ASA 127th Meeting M.I.T. 1994 June 6-10

3aAO5. Small scale flow inversion by diffraction tomography.

Daniel Rouseff

Kraig B. Winters

Appl. Phys. Lab., Univ. of Washington, Seattle, WA 98105

The reconstruction of a moving fluid from acoustic transmission experiments is considered. To fully characterize the fluid, inversion for both the scalar index of refraction and the vector velocity fields describing the flow is desired. A standard approach is to use rays as a forward model for the acoustics. At sufficiently short ranges, refraction can be neglected and a straight-ray transmission assumed. By measuring the time-of-flight through the flow from many directions, the index of refraction can be recovered. The full vector velocity field, however, cannot be recovered; the inversion is underdetermined within the assumed forward model. In this talk, a linearized time-harmonic wave equation is used to model the acoustics. It is shown that within this model a unique inversion for the vector flow velocity is possible. The result is a distinctly finite wavelength result indicating why ray-based methods fail to produce a full reconstruction. [Work supported by ONR.]