7,724 research outputs found
Geodetic satellite altimeter study - A review of electromagnetic scattering from the ocean surface
Electromagnetic wave scattering by sea surfaces relevant to geodetic satellite altimeter desig
Current effects on scattering of surface gravity waves by bottom topography
Scattering of random surface gravity waves by small amplitude topography in
the presence of a uniform current is investigated theoretically. This problem
is relevant to ocean waves propagation on shallow continental shelves where
tidal currents are often significant. A perturbation expansion of the wave
action to second order in powers of the bottom amplitude yields an evolution
equation for the wave action spectrum. A scattering source term gives the rate
of exchange of the wave action spectrum between wave components, with
conservation of the total action at each absolute frequency. With and without
current, the scattering term yields reflection coefficients for the amplitudes
of waves that converge, to the results of previous theories for monochromatic
waves propagating in one dimension over sinusoidal bars. Over sandy continental
shelves, tidal currents are known to generate sandwaves with scales comparable
to those of surface waves. Application of the theory to such a real topography
suggests that scattering mainly results in a broadening of the directional wave
spectrum, due to forward scattering, while the back-scattering is generally
weaker. The current may strongly influence surface gravity wave scattering by
selecting different bottom scales with widely different spectral densities due
the sharp bottom spectrum roll-off.Comment: submitted to Journal of Fluid Mechanics 7 Oct 200
Toward RADSCAT measurements over the sea and their interpretation
Investigations into several areas which are essential to the execution and interpretation of suborbital observations by composite radiometer - scatterometer sensor (RADSCAT) are reported. Experiments and theory were developed to demonstrate the remote anemometric capability of the sensor over the sea through various weather conditions. It is shown that weather situations found in extra tropical cyclones are useful for demonstrating the all weather capability of the composite sensor. The large scale fluctuations of the wind over the sea dictate the observational coverage required to correlate measurements with the mean surface wind speed. Various theoretical investigations were performed to establish a premise for the joint interpretation of the experiment data. The effects of clouds and rains on downward radiometric observations over the sea were computed. A method of predicting atmospheric attenuation from joint observations is developed. In other theoretical efforts, the emission and scattering characteristics of the sea were derived. Composite surface theories with coherent and noncoherent assumptions were employed
The composite scattering model for radar sea return
A composite scattering model, suitable for explaining the behavior of measured scattering cross sections of the ocean surface, is presented. Furthermore, utilizing this scattering model, the spectrums of the small gravity, gravity-capillary, waves will be predicted for MSA/MSC, 13.3 GHz Scatterometer data
Wave modelling - the state of the art
This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered.
The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments
Visualizing characteristics of ocean data collected during the Shuttle Imaging Radar-B experiment
Topographic measurements of sea surface elevation collected by the Surface Contour Radar (SCR) during NASA's Shuttle Imaging Radar (SIR-B) experiment are plotted as three dimensional surface plots to observe wave height variance along the track of a P-3 aircraft. Ocean wave spectra were computed from rotating altimeter measurements acquired by the Radar Ocean Wave Spectrometer (ROWS). Fourier power spectra computed from SIR-B synthetic aperture radar (SAR) images of the ocean are compared to ROWS surface wave spectra. Fourier inversion of SAR spectra, after subtraction of spectral noise and modeling of wave height modulation, yields topography similar to direct measurements made by SCR. Visual perspectives on the SCR and SAR ocean data are compared. Threshold distinctions between surface elevation and texture modulations of SAR data are considered within the context of a dynamic statistical model of rough surface scattering. The result of these endeavors is insight as to the physical mechanism governing the imaging of ocean waves with SAR
Microwave backscattering theory and active remote sensing of the ocean surface
The status is reviewed of electromagnetic scattering theory relative to the interpretation of microwave remote sensing data acquired from spaceborne platforms over the ocean surface. Particular emphasis is given to the assumptions which are either implicit or explicit in the theory. The multiple scale scattering theory developed during this investigation is extended to non-Gaussian surface statistics. It is shown that the important statistic for the case is the probability density function of the small scale heights conditioned on the large scale slopes; this dependence may explain the anisotropic scattering measurements recently obtained with the AAFE Radscat. It is noted that present surface measurements are inadequate to verify or reject the existing scattering theories. Surface measurements are recommended for qualifying sensor data from radar altimeters and scatterometers. Additional scattering investigations are suggested for imaging type radars employing synthetically generated apertures
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