Synthetic array measurements of acoustical waves propagating into a water-saturated sandy bottom for a smoothed and a roughened interface
Measurements of acoustical waves propagating in an unconsolidated water-saturated porous medium that involved the use of a two-dimensional synthetic array technique are presented. From these measurements, wave-front propagation is evaluated using time domain, wave-number frequency and two-dimensional spatial analysis techniques. First, a synthetic array measurement is employed to study sound penetration for a "smoothed" interface condition. This smoothed interface measurement is then compared to an identical synthetic array measurement with a "roughened" interface. A comparison of the smoothed and roughened interface measurements shows enhanced bottom penetration at shallow grazing angles as a result of the roughened interface. At shallow grazing angles, this scattered pressure from the roughened interface has the appearance of a wave front in the water-saturated porous medium that has a virtual wave speed of approximately 1200 m/s. Slower compressional waves in the sandy bottom are not observed.
Simpson
HJ
Physical Acoustics Branch, Naval Research Laboratory, Washington, DC 20375, USA. simpson@maddog.nrl.navy.mil
Houston
BH