Experimental study of ultra shallow water acoustic wave propagation

Abstract

The sound propagation in ultra shallow water was studied experimentally. The investigation was carried out in the nature pond approximately 300 × 20 m in size. Its depth was about 1 m. For such a pond critical frequency is about 700 Hz that is easy to emit and receive. The main purpose was to study the process of acoustic wave propagation in case of strong bottom influence and to restore some bottom parameters. The signal was radiated by the transducer and recorded by a set of point receivers located at different distances from the transducer. The signal was linear frequency modulated in 100 Hz–10 kHz band and was 10 s in duration. Its correlation with the recorded signal defines the pond response function. The modes representation was used. The group velocity frequency dependence was obtained by use of this method and it was very close to the theoretical one considering a soft bottom. The critical frequency also corresponded to the soft bottom model. The attenuation of sound was also studied in a wide frequency range including non-propagating mode. The results are very sensitive to the signal-to-noise ratio. It was shown that the used correlation method significantly improved the quality of obtained characteristics.