title: An airborne acoustic method to reconstruct a dynamically rough flow surface.
abstract: Currently, there is no airborne in situ method to reconstruct with high fidelity the instantaneous elevation of a dynamically rough surface of a turbulent flow. This work proposes a holographic method that reconstructs the elevation of a one-dimensional rough water surface from airborne acoustic pressure data. This method can be implemented practically using an array of microphones deployed over a dynamically rough surface or using a single microphone which is traversed above the surface at a speed that is much higher than the phase velocity of the roughness pattern. In this work, the theory is validated using synthetic data calculated with the Kirchhoff approximation and a finite difference time domain method over a number of measured surface roughness patterns. The proposed method is able to reconstruct the surface elevation with a sub-millimeter accuracy and over a representatively large area of the surface. Since it has been previously shown that the surface roughness pattern reflects accurately the underlying hydraulic processes in open channel flow [e.g., Horoshenkov, Nichols, Tait, and Maximov, J. Geophys. Res. 118(3), 1864-1876 (2013)], the proposed method paves the way for the development of non-invasive instrumentation for flow mapping and characterization that are based on the acoustic holography principle.
authors.affiliation: Department of Mechanical Engineering, University of Sheffield, Sheffield, S1 3JD, United Kingdom.
authors.forename: Anton
authors.initials: A
authors.lastname: Krynkin
authors.affiliation: Department of Mechanical Engineering, University of Sheffield, Sheffield, S1 3JD, United Kingdom.
authors.forename: Kirill V
authors.initials: KV
authors.lastname: Horoshenkov
authors.affiliation: Department of Information Technology, Ghent University, Sint-Pietersnieuwstraat 41, 9000 Gent, Belgium.
authors.forename: Timothy
authors.initials: T
authors.lastname: Van Renterghem