Numerical Modeling of a Time Reversal Experiment in Shallow Singapore Waters

The time reversal mirror (TRM) technique is a very useful tool in many underwater applications. Its usefulness in reverberation rejection and underwater communications has already been established through experiments by the Marine Physical Laboratory. The design of a TRM experiment is specific to the location and environment where it is being conducted. This paper presents theoretical and numerical analysis of a time reversal experiment which will be conducted in very shallow water (15 -20 m depth) in Singapore waters. The objective of the numerical simulation was to arrive at the various design parameters for the experiment and thus to predict its performance. The main parameters under question were the optimum frequencies to be used and the focusing ranges to be investigated. Extensive measurements were carried out at the selected site to obtain information about the ambient noise, time evolving sound speed structure and also the sound velocity in the sea-bed. The bottom sound speed was computed from the bulk density and porosity of the core samples collected from various locations at the site using an empirical formula Direct measurements were also done to find out the propagation losses at three different frequencies (7.5, 10 and 12.5 kHz) and at three different depths (4, 8 and 12 m) over a 500 m range. A short description of the system hardware also is presented.