Acoustical Tomographic Imaging of Flow Fields

P Holstein1, R Müller1, A Raabe2, M Barth2, D Mackenzie1, K Arnold2, A Ziemann2, M Schatz1 1 SINUS Messtechnik GmbH, Föpplstr. 13, D-04347 Leipzig, Germany, hol@sinusmess.de

2 Institute of Meteorology, University of Leipzig, Stephanstr. 3, D-04103 Leipzig, Germany

ABSTRACT

Acoustical 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 acoustical imaging. The sound speed as well as the flow field can be estimated by measuring the travel time of a defined acoustical signal between a sound source and a receiver when the distance between them is known exactly and a straight line sound propagation can be assumed. The distribution of the flow field is reconstructed using reciprocal sound rays to separate the direction-independent Laplace sound speed from the effective sound speed. 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 (SIRT - Simultaneous Iterative Reconstruction Technique). This reconstruction technique provides a cross-section of the temperature distribution of the investigated area. The tomographic technique 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.

Keywords tomography, audible frequencies, temperature fields, flow fields