Multipulse acoustic tomography: A new technique for mapping water temperatures

Abstract

Ocean acoustic tomography is a traveltime tomography technique that can be used to map the sound-speed field in a given region of water. Ocean acoustic tomography and other travel-time tomography techniques use the time-of-flight for a signal sent between a sender and receiver to infer information about the conditions of the region under study. Traditionally, such techniques assume that for each sender-receiver pair, one data point can be obtained from the time-of-flight: the average speed-of-sound along the path. In this paper we introduce multipulse acoustic tomography, a new travel-time tomography technique that uses a sequence of bi-directional pulses as the acoustic signal. By analyzing the difference in traveltime between pairs of pulses traveling in the same and opposite direction we can distribute the change in average speed-of-sound into sub-regions along the acoustic path. The result is a much more detailed picture of the distribution in speed-of-sound between a sender-receiver pair. Such a detailed distribution can be used to improve reconstruction techniques or to obtain high resolution results with fewer nodes. We present the system design and design constraints for multipluse acoustic tomography along with simulation results that show the technique can separate local speed-of-sound changes along an acoustic path from the average.