IEEE Journal of Oceanic Engineering

Ambient noise in the surf zone, in the frequency range 120 Hz to 5 kHz, was recorded using a broad-band hydrophone, located approximately 1 m above bottom and 1-2 m below the mean sea surface. The predominant source of this noise is breaking waves. Analysis of simultaneous land-based video observations of the sea surface in the region of the hydrophone, along with wave height data, reveals quantit... View full abstract»

Experiments using seismic-type arrays with lengths in terms of wavelengths λ, from 20λ at 50 Hz to 143λ at 340 Hz have been conducted in the Mediterranean Sea and Northwest Atlantic Basin to ranges of 750 km. Signal-gain cumulative distribution functions (CDFs) were experimentally determined as a function of acoustic aperture and integration time. We found that for an array 14... View full abstract»

An efficient and robust method has been developed to locate multiple impulsive sources in an ocean environment. Global position system (GPS) receivers were installed on sonobuoys to obtain their locations within a few meters of accuracy. A sonobuoy field was deployed in a ring-type pattern. Charges were then set off at arbitrary locations within the ring, High-resolution plots were used to obtain ... View full abstract»

The concept of modeforming with a vertical line array for active target detection in a reverberation-limited shallow-water environment is explored. The concept is based on the hypothesis that, in certain environments, the reverberation field is due to subbottom scattering and the reverberant energy is carried by the higher order modes; on the other hand, the targets in the water column are contain... View full abstract»

Conventional methods for modal beamforming of underwater acoustic signals using a vertical-line hydrophone array (VLA) can suffer significant degradation in resolution when the array is geometrically deficient, i.e., consists of sparsely spaced elements and spans the water column partially or is poorly navigated. Designed for estimating the coefficients of the normal modes, these conventional meth... View full abstract»

In a shallow-water ocean environment, the range dependent variation of the geoacoustic properties of the seabed is one of the crucial factors affecting sound propagation. Since the local modes of propagation depend on the spatial changes in the bottom sediments, the local eigenvalues of these modes are useful as tools for examining the range dependence of the sediment properties. In order to extra... View full abstract»

This paper introduces a novel ESPRIT-based closed form source localization algorithm applicable to arbitrarily spaced three-dimensional arrays of vector hydrophones, whose locations need not be known. Each vector hydrophone consists of two or three identical but orthogonally oriented velocity hydrophones plus one pressure hydrophone, all spatially co-located in a point-like geometry. A velocity hy... View full abstract»

Determinations of acoustic scattering strength for sand bottoms have been made at several different shallow-water areas under downward refracting sound propagation conditions in the frequency decade below 1 kHz. The measurements have been made using explosive sources detonated at mid-water depth and bottom-mounted vertical and horizontal hydrophone line arrays as receivers. The ubiquitous presence... View full abstract»

Ambient noise measurements made in Monterey Bay, CA, in 1981 were reduced by estimations of wave-breaking noise and the residual noise was combined with modeled transmission loss (TL) to estimate the spectral source level of surf-generated noise. A Hamilton geoacoustic model of the coastal environment was derived and used in a finite-element parabolic equation propagation-loss model to obtain TL v... View full abstract»

For pt.I see ibid., vol.22, no.3, p.425-33 (1997). Ambient noise measurements collected off the coast of Duck, NC, were used in conjunction with modeled transmission loss (TL) and estimated ambient noise due to wave-breaking to generate estimates of spectral source level densities (per meter of surf zone) of surf-generated ambient noise. Estimates of both continuous (local) and discrete (distant) ... View full abstract»

High-frequency (120 and 420 kHz) sound was used to survey sound scatterers in the water over Georges Bank. In addition to the biological sound scatterers (the plankton and micronekton), scattering associated with internal waves and suspended sediment was observed. Volume backscattering was more homogeneous in the vertical dimension (with occasional patches) in the shallow central portion of the Ba... View full abstract»

An overview is given of the July-August 1995 SWARM shallow-water internal wave acoustic scattering experiment. This experiment studied both acoustic propagation through and scattering by the linear and nonlinear internal waves found on the Mid-Atlantic Bight continental shelf, as well as the physical oceanography of the internal wavefield. In order that their goal of explaining the nature of the a... View full abstract»