Beam sweeping in sediment layer using phase-conjugated pseudo sound sources

Abstract

When an object that is buried in a sediment layer is detected from the diagonal, detection is hampered by reflection from the bottom surface. Stated in different terms, the sound-wave energy that reaches the object is small because of the reflection and refraction that occurs at the bottom surface when a sound wave is applied to the object in the sediment for diagonal detection. To alleviate that problem, a pseudo sound source can be set up in sediment layer. The sound wave radiated from the pseudo sound source is then received by a time-reversal array. The sound wave can be injected into the sediment layer by reversing the received signal with time and radiating it again from the time-reversal array. The beam can hit the target through movement of this pseudo sound source along the bottom surface. The sound wave that hits the target is reflected and returns in water. The sound wave is subsequently reflected many times at the surface and bottom and is diffused over time. The passive-phase conjugate processing is then given to the received diffusing signal to reduce this diffusion. The pulse is compressed by this processing, thereby obtaining the target position. a)Currently at NDA; b)Currently at JAMSTEC; c)Currently at Univ. of Tsukuba.