Acoustic tomography on the basis of travel-time measurement

Abstract

Acoustic images of variable parameters of objects can be reconstructed by means of tomographic techniques which utilize the propagation of sound waves in the investigated medium. The technique described here utilizes sound frequencies in the audio range for acoustic imaging. The temperature-dependent sound speed as well as the flow field can be estimated by measuring the travel time of a defined acoustic signal between a sound source and a receiver when the distance between them is known exactly. The properties of the flow field are reconstructed using reciprocal sound rays to separate the direction-independent Laplace sound speed from the effective sound velocity. The temperatures in the flow field are then calculated by a combined inversion of all travel-time information resulting from the Laplace sound speed using an algebraic reconstruction technique. This reconstruction technique provides a cross section of the temperature distribution throughout the investigated area or volume. The tomographic system has been generalized to allow flow phenomena and temperature fields to be investigated with adapted sampling rates. The technique and procedures are exemplified by means of a scalable (from model-sized up to large-scale outdoor tomography) commercially oriented prototype of a tomograph which can utilize the whole audio and near-audio ultrasonic range. The software technology approach forms an inherent part of the realization.