We developed a high frequency split beam (SB) scientific echo sounder to measure the target strength of a zooplankton in situ. There are some issues for high frequency split beam method, namely, an accuracy of transducer, a high speed processing of phase detection and a calibration method. We discussed about the following provisions : Piezocomposite transducer, high speed phase detection device for mobile phone and tungsten carbide sphere.
We have researched on the application of time reversal waves to the underwater acoustic technology. Time reversal waves enable a desired signal to converge to the focus, even in unknown and inhomogeneous media. As time reversal waves converge to a “point” at any range, their focusing property is quite different from that of the conventional beam forming method. In this study, the basic research on time reversal communication is carried out. By using time reversal, the reflected and refracted waves are converged to the focus, the signal level received at the focus is increased and the symbol interferences are reduced. However, in order to ensure the communication channel only with time reversal, it is necessary to install many transducers of time reversal array. So, in this study, it is proposed to combine the focusing effect of time reversal waves and conventional adaptive filter. After most of the multi-path waves are utilized by using time reversal, unfocused waves, which appear like “noise”, are removed by adaptive filter. The simulations in shallow water are performed and it is concluded that this proposed method makes more accurate communication to the long distance possible than the conventional method.