Biomedical subjects

MD Collins

Publications and source records attributed to MD Collins.

3 recordsLinked to original sources

PubMed2000

Matched-field processing using measured replica fields

An approach for avoiding the problem of environmental uncertainty is tested using data from the TESPEX experiments. Acoustic data basing is an alternative to the difficult task of characterizing the environment by performing direct measurements and solving inverse problems. A source is towed throughout the region of interest to obtain a database of the acoustic field on an array of receivers. With this approach, there is no need to determine environmental parameters or solve the wave equation. Replica fields from an acoustic database are used to perform environmental source tracking [J. Acoust. Soc. Am. 94, 3335-3341 (1993)], which exploits environmental complexity and source motion.

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PubMed2000

A mapping approach for handling sloping interfaces

A mapping approach for handling sloping interfaces in parabolic equation solutions is developed and tested. At each range, the medium is rigidly translated vertically so that a sloping interface becomes horizontal. To simplify the approach, the slope is assumed to be small and the extra terms that arise in the wave equation under the mapping are neglected. The effects of these terms can be approximately accounted for by applying a leading-order correction to the phase. The mapping introduces variations in topography, which are relatively easy to handle for the case of a pressure-release boundary condition. The accuracy of the approach is demonstrated for problems involving fluid sediments. The approach should also be accurate for problems involving elastic sediments and should be useful for solving three-dimensional problems involving variable topography.

Journal Article↗

PubMed2000

An energy-conserving spectral solution

An energy-conserving spectral solution is derived and tested. A range-dependent medium is approximated by a sequence of range-independent regions. In each region, the acoustic field is represented in terms of the horizontal wave-number spectrum. A condition corresponding to energy conservation is derived for the vertical interfaces between regions. The accuracy of the approach is demonstrated for problems involving sloping ocean bottoms. The energy-conserving spectral solution is less efficient than the energy-conserving parabolic equation solution, but might be suitable for generalization to problems involving elastic bottoms.

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