913 research outputs found
Semiclassical and spectral analysis of oceanic waves
In this work we prove that the shallow water flow, subject to strong wind
forcing and linearized around an adequate stationary profile, develops for
large times closed trajectories due to the propagation of Rossby waves, while
Poincar\'e waves are shown to disperse. The methods used in this paper involve
semi-classical analysis and dynamical systems for the study of Rossby waves,
while some refined spectral analysis is required for the study of Poincar\'e
waves, due to the large time scale involved which is of diffractive type
On the propagation of oceanic waves driven by a strong macroscopic flow
In this work we study oceanic waves in a shallow water flow subject to strong
wind forcing and rotation, and linearized around a inhomogeneous (non zonal)
stationary profile. This extends the study \cite{CGPS}, where the profile was
assumed to be zonal only and where explicit calculations were made possible due
to the 1D setting. Here the diagonalization of the system, which allows to
identify Rossby and Poincar\'e waves, is proved by an abstract semi-classical
approach. The dispersion of Poincar\'e waves is also obtained by a more
abstract and more robust method using Mourre estimates. Only some partial
results however are obtained concerning the Rossby propagation, as the two
dimensional setting complicates very much the study of the dynamical system
Variational Stereo Imaging of Oceanic Waves with Statistical Constraints
An image processing observational technique for the stereoscopic reconstruction of the wave form of oceanic sea states is developed. The technique incorporates the enforcement of any given statistical wave law modeling the quasi Gaussianity of oceanic waves observed in nature. The problem is posed in a variational optimization framework, where the desired wave form is obtained as the minimizer of a cost functional that combines image observations, smoothness priors and a weak statistical constraint. The minimizer is obtained combining gradient descent and multigrid methods on the necessary optimality equations of the cost functional. Robust photometric error criteria and a spatial intensity compensation model are also developed to improve the performance of the presented image matching strategy. The weak statistical constraint is thoroughly evaluated in combination with other elements presented to reconstruct and enforce constraints on experimental stereo data, demonstrating the improvement in the estimation of the observed ocean surface
Weak Statistical Constraints for Variational Stereo Imaging of Oceanic Waves
We develop an observational technique for the stereoscopic reconstruction of the wave form of oceanic sea states via a variational stereo method. In the context of active surfaces, the shape and radiance of the wave surface are obtained as minimizers of an energy functional that combines image observations and smoothness priors. To obey the quasi Gaussianity of oceanic waves observed in nature, a given statistical wave law is enforced in the stereo variational framework as a weak constraint. Multigrid methods are then used to solve the partial differential equations derived from the optimality conditions of the augmented energy functional. An application of the developed method to two sets of experimental stereo data is finally presented
Oceanic wave measurement system
An oceanic wave measured system is disclosed wherein wave height is sensed by a barometer mounted on a buoy. The distance between the trough and crest of a wave is monitored by sequentially detecting positive and negative peaks of the output of the barometer and by combining (adding) each set of two successive half cycle peaks. The timing of this measurement is achieved by detecting the period of a half cycle of wave motion
Cosmic signatures in earth's seismic tremor?
Even in absence of earthquakes, each site on earth experiences continuous
elastic vibrations which are mostly traced to the non-linear interactions of
sea waves. However, the fine structure of the spectrum at mHz frequencies shows
hundreds of highly significant narrow bandwidth peaks, with a persistence and a
coincidence with solar acoustic eigenmodes which are incompatible with any
geophysical origin. The feasibility of a common cosmic origin is evaluated
through an estimate of the gravitational wave cross-section of the earth,
combined with its elastic response and with the stochastic amplification
produced by the interference of the cosmic signal with tremor of oceanic
origin. The measured spectral peaks appear compatible with a gravitational
monochromatic illumination at strains . We analize in
detail the band around 2.614 mHz, where the binary white dwarf J0651+2844 -
which is the second strongest known gravitational stellar source - is expected
to emit. Compatible spectral tremor peaks are found for both the earth and the
sun, but their amplitude is 3 o.m. larger than independent estimates, so that a
gravitational source attribution would call for a variety of unknown
non-luminous sources with definite mass-distance ratios
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