THE EFFECT OF SURFACE REFLECTIONS ON DIRECTIVE SOUND SOURCES
Abstract
Reflections from the sea surface affect the acoustic power radiated by sound sources located at shallow depths. Furthermore, these surface reflections produced propagation anomalies characterized by a pattern of interference fringes and, at larger range, by abnormally high spreading losses known as the acoustic Lloyd mirror effect. Both phenomena are well-known for simple, non-directional sources. They are studied here for directive sources whose directivity patterns have a horizontal or tilted main lobe. Directive sources differ from simple sources in that the surface-reflected and direct rays are of different intensity. This causes a marked blurring of the interference fringe pattern, but has a negligible effect on the propagation anomaly at the long ranges where the Lloyd mirror effect holds. This is illustrated quantitatively for a horizontal end-fire directive array. The effect on power output of phase cancellations and reinforcements by surface-reflected sound waves is generally less marked than for a simple source. This is illustrated quantitatively for a vertical linear array of elements vibrating in phase. The Appendix presents the effect of rigid and pressure release reflectors on the directivity patterns and power outputs of variously oriented multipole sources. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 06, 1961
- Accession Number
- AD0259193
Entities
People
- M.c. Junger
- W. Jr. Thompson