Characteristics of SFH scattering at breaking sea waves

Kalmykov, A. I.; Kurekin, A. S.; Lementa, Yu. A.; Ostrovskii, I. E.; Pustovoitenko, V. V.

doi:10.1007/bf01044049

Cited by 5 publications

(6 citation statements)

References 3 publications

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“…However, it must be noted that the present data have been obtained at lower grazing angles (less than 3.5°). To put the data in context, a summary of previous nearshore observations and the present data set are presented in Figure [ Kalmykov et al ., ; Lewis and Olin , ; Haller and Lyzenga , ; Farquharson et al ., ]. We have also included one laboratory data set by [ Coakley et al ., ], and data taken at 3° grazing by McLaughlin et al .…”

Section: Discussionmentioning

confidence: 97%

“…The exceptions are the data by Kalmykov et al . [], which exceeds significantly the values observed here at similar grazing angles. Although, we note that those data were collected as waves broke over a breakwater, and were challenged to explain the scattering mechanism responsible for such high NRCS values.…”

Section: Discussionmentioning

confidence: 99%

“…Moreover, it is indicative that the overall scattering from the active breaking portion of the wave shows a clear dependency on grazing angle, but no polarization dependency. While it is accepted that several scattering mechanisms can coexist during the breaking cycle studied here, the obvious source of scattering from the active breaking portion is that of a very rough surface [ Kalmykov et al ., ; Lewis and Olin , ; Coakley et al ., ], which is generated mechanically by the breaking process. Its NRCS is not directly dependent on environmental conditions and can yield similar scattering levels for both polarizations, hence, polarization ratios close to unity.…”

Section: Discussionmentioning

confidence: 99%

“…Among the earliest observations are those of Kalmykov et al . [] who attempted to relate the observed backscatter to the production of droplets by breaking waves. Lewis and Olin [] using a dual‐polarized X‐band sensor at 5° grazing found that sea spikes were well correlated with whitewater formation observed on synchronous optical data.…”

Section: Introductionmentioning

confidence: 99%

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Microwave backscattering from surf zone waves

Catalán

Haller

Plant

2014

J. Geophys. Res. Oceans

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The microwave backscatter properties of surf zone waves are analyzed using field observations. By utilizing a preexisting, independent, water surface discrimination technique, the microwave returns were extracted along individual waveforms and the data from shoaling (steepening) waves, surf zone breaking waves, and remnant foam were separated and quantified. In addition, a wave tracking analysis technique allows the returns to be examined on a wave-by-wave basis as individual waves progress through the shoaling zone and break on a nearshore sand bar. Normalized radar cross sections (NRCS), polarization ratios, Doppler spectra, and scatterer velocities were collected using a dual-polarized, X-band radar operating at lower grazing angles than previously reported (1 -3.5 ). The results indicate that the maximum NRCS levels are from the active breaking portions of the wave and were consistently about 220 dB, regardless of radar polarization, azimuth angle, wave height, or wind speed. In addition, breaking waves induce broadening of the Doppler spectra and mean scatterer velocities that correlate well with the carrier wave celerity. Analysis of the polarization ratios suggest that the active breaking portions of the wave are depolarized but that higher polarization ratios (>0 dB) are found on the leading edges shoreward of the active breaking portions of the waves, which indicates a clear distinction between two scattering regimes. These results are consistent with scattering from a very rough surface that is being mechanically generated by the breaking process, showing a good agreement with the expected grazing angle dependency of a Lambertian scatterer.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Microwave backscattering from surf zone waves

Catalán

Haller

Plant

2014

J. Geophys. Res. Oceans

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“…For radar backscattering studies, field data on sea spray impacts radar are scarce, especially for Ka-band measurements. Field measurements of surf breakers [35] generally correspond to enhanced radar backscatter events within the tail of Doppler spectra. Later, the dominant role of surface backscattering was revealed and the sea spray role downscaled [36].…”

Section: Introductionmentioning

confidence: 99%

Ka-Band Doppler Scatterometry: A Strong Wind Case Study

et al. 2022

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Global joint measurements of sea surface winds and currents are planned using satellite-based Doppler scatterometers operating in the Ka-band to achieve improved spatial resolution and retrieval accuracy. Still, the knowledge of sea surface Ka-band backscatter properties is poor, particularly, at high winds (>20 m s−1). Sea surface radar cross-section in the Ka-band, in contrast to that in the lower frequency Ku-/X-/C-/L-bands, is likely more sensitive to sea spray, small-scale particles typically present at high winds. In this paper, tower-based field data collected by a continuous dual-co-polarized Ka-band radar during a strong offshore wind event (with wind speed reaching 33 m s−1) are analyzed. This katabatic wind event (≈12 h long) was also recorded by supplementary wave, wind, and current sensors. At the wave fetch of ≈1 km, the maximum wavelength of observed offshore waves was ≈10 m. For such extremely young wind–sea conditions, an apparent sea spray generation was observed during wind gusts. Radar measurements were performed at 20∘ and 45∘ incidence angles, mostly for cross- and up-wind azimuth look geometry. Based on these high wind measurements, the previously developed Ka-band empirical model is tested and compared with other published geophysical model functions. Dual-co-polarized measurements are used to infer resonant Bragg and non-Bragg scattering components and assess the short wind wave spectrum, which shows a clear tendency for saturation at high winds. The presence of sea spray signatures is apparent in the high-frequency tails of radar Doppler spectra, but their overall contribution to the Doppler centroid frequency is weak. Hence, the standard modulation transfer function approach developed for moderate winds is still applicable at high winds for interpreting the wave-induced Doppler velocity and inferring sea surface currents. These results can also be useful for understanding Doppler scatterometry measurements in tropical cyclones.

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Springer Praxis Books

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Characteristics of SFH scattering at breaking sea waves

Cited by 5 publications

References 3 publications

Microwave backscattering from surf zone waves

Microwave backscattering from surf zone waves

Ka-Band Doppler Scatterometry: A Strong Wind Case Study

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