Papers by Francis Felizardo
Journal of Physical Oceanography, Apr 1, 1995
Journal of the Acoustical Society of America, Apr 1, 1993
Ambient Surface Noise and Ocean Surface Waves
Measurements of the ambient noise spectrum level N with simultaneous, coincident wind and wave me... more Measurements of the ambient noise spectrum level N with simultaneous, coincident wind and wave measurements were made from RP Flip in Fall 1991. The measurements were designed to investigate the correlation between the ambient noise and surface wave parameters. The results suggest that wave parameters related to the incidence of wave breaking correlate well with the ambient noise level. The correlation between N and the RMS wave amplitude a was found to be poor but that between N and the RMS amplitude of the local wind sea aw was comparable to that between wind speed U and N. Similar good correlations were found between the RMS wave slope s and N, and the higher frequency surface wave spectral levels and N. Correlations between the surface wave dissipation estimates D based on the Hasselmann (1974) and Phillips (1985) models and the ambient noise were comparable to those between the wind speed and N. The mean square acoustic pressure was found to be proportional to D with n in the range 0.6 0.8. The implications of these results for monitoring surface waves and air-sea fluxes are discussed.
Ambient Surface Noise and Ocean Surface Waves
Sea Surface Sound '94, 1996
Measurements of the ambient noise spectrum level N with simultaneous, coincident wind and wave me... more Measurements of the ambient noise spectrum level N with simultaneous, coincident wind and wave measurements were made from RP Flip in Fall 1991. The measurements were designed to investigate the correlation between the ambient noise and surface wave parameters. The results suggest that wave parameters related to the incidence of wave breaking correlate well with the ambient noise level. The correlation between N and the RMS wave amplitude a was found to be poor but that between N and the RMS amplitude of the local wind sea aw was comparable to that between wind speed U and N. Similar good correlations were found between the RMS wave slope s and N, and the higher frequency surface wave spectral levels and N. Correlations between the surface wave dissipation estimates D based on the Hasselmann (1974) and Phillips (1985) models and the ambient noise were comparable to those between the wind speed and N. The mean square acoustic pressure was found to be proportional to D with n in the range 0.6 0.8. The implications of these results for monitoring surface waves and air-sea fluxes are discussed.
There is a growing consensus that the sound generated by breaking waves is responsible for much o... more There is a growing consensus that the sound generated by breaking waves is responsible for much of the ambient noise level in the ocean. While numerous field measurements have shown a strong correlation between the ambient noise spectrum level (N) in the range 100Hz to 25kHz and wind speed in the ocean, very little has been done to establish a comparable correlation between the ambient noise spectrum level and surface wave field parameters. The difficulty in establishing this relationship is remarkable given that the frequency and intensity of wave breaking are dependent on the characteristics of the wave field. In Fall1991, an experiment was conducted from the research platform Flip 130 kilometers off the coast of Oregon, where the ambient noise between 2.5 and 25 kHz, the wind speed, and the sea surface elevation using wire wave gauges were measured. The correlation between Nand the root mean square wave amplitude a was found to be poor but could be improved if the swell was filtered out from the wave elevation time series. The influence of swell on the value of a was disproportionate to the level of ambient noise since its characteristics were not directly due to the local wind-wave conditions. Observations of the dependence of the high frequency wind waves and the directional wave spectrum under turning winds suggested that the high frequency wave components responded more quickly to changes in the wind speed and wind direction than the energy-containing frequencies. The ambient noise level also correlated well with the root mean square wave slopes. This is consistent with previous laboratory measurements which showed that the steepness of a packet of waves correlates with the strength of wave breaking and with characteristics of breaking waves such as loss of momentum flux, dissipation, initial volume of air entrained, mixing, and sound generation. Comparisons of surface wave dissipation estimates using field measurements and models developed by Phillips {1985) and Hasselmann {1974) show that although the two models have very different forms, they give values that are comparable in magnitude. The relationship between the ambient noise level and log of dissipation give correlation coefficients (0.93-0.95) that are comparable to those between ambient noise and wind speed. The mean square acoustic pressure was shown to vary with the dissipation, with p2 oc D0.6-0.8. The results suggest that measurements of ambient sound may prove to be useful in inferring surface wave dissipation.
The Journal of the Acoustical Society of America, 1993
An experiment that measured the NSL between 2 to 25 kHz, the wind speed U, and the directional wa... more An experiment that measured the NSL between 2 to 25 kHz, the wind speed U, and the directional wave spectrum was conducted off the coast of Oregon to examine the correlation between the ambient noise spectrum level (NSL) and surface wave parameters. These measurements show that although the correlation between the ambient NSL and the rms wave height is poor, the NSL and wave height spectrum energy levels at frequencies somewhat higher than the spectral peak give correlation coefficients that are comparable to that between the well-known correlation between U and NSL. Estimates of wave energy dissipation due to breaking waves using models proposed by Komen et al. [J. Phys. Ocean. 14, 1271–1285 (1984)] and Phillips [J. Fluid Mech. 156, 505–531 (1985)] likewise give comparable correlation coefficients. These results are consistent with the laboratory experiments [M. R. Loewen and W. K. Melville, J. Fluid Mech. 224, 601–623 (1991)] which show that the energy dissipated by wave breaking ...
Journal of Physical Oceanography, 1995
Journal of Geophysical Research, 2004
We present measurements of Ku band electromagnetic (EM) bias made for 2 months from a platform in... more We present measurements of Ku band electromagnetic (EM) bias made for 2 months from a platform in Bass Strait off the southeast coast of Australia during the austral winter of 1992. EM bias, , the difference between the electromagnetic and true mean sea levels, was measured using Doppler scatterometers. Linear wave theory was used to relate the Doppler signal to the surface displacement, giving simultaneous coincident backscatter and wave measurements, including significant wave height, H s . On the basis of dimensional reasoning, we suggest that the usual inhomogeneous correlations of the normalized bias b = /H s with the 10 m wind speed, U 10 , and H s may be improved by correlating the data with nondimensional variables, including a characteristic wave slope, s, and wave age, c/U 10 , where c is a characteristic phase speed of the surface waves. Using both polynomial correlations and optimal estimation techniques to fit the data, we find that the standard error of the fit is reduced by $50% when the dimensionless variables are used. We find that the dependence of the EM bias on the wave slope is consistent with earlier tower-based measurements and the theory of short-wave modulation by longer waves. We discuss the implications of these results for operational implementation of EM bias algorithms based on wave slope and wave age.
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Papers by Francis Felizardo