Sound beam scanning in sediment layer using phase conjugated pseudo sound source

Abstract

When an object that is buried underwater in a sediment layer is detected from the diagonal, detection is often hampered by reflection from the bottom surface. Stated in different terms, the sound-wave energy that reaches the object is small because of 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 the 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.

Numerical Simulation of Target Range Estimation Using Ambient Noise Imaging with Acoustic Lens

“…In Japan, underwater acoustic communications applying TRM have been studied by Shimura et al [25][26][27][28][29][30] Kikuchi et al and Tsurugaya et al have also studied several underwater acoustics applications of TRM. [31][32][33][34] Figure 1 shows our approach. In the forward propagation, the scattering waves from the target are generated by the natural ambient noise sources and are converged by the lens.…”

“…24) In the last 20 years, many studies of TRM have been conducted for applications to underwater acoustics. In Japan, underwater acoustic communications applying TRM have been studied by Shimura et al [25][26][27][28][29][30] [31][32][33][34] Figure 1 shows our approach. In the forward propagation, the scattering waves from the target are generated by the natural ambient noise sources and are converged by the lens.…”

Focal Depth Shifting of Phase-Conjugate Wave in Pekeris Waveguide

“…Research studies of the movement of the focus are divided roughly into three studies of the method of using a pseudosound source, the method of the movement in the direction of range, and the method of the movement in the direction of depth. The study of the method of using the pseudosound source 16) is the research to determine which focus is moved by moving the pseudosound source using the characteristic that the sound wave converges in the source location. In the method of the movement in the direction of range, the focus is moved by shifting frequency using a wideband signal.…”