An assessment of fuzzy logic vessel path control

This paper presents a method of determining the compressional wave attenuation in marine sediment from a short range measurement. The data were collected on a vertical line array at a range of 230 m during the Shallow Water 2006 experiments. The sediment attenuation is extracted from the signal strength ratio of the sea bottom reflection to a sub-bottom reflection at different frequencies from 1.75 to 3.15 kHz. Linear frequency dependence of the attenuation is found from the estimation. The sediment attenuation estimate is lower than the values estimated from the inversions of acoustic field data previously done in the vicinity.

Section: Resultsmentioning

confidence: 87%

Estimating marine sediment attenuation at low frequency with a vertical line array

Jiang

Chapman

Yang

et al. 2009

“…Due to this fact, the horizontal wave number spectrum contains information about the geoacoustic properties in the bottom. Methods for evaluating the Hankel transform include evaluation of the asymptotic form by fast Fourier transform, 1,4 . Filon quadrature, 10 and trapezoidal rule quadrature integration, 10 which we use in this analysis.…”

Section: Resultsmentioning

confidence: 99%

“…The measurement of the complex pressure to a 5 km range took up to 8 h, over which the tides and currents were changing the character and depth of the water column. Carey et al 4 extended this technique, by the use of a vertical array and a moving source emitting four frequencies, and showed that coherent processing of frequencies up to 275 Hz covering ranges of 4 km over a 2 h period were possible. Motivated by the quality of results obtained using the synthetic aperture technique and inspired by current autonomous underwater vehicle ͑AUV͒ technology, an effort was initiated to determine if a synthetic aperture measurement could be cost-effectively and efficiently performed using a single ship and an AUV with a towed array.…”

Section: Introductionmentioning

confidence: 99%

Results from an autonomous underwater vehicle towed hydrophone array experiment in Nantucket Sound

Holmes

Carey

Lynch

2006

Shallow water experiments have been conducted in Nantucket Sound with an autonomous underwater vehicle towed hydrophone array system in an area proximate to that of a previous experiment [Frisk and Lynch, J. Acoust. Soc. Am. 86, 1928–1939 (1989)]. Transmission loss was measured, for frequencies between 220 and 1228Hz in an ocean waveguide, under conditions of an isovelocity water column with an approximate depth of 13m over a sandy-silty bottom. Results obtained at 415Hz show classic isovelocity waveguide phenomena that include interference effects, mode stripping due to modal attenuation, and transmission loss proportional 15 to 10log10(R).

“…Resonant modes are characterized by mode functions which are strongly amplified within a layer. [38][39][40] This effect is illustrated by mode shapes calculated at 200 Hz for a single point in the x-y plane (corresponding to 73.02 W, 39.01 N-the approximate location of the Shark VLA) shown by the solid lines in Fig. 7.…”

Section: A Modal Amplitudementioning

confidence: 99%

Horizontal refraction of propagating sound due to seafloor scours over a range-dependent layered bottom on the New Jersey shelf

Ballard

Lin

Lynch

2012

Three-dimensional propagation effects of low frequency sound from 100 to 400 Hz caused by seafloor topography and range-dependent bottom structure over a 20 km range along the New Jersey shelf are investigated using a hybrid modeling approach. Normal modes are used in the vertical dimension, and a parabolic-equation approximate model is applied to solve the horizontal refraction equation. Examination of modal amplitudes demonstrates the effect of environmental range dependence on modes trapped in the water column, modes interacting with the bottom, and modes trapped in the bottom. Using normal mode ray tracing, topographic features responsible for threedimensional effects of horizontal refraction and focusing are identified. These effects are observed in the measurements from the Shallow Water 2006 experiment. Specifically, signals from a pair of fixed sources recorded on a horizontal line array sitting on the seafloor show an intensification caused by horizontal focusing due to the seabed topography of 4 dB along the array.