Combined analysis of the radar cross‐section modulation due to the long ocean waves around 14° and 34° incidence: Implication for the hydrodynamic modulation

Hauser, Danièle; Caudal, G.

doi:10.1029/96jc02124

Cited by 17 publications

(5 citation statements)

References 21 publications

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“…During the most recent campaigns (SEMAPHORE in 1993, FETCH in 1998), it was also operated in a mode allowing to measure σ 0 hh in the range 27° < θ < 41°. By combining these different modes of operation, a method was also developed to deduce the hydrodynamic MTF near 30° incidence angle [ Hauser and Caudal , 1996].…”

Section: Results Of the Full Model Compared To Observationsmentioning

confidence: 99%

A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model

Kudryavtsev

Hauser²,

Caudal³

et al. 2003

J. Geophys. Res.

250

388

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[1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross-section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations and wind wave conditions. We have developed a physical model that takes into account, not only the Bragg mechanism, but also the non-Bragg scattering mechanism associated with wave breaking. A single model was built to explain on the same physical basis both the background behavior of the NRCS and the wave radar Modulation Transfer Function (MTF) at HH and VV polarization. The NRCS is assumed to be the sum of a Bragg part (two-scale model) and of a non-Bragg part. The description of the sea surface is based on the short wind wave spectrum (wavelength from few millimeters to few meters) developed by Kudryavtsev et al. [1999] and wave breaking statistics proposed by Phillips [1985]. We assume that non-Bragg scattering is supported by quasi-specular reflection from very rough wave breaking patterns and that the overall contribution is proportional to the white cap coverage of the surface. A comparison of the model NRCS with observations is presented. We show that neither pure Bragg nor composite Bragg model is able to reproduce observed feature of the sea surface NRCS in a wide range of radar frequencies, wind speeds, and incidence and azimuth angles. The introduction of the non-Bragg part in the model gives an improved agreement with observations. In Part 2, we extend the model to the wave radar MTF problem.

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Section: Results Of the Full Model Compared To Observationsmentioning

confidence: 99%

A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model

Kudryavtsev

Hauser²,

Caudal³

et al. 2003

J. Geophys. Res.

250

388

View full text Add to dashboard Cite

show abstract

“…During the FETCH experiment, RESSAC was also operated in a second mode to observe the surface in the incidence range 27° < θ < 41°: the antenna was fixed on one side of the airplane while this latter was performing circles with a roll of about 20°. By combining these two different modes of operation, Hauser and Caudal [1996] developed a method to estimate the hydrodynamic MTF near 30° incidence angle. The total MTF is estimated at incidence 30° from the ratio of the radar modulation spectrum to the directional wave slope spectrum (derived from the first mode of operation).…”

Section: Comparison With Radar Observationsmentioning

confidence: 99%

A semiempirical model of the normalized radar cross section of the sea surface, 2. Radar modulation transfer function

et al. 2003

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[1] Multiscale composite models based on the Bragg theory are widely used to study the normalized radar cross section (NRCS) over the sea surface. However, these models are not able to correctly reproduce the NRCS in all configurations. In particular, even if they may provide consistent results for vertical transmit and receive (VV) polarization, they fail in horizontal transmit and receive (HH) polarization. In addition, there are still important discrepancies between model and observations of the radar modulation transfer function (MTF), which relates the modulations of the NRCS to the long waves. In this context, we have developed a physical model that takes into account not only the Bragg mechanism but also the non-Bragg scattering associated with radio wave scattering from breaking waves. The same model was built to explain both the background NRCS and its modulation by long surface wave (wave radar MTF problem). In part 1, the background NRCS model was presented and assessed through comparisons with observations. In this part 2, we extend the model to include a third underlying scale associated with longer waves (wavelength $10-300 m) to explain the modulation of the NRCS. Two contributions are distinguished in the model, corresponding to the so-called tilt and hydrodynamic MTF. Results are compared to observations (already published in the literature or derived from the FETCH experiment). As found, taking into account modulation of wave breaking (responsible for the non-Bragg mechanism) helps to bring the model predictions in closer agreement with observations. In particular, the large MTF amplitudes for HH polarization (much larger than for VV polarization) and MTF phases are better interpreted using the present model.

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“…In practice m(x,ϕ) is obtained by removing a low order polynomial fit from the measured radar power profile, thus eliminating the trend and retaining only the modulations. The sea wave polar-symmetric height spectrum F(k,ϕ) is then obtained from the expression (Jackson et al, 1985a;Hauser and Caudal, 1996):…”

Section: Measurement Of the Sea Wave Spectrummentioning

confidence: 99%

KuROS: A New Airborne Ku-Band Doppler Radar for Observation of Surfaces

Caudal

Hauser

Valentin

et al. 2014

Journal of Atmospheric and Oceanic Technology

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Abstract. We present the new airborne Doppler radar KuROS (Ku-band Radar for Observation of Surfaces), which provides measurements of the normalized radar cross section σ° and of the Doppler velocity over the sea. The system includes two antennae rotating around a vertical axis, although only the results from the lower incidence (14°) antenna are presented here. We also give first results from observations performed during two field campaigns held in 2013 (HyMeX and PROTEVS campaigns). Sea wave directional spectra computed by the radar from tilt modulation of σ° are consistent with those given by the directional wave rider moored in the Mediterranean basin, both in terms of significant wave height H s and main features of the wavenumber spectrum. As concerns the azimuthal distribution, two methods are tested to remove the 180° ambiguity of the radar derived directional spectrum. The first method is based on the correlation between the modulations of σ° and Doppler velocity, which reflects the correlation between sea surface slope and orbital velocity. The second method does not use the Doppler velocity, but computes the cross-spectrum between the modulations of σ° between two power profiles separated by some time lag ΔT, from which the phase velocity of sea waves is deduced. Comparing the sea wave directional spectra disambiguated by both methods, with the directional spectrum given by the wave rider, we conclude that the first method (using Doppler velocity) is more efficient to remove the 180° ambiguity, and should be preferred to the second method.3

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Combined analysis of the radar cross‐section modulation due to the long ocean waves around 14° and 34° incidence: Implication for the hydrodynamic modulation

Cited by 17 publications

References 21 publications

A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model

A semiempirical model of the normalized radar cross‐section of the sea surface 1. Background model

A semiempirical model of the normalized radar cross section of the sea surface, 2. Radar modulation transfer function

KuROS: A New Airborne Ku-Band Doppler Radar for Observation of Surfaces

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