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Experimental study and theoretical model of high‐resolution radar backscatter from the sea

Cited by 95 publications

References 5 publications

Optical and Microwave Detection of Wave Breaking in the Surf Zone

Optical and Microwave Detection of Wave Breaking in the Surf Zone

Space‐time properties of radar sea spikes and their relation to wind and wave conditions

Investigation of Low-Grazing-Angle Microwave Backscattering From Threedimensional Breaking Sea Waves

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