Radar Scattering from Modulated Wind Waves

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März 1989



Ten years ago, de Loor and co-workers at TNO, The Netherlands, were the first to report bottom topography patterns in real aperture radar (RAR) images of the southern North Sea. At that time, this was a real puzzle. The skin depth of microwaves for sea water is only of the order of centimeters while the sea bottom is about 20 meters below the surface. Electromagnetic radiation therefore cannot probe the bottom directly. Similar phenomena were found in radar imagery from SEASAT and SIR-AlB synthetic aperture radars (SAR's) of Nantucket Shoals, the English Channel and many other coastal areas. Since then theory and ocean field experiments (Le., Phelps Bank, Georgia Straits, SARSEX, TOWARD, FASINEX, etc.) have advanced our understanding considerably. We now know that these surface signatures are the results of surface currents, perturbed by the bottom topography, which refract the propagation and modulate the energy of (short) surface waves so as to cause microwave backscatter power variations. Hence, any large scale ocean features containing nonuniform surface currents (i.e. internal waves, eddies, fronts, etc.) will cause similar manifestations in the radar imagery by means of current-wave-microwave interactions. Observations confirm this.


Session 1 Tidal Currents and Bathymetry.- Determining the currents over Phelps Bank.- Studies of the sea surface with radar in the Netherlands.- Session 2 Electromagnetic Scattering.- Calculation of microwave Doppler spectra from the ocean surface with a time-dependent composite model.- Limitations of the two-scale theory for microwave backscatter from the ocean.- First results of the VIERS-1 experiment.- Session 3 The Energy Balance in Short Waves.- Effects of reduced surface tension on short waves at low wind speeds in a fresh water lake.- The energy balance in short gravity waves.- Derivation of Phillips a parameter from turbulent diffusion as a damping mechanism.- Temporal and spatial variability of the wind stress vector.- Energy balance in small scale waves - An experimental approach using optical slope measuring technique and image processing.- On the changes in phase speed of one train of water waves in the presence of another.- Session 4 Perturbation of the Gravity-Capillary Wave Spectrum by Current Variation.- SAR imaging of ocean waves in the presence of variable currents.- The Modulation Transfer Function: concept and applications.- Measurement of short wave modulation by long waves using stereophotography and a laser-slope sensor in TOWARD.- The surface signatures of internal waves in the ocean: Introduction and systematics.- The surface signatures of internal waves in the ocean: Some particular cases.- Short wave modulation and breaking, experimental results.- Nonlinearity as the missing link between wavelets and currents.- The trickle down of wave modulations from swell to gravity-capillary waves.- The mapping of underwater bottom topography with SLAR.- Session 5 General Discussion.- General discussion on electromagnetic scattering.- General discussion on the energy balance in short wind waves.- General discussion on perturbation of the gravity-capillary wave spectrum by current variations.- Author index.- List of participants.


EAN: 9780792301462
ISBN: 0792301463
Untertitel: Proceedings of the Workshop on Modulation of Short Wind Waves in the Gravity-Capillary Range by Non-Uniform Currents, held in Bergen aan Zee, The Netherlands, 24-26 May 1988. 1989. Auflage. Book. Sprache: Englisch.
Verlag: Springer
Erscheinungsdatum: März 1989
Seitenanzahl: 288 Seiten
Format: gebunden
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