| A Simple Acoustic Scattering Model for Ensembles of Rocks and Seashells Lying on the Ocean Floor |
24 JUL 1998 |
26 pages |
| Authors:
Christopher Feuillade; Mel D. Wagstaff; Roger W. Meredith; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS HIGH FREQUENCY ACOUSTICS SECTION
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 | This report describes a computer model for predicting levels of acoustic scattering at sonar frequencies from an important class of clutter objects, i.e., rocks and seashells lying on the ocean floor. A simplified modeling approach has been adopted that incorporates basic concepts and principles. Rocks are represented by either grid movable spheres or elastic spheres, a technique that has been previously used to model aqueous ... |
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| Environmental Measurements and Observations in Support of the Naval Research Laboratory's High Frequency Acoustic Coherence Experiments, Panama City 1995 |
SEP 96 |
42 pages |
| Authors:
Christine T. Mire; Roger W. Meredith; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS HIGH FREQUENCY ACOUSTICS SECTION
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| From 30 March to 19 April 1995, the Naval Research Laboratory conducted a series of high frequency acoustic coherence measurements in the shallow-water (6-12 m) coastal environment off Panama City Beach, FL. This report contains descriptions of the equipment used to collect the data, the data quantity and quality, plots and tabulations, and an analysis of the oceanographic environment in which the acoustic data were collected. From 30 March to ... |
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| Modeled High-Frequency Acoustic Backscattered Levels from Range- Independent and Simplistic Range-Dependent Sand Bottoms |
21 FEB 96 |
17 pages |
| Authors:
Kristen D. Savage; Roger W. Meredith; NAVAL RESEARCH LAB STENNIS SPACE CENTER MS
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| Results investigating the effects of variable bottom composition on modeled high-frequency backscattered levels are presented for a typical shallow- water, variable bottom (range-dependent) environment. The modeled environment consisted of a single sound speed profile, a flat sea bottom with range- dependent bottom composition, and a smooth, flat sea surface. Coarse-and fine- grained sandy areas were partitioned in range to create range dependence. Bottom backscattering and reflection loss for each partition ... |
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| Under-Ice Broadband Transient Measurements and Processing |
JAN 92 |
26 pages |
| Authors:
Roger W. Meredith; NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
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| This report examines the horizontal spatial coherence of broadband acoustic energy in the frequency range 100-1200 Hz from explosive sources under the ice pack. The data were recorded on four hydrophone pairs with a nominal sensor separation of 370 m from source ranges from 3 to 25 km. Mean-square coherence is computed separately for the direct and ice-reflected propagation paths, and octaveband frequency averaging reduces variability inherent in the coherence ... |
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| Impact of Sample Window Choice and Location on Time Delay Estimation of Transients |
01 DEC 89 |
2 pages |
| Authors:
Roger W. Meredith; Allen E. Lyebourne III; NAVAL OCEANOGRAPHIC AND ATMOSPHERIC RESEARCH LAB STENNIS SPACE CENTER MS
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| Estimation of time delays between coherent transient signals is biased by the choice and location of the sampling window. For transients that do not tend to zero within the sampling window (self-windowing), the uniform or boxcar window may not be the best choice due to spectral leakage. This is especially important when processing highly asymmetrical transient signals that are not self windowing as in the case of acoustic ambient noise. ... |
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| Environmental Variability at Site Alfa during the Broadband-87 Exercise |
AUG 89 |
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| Authors:
Paul J. Bucca; Roger W. Meredith; NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY STENNIS SPACE CENTER MS
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 | The Broadband-87 acoustics exercise was an at-sea efforts designed to characterize broadband propagation. This experiment was conducted in two areas of the North Atlantic Ocean Site Alfa, 31 N, 76 W, was chosen for its acoustically bottom-limited conditions and characteristically stable oceanographic environment. Site Delta, 28 N, 67 W, represented an area in which the sound channel is unobstructed by the seafloor. This report documents the comprehensive set of environment ... |
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| Environmental Measurements and Analysis: Arctic Acoustics Experiments in the Marginal Ice Zone |
AUG 89 |
75 pages |
| Authors:
Roger W. Meredith; Paul J. Bucca; Kim McCoy; NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY ARLINGTON VA
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| From 27 April through 28 May 1988, personnel from NORDA and other institutions used the USCGC Northwind to establish an ice camp to conduct an environmental acoustics exercise in the Marginal Ice Zone (MIZ) between Greenland and Svalbard in the Fram Strait. This report documents the comprehensive set of environmental data collected in support of the acoustic measurements. These data include expendable bathythermographs, conductivity- temperature-depth profiles, both vertical and time ... |
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| Oceanographic Measurements with Microprocessors |
JAN 88 |
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| Authors:
Paul J. Bucca; Roger W. Meredith; NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY NSTL STATION MS
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| Oceanographic data acquisition is usually done with instrumentation that has taken many hours to configure, program, and learn to use. The advent of self-recording oceanographic data collection systems based on microprocessors has greatly facilitated the acquisition of oceanographic data from ships of opportunity and in harsh environments. Two notable examples are the Ocean Data Equipment (ODEC) model 302A CSTD unit, which measures ocean conductivity, salinity, and temperature as a function ... |
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| Performance Comparison of the Wagstaff-Berrou and Maximum Entropy Method Beamformers |
APR 87 |
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| Authors:
Roger W. Meredith; Dan J. Ramsdale; NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY NSTL STATION MS
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| The performances of the maximum entropy method (MEM) and Wagstaff- Berrou broadhand (WB squared) high-resolution spatial processing techniques are compared with each other and with the conventional fast Fourier transform (FFT) beamformer. The comparisons are based on the analysis of three sets of measurements acquired at sea during two different environmental acoustics field exercises. Chosen for comparison are the effects of signal-to-noise ratio (SNR) on beamwidth and the effect of ... |
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| The Ocean Data CSTD Macintosh System |
SEP 86 |
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| Authors:
Roger W. Meredith; Paul J. Bucca; NAVAL OCEAN RESEARCH AND DEVELOPMENT ACTIVITY NSTL STATION MS
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| The Ocean Data Model 302A CSTD oceanographic profiling system is self-recording, preprogramming device. The system has been integrated with the Apple Macintosh computer to yield a portable, durable and easy-to-use system for measuring ocean conductivity, temperature, and salinity as a function of depth, and for calculating accurate sound speed values (roughly + or - 0.2 m/sec) for acoustic and oceanographic analysis and data quality assurance. This system enables the user ... |
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