Laboratory and at-sea experiments using a vertical synthetic array technique to measure the sound waves propagating above and below fluid-saturated sediment interfaces

Abstract

A series of measurements in the NRL shallow water laboratory were designed and conducted to measure the sound waves propagating in an un-consolidated fluid-saturated porous medium. The novel design used a pair of small receivers, one buried in the bottom and one mounted in the water column to a linear vertical positioner. The buried receiver was carefully inserted into the sandy bottom using a small water-jet, engineered to have no entrained air, to minimally disturb the bottom. The receiver pair were incrementally pulled up through the bottom or water column to map out the sound propagating from a source mounted in the water column. The position of the source was varied to measure above critical angle and below critical angle sound penetration into the bottom. Measurements of carefully smoothed and roughened interfaces were also conducted. This synthetic vertical array technique proved very successful in the laboratory and was transitioned to at-sea measurements in a variety of sandy bottom locations around Panama City, FL. The analysis and modeling of these laboratory and at-sea experiments will be discussed.A series of measurements in the NRL shallow water laboratory were designed and conducted to measure the sound waves propagating in an un-consolidated fluid-saturated porous medium. The novel design used a pair of small receivers, one buried in the bottom and one mounted in the water column to a linear vertical positioner. The buried receiver was carefully inserted into the sandy bottom using a small water-jet, engineered to have no entrained air, to minimally disturb the bottom. The receiver pair were incrementally pulled up through the bottom or water column to map out the sound propagating from a source mounted in the water column. The position of the source was varied to measure above critical angle and below critical angle sound penetration into the bottom. Measurements of carefully smoothed and roughened interfaces were also conducted. This synthetic vertical array technique proved very successful in the laboratory and was transitioned to at-sea measurements in a variety of sandy bottom locations aro...