Island connected sea bed signatures observed by multi-frequency synthetic aperture radar

Hennings, Ingo; Metzner, M.; Calkoen, C.J.

doi:10.1080/014311698215072

Cited by 9 publications

(9 citation statements)

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“…The reason for this is not clear. Hennings et al (1998) show that the eVect of velocity bunching is small compared to that of wave-current interaction, so this may not explain the disagreement. It may be possible that the action balance equation is not applicable in situations with current gradients as strong as considered here, since it was derived under the assumption that the current remains almost constant over one wave length.…”

Section: Comparison With Experimentsmentioning

confidence: 82%

“…Note that all directions are given in degrees true north (measured clockwise from the north). For more information on the experiment and the ground data the reader is referred to Hennings et al (1998 ).…”

Section: Methodsmentioning

confidence: 99%

“…Hennings (1984 ), Shuchmann et al (1985 ), Holliday et al (1986), Vogelzang (1989Vogelzang ( , 1997, Hennings (1991), Cooper et al (1994), Van der Kooij et al (1995), and Hennings et al (1998 ).…”

Section: Modelmentioning

confidence: 95%

“…The wind speed was 9 m sÕ 1 during recording of the radar images. Hennings et al (1998) give an overview of available ground truth data and the images. In particular, depth and surface ow maps of the area are available.…”

Section: Introductionmentioning

confidence: 99%

“…Swell was removed by ltering while wind streaks and turbulence, most clearly visible at C-and X-bands, were removed by averaging over 50 or 100 images lines. The reader is referred to Hennings et al (1998 ) for more details.…”

Section: Introductionmentioning

confidence: 99%

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A model comparison study to the imaging of submarine reefs with synthetic aperture radar

Vogelzang¹

2001

International Journal of Remote Sensing

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Signatures of submarine reefs near Heligoland in the North Sea were observed in airborne radar images recorded at L-, C-and X-bands on 14 November 1990 during rather high wind speed of 9 m sÕ 1. Predictions from various models of the imaging mechanism were compared to these observations. One of the models is the so-called weak hydrodynamic interaction theory (WHIT) model. It is fully two-dimensional in position as well as wavenumber space, so any surface current variation can be handled. Also more sophisticated scattering models than rst-order Bragg scattering can be included. The model contains a number of parameterizations for the roughness length, the equilibrium wave height spectrum and the relaxation rate as well as diVerent forms for the local relaxation source term. In the model intercomparison, the WHIT model performed not very well. It is shown here that this is due to the choice of the radial relaxation rate. In a sensitivity analysis it is shown that also the form of the relaxation source term is important. A linear source term may lead to unrealistically high positive hydrodynamic modulations (up to 50 dB) at some positions over the reefs for waves with a wavelength of about 0.6 m. Such eVects do not occur in quadratic or cubic source terms, which are therefore to be preferred. The parameterizations chosen for the roughness length and the angular relaxation rate have little in uence on the model results. Also shoaling may be neglected. A scattering model based on rst iteration of the Stratton-Chu equation gives results similar to that of an improved two-scale model. When compared to the observations, good agreement is obtained at L-band, but at C-and X-bands the model underestimates the modulations. A number of possible causes is discussed, but additional data are needed to settle this question.

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Section: Comparison With Experimentsmentioning

confidence: 82%

Section: Methodsmentioning

confidence: 99%