Sediment tomography in the East China Sea: Compressional wave speed and attenuation inversions from mode travel time dispersion and Airy phase measurementsa)

Abstract

This paper discusses ongoing data analysis results from the acoustic bottom interaction experiment conducted in May–June 2001 in the East China Sea as part of the Asian Seas International Acoustics Experiment (ASIAEX‐2001). Using time‐frequency scalograms of broadband signals, the modal arrivals and group speed minimums (Airy Phase) of several modes are clearly observed. The structure of the Airy Phase signal forms the basis of this inversion technique. Utilizing the Airy Phase group speed minimums and corresponding pressure amplitudes of each observable mode, the sediment compressional wave speed and attenuation as a function of depth are derived. The group speed minimum for each mode provides additional information on the compressional wave speed in the modal sediment depth penetration interval. Inverted speeds and estimated modal penetration depths are then used to develop the sediment profile. The estimated resolution is dependent on the number and frequency span of the observable modes. This method has the advantage of utilizing only one hydrophone to obtain rapid estimates of sediment properties. Additionally, it also complements other inversion schemes that can benefit from accurate a priori environmental information by limiting the size of the search parameter space. Estimated sediment properties from several areas are presented with verification from coring results. [Work supported by ONR.] a)For Acoustical Oceanography Best Student Paper Award.