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ABSTRACT: Wave tank experiments were performed to study features of microwave radar backscattering by strongly nonlinear gravity-capillary
waves (GCWs). Backscattering by centimeter and partly decimeter GCW was found to be related to the microbreaking of GCWs and
the generation of parasitic capillary ripples. The scattering of meter-scale GCWs was attributed to the effects of strong
breaking, i.e., to the overturning of wave crests and the excitation of quasilinear (free) capillary ripples, while the scatterers
for intermediate decimeter GCWs were both free and parasitic ripples.
Bulletin of the Russian Academy of Sciences Physics 04/2012; 74(12):1695-1698.
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ABSTRACT: The mechanism of the resonance (Bragg) scattering of microwaves by gravity-capillary waves (GCWs) is checked experimentally.
Resonant regularities of backscattered signal intensity are obtained as functions of frequency and GCW propagation direction.
It is shown that the width of the resonance curves is determined by the width of the directivity pattern of the scatterometer’s
antenna. The excitation of the GCW second harmonic and the spatial structure of the wave field at the GCW doubled frequency
are investigated. The ratio of the amplitudes of the free wave and forced harmonic that originated during excitation of the
primary wave is determined. The resonance curve is obtained for the second-order scattering of radio waves (on forced harmonics
and free GCWs). The correction to the backscattering cross section is investigated in the second order of smallness relative
to the Bragg term.
Izvestiya Atmospheric and Oceanic Physics 03/2007; 43(2):243-249. · 0.44 Impact Factor
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ABSTRACT: New effects recently revealed in field experiments conducted in IAP RAS on radar probing of the sea surface and associated with strong nonlinearity of short gravity-capillary waves and generation of high-order harmonics and "parasitic" capillary ripples (bound waves) are discussed. Wave tank experiments on radar probing of short wind waves in the presence/ absence of films are also described and relative intensities of linear and bound waves are estimated. Field and wave tank experiments has confirmed the expected intensification of modulation of Bragg ripples due to long surface waves, the modulation coefficient has been shown to be several times the modulation on a clean water surface.
OCEANS 2003. Proceedings; 10/2003
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ABSTRACT: Doppler shifts of Ka-band radar signals backscattered by short wind waves in the presence of organic films have been studied in wave tank experiment at low wind speeds and at different surfactant concentrations. It is shown that phase velocities of mm-scale wind ripples, retrieved from radar Doppler shifts, do not obey the linear dispersion relationship and are determined by the velocities of free gravity-capillary waves and of bound waves - nonlinear harmonics of decimetre-scale dominant waves. A relative intensity of the bound waves as a function of surfactant concentration is estimated. Damping of free and bound waves due to surfactant films has been analysed theoretically and a qualitative explanation of changing of radar Doppler shifts in the presence of films is given.
Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 07/2002
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ABSTRACT: Results of field experiments on remote sensing of organic slicks on the sea surface using Ka-band radar are presented. Slicks of different surfactants with the film elasticity values ranging from some mN/m to some tens of mN/m were studied. It is shown that the radar Doppler shifts can change strongly in slicks, depending on the film elasticity, while the depression of radar backscatter in slicks is nearly the same for the different substances. A physical explanation of the effect is given assuming different contributions of free capillary-gravity waves and "bound waves" - nonlinear harmonics of longer surface waves in the spectrum of cm- to mm-scale wind waves. A simple theory of wave damping in slicks is used to explain qualitatively the dependence of the Doppler shifts on film elasticity.
Geoscience and Remote Sensing Symposium, 2002. IGARSS '02. 2002 IEEE International; 02/2002
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ABSTRACT: Modulation of radar backscatter due to long wind waves in the presence of surfactant films is studied for the first time under wave-tank conditions. It is found that the modulation coefficient can increase significantly with increasing surfactant concentration. We show that the existing theoretical models of modulation of free surface waves underestimate the observed modulation levels. It is demonstrated that the experimental radar Doppler shifts cannot be explained by only the scattering due to free gravity-capillary waves (GCW) and are also determined by coupled waves, which are nonlinear harmonics of the longer wind wave components. Estimates of the relative intensity of coupled waves in the wind-wave spectrum at the Bragg wavelength are presented. It is shown that the contribution of coupled waves is considerable and increases with increasing surfactant concentration, thus confirming the hypothesis for a cascade mechanism of strong backscatter modulation in the long-wave field.
Radiophysics and Quantum Electronics 01/2002; 45(12):942-957. · 0.71 Impact Factor
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ABSTRACT: Modulation of radar backscatter due to long wind waves for Ka-band radar has been studied in wave tank experiments at different wind velocities and fetches. The modulation transfer function (MTF) was analysed, and it is shown that the mechanisms of tilt modulation, hydrodynamic straining and modulation of wind stress strongly underestimate the effect when compared with experiment. Radar Doppler shifts were measured and they were shown to be larger than those, connected with free gravity-capillary Bragg waves, and smaller than for bound waves, generated by decimetre-scale dominant wind waves and propagating with their phase velocities. It is shown that the contribution of the bound waves in the short wind-wave spectrum, estimated from the measured Doppler shifts is significant so that these waves can give strong modulation of radar backscatter
Geoscience and Remote Sensing Symposium, 2001. IGARSS '01. IEEE 2001 International; 02/2001
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ABSTRACT: A new mechanism of strong (“cascade”) modulation of
capillary-gravity waves (CGW) under the action of internal waves was
studied in wave tank experiments. The mechanism is connected with
so-called bound CGW, which are nonlinear high-order harmonics of short
gravity waves (SGW). The simple case of centimetre-millimetre-(cm-mm-)
scale bound waves, generated by periodic decimetre-(dm-)scale SGW was
investigated. The modulation coefficient of the bound harmonics
including “parasitic” capillary ripples generated by SGW has
been estimated. It is obtained that the modulation coefficient of bound
CGW depends on the steepness of basic SGW and can be almost an order of
magnitude larger than the modulation coefficient of SGW
Geoscience and Remote Sensing Symposium, 2000. Proceedings. IGARSS 2000. IEEE 2000 International; 02/2000
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ABSTRACT: An optical model of imaging of film slicks on the sea surface in scattered sky light is discussed. Experimental verification of the model is presented based on measurements of the sky radiance profiles and of wave damping in the spectrum of short wind waves due to organic films. The measurements were carried out in field experiments with artificial slicks using optical spectrum analysers and photometers at different sea states and geometry of observations. Simultaneously measured wavenumber spectra, the spectrum contrasts in slicks, and the sky light angular distributions are presented. Using a simple model of wind wave damping due to films and the optical model of wave imaging, variations of the sea surface radiance in slicks are calculated and are shown to be in good agreement with experiment. Possibilities of slick detection by simple optical instruments under different observational conditions are discussed
Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International; 02/1999
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ABSTRACT: Presents new extended measurements of wind waves in the presence
of artificial organic films, using two optical spectrum analysers, one
measuring phase velocities and the other measuring variations of the
wavenumber spectrum of the wind waves. It has been found that, in the
presence of films, the observed phase velocities are closer to those of
free linear gravity-capillary waves than they are in the case of clean
water. This can be explained by the bound waves being more strongly
damped than the free waves. The relation between bound and free waves is
estimated from measurements of phase velocity. Wind ripple damping has
been found to be maximum at wavelengths around 5-7 mm. This is in
agreement with the predictions of the new mechanism, and it also agrees
with field experiments using artificial slicks
Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International; 02/1999
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ABSTRACT: New observations are presented of natural banded slicks and their
associated internal waves (IW), conducted from an oceanographic platform
on the Black Sea in June, 1998. Surface waves were measured with X-band
and Ka-band radars and with an optical spectrum analyzer operating in
the cm and mm surface wavelength ranges; IW were measured with an
STD-probe. Surface films were sampled in both slick and non-slick areas,
and the film elasticity parameter and film concentration variations were
estimated from these samples using laboratory measurements of
capillary-gravity wave damping. The estimated film elasticities for the
slick bands exceeded 20 mN/m, while those in non-slick areas were only a
few mN/m. The most prominent slick bands were detected over IW troughs,
in accordance with theory. The relative cm-mm-scale wave damping
(contrast) in the slick bands was very high (more than an order of
magnitude), reaching a maximum for wavelengths ~1.5 cm. Comparison of
observed wave damping in the banded slicks with hydrodynamic modulation
over IW in nonslick cases has shown that the presence of surfactants
strongly enhances the surface manifestation of the IW
Geoscience and Remote Sensing Symposium, 1999. IGARSS '99 Proceedings. IEEE 1999 International; 02/1999
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ABSTRACT: Field experiments involving artificial slicks of different
surface-active substances were carried out from an oceanographic
platform on the Black Sea in September, 1997. Simultaneous measurements
were made of the wavenumber-frequency spectrum of
centimetre(cm)/millimetre(mm)-scale wind waves and of radar backscatter,
using optical spectrum analysers and a coherent Ka-band radar operating
at incidence angles about 60°. Phase velocities of wind waves were
retrieved from measurements of the Doppler shifts of the radar and
optical analyser signals. It was found that the suppression of
cm-mm-scale wind waves in slicks is accompanied by an increase in the
average microwave Doppler shifts and, consequently, in the mean phase
velocities of the short wind waves. The increase of phase velocity in
slicks can be explained by the influence of bound harmonics of the
decimetric waves which are assumed to dominate the spectrum of
cm-mm-scale waves in slicks. Another reason for the increase in Doppler
shifts is the strong modulation of short wind waves in slicks due to
long wind waves
Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International; 08/1998
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ABSTRACT: Wave tank studies of wind waves were carried out using an optical
spectrum analyser and an artificial gradient illuminator. The
wavenumber-frequency spectrum and phase velocities of gravity-capillary
waves were measured over the wavelength range from about 10 cm to 6 mm.
It was found that the phase velocities for wavelengths smaller than 2-3
cm remain nearly constant and do not follow the dispersion relation of
free surface waves. These phase velocities were found to increase with
fetch, in the way that the wave phase velocity of the dominant
decimetric wind waves increases with fetch. One thus can conclude that
the wind wave spectrum contains nonlinear cm-mm-scale harmonics that are
bound to the dominant wind waves, propagating with the phase velocities
of the decimetric waves
Geoscience and Remote Sensing Symposium Proceedings, 1998. IGARSS '98. 1998 IEEE International; 08/1998
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ABSTRACT: Damping of short centimetre-millimetre (cm-mm)-scale wind waves
was studied during experiments conducted from a platform in the Black
Sea. During the experiments artificial organic slicks were observed
using Ka-band and X-band radars and using optical spectrum analysers.
Film sampling from the artificial slicks with small nylon nets was also
performed and the film elasticity was later estimated from laboratory
measurements of wave damping. One of the experiments was conducted
during an ERS-2 satellite overpass and the slick was imaged by the
C-band ERS-2 SAR. It is shown that damping of mm-scale waves exceeds the
damping of cm-dm-waves and exhibits a maximum at surface wavelengths
about 5-7 mm. The maximum is assumed to be a manifestation of a new
nonlinear mechanism of damping of “parasitic” capillary
ripples generated on the slopes of decimetre (dm)-scale wind waves
Geoscience and Remote Sensing, 1997. IGARSS '97. Remote Sensing - A Scientific Vision for Sustainable Development., 1997 IEEE International; 09/1997
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ABSTRACT: Doppler spectra obtained using an X-band radar have been used to
study artificial slicks. The radar was deployed on a platform in the
Black Sea to image slicks which were artificially laid in the sea
nearby. The radar viewed the slicks at about an angle of 20°
incidence. The Doppler spectra obtained from slick covered regions
showed strong shifts of the mean Doppler return towards higher
frequencies compared with that obtained from non-slick areas. The change
in Doppler spectra can be explained if the relative contributions to the
radar backscatter from Bragg and specular scatterers changes in the
slick covered areas compared with that in non-slick areas. The
experimental results are found to be in good agreement with theoretical
predictions
Geoscience and Remote Sensing, 1997. IGARSS '97. Remote Sensing - A Scientific Vision for Sustainable Development., 1997 IEEE International; 09/1997
