Sediment tomography in the East China Sea: Preliminary results

Abstract

This paper discusses the early results from the acoustic bottom interaction experiment conducted in May–June 2001 in the East China Sea as part of the ASIAEX-2001. Explosive sources (38 g and 1000 g) were deployed in the experimental area from a Chinese Research vessel (Shi Yan 2) during the experiment. These shots are deployed in circular pattern of radius 30 km and on radial tracks. The acoustic signals from these explosive sources were received at the vertical line array hung from R/V Melville near the center of the circular pattern. The sediment properties show a sharp contrast on either side of a sediment front. The presence of high-speed sand and low speed mud–sand on either side of the front has been confirmed by core data from ASIAEX-2000. Extensive coring to determine the sediment information in more detail is planned in August 2001. The time-frequency scalograms of the received explosive signals have been constructed using wavelet analysis. This analysis yields the dispersion characteristics of the acoustic signals and clearly shows the modal arrivals. The dispersion behavior of the acoustic modes from either side of this sediment front is presented. These modal dispersion diagrams form the basis for our sediment inversion technique. [Work supported by ONR.]