Cylindrical Fourier near-field acoustical holography applied to a high-power jet

Near-field acoustical holography as a method to reconstruct sound fields near military jet aircraft is being investigated. Measurements were recently made on the F-22 Raptor using a linear, ground-based array of microphones at a distance of 11 m from the centerline. Analytic continuation is used to extend the measurement aperture, and, assuming axisymmetry, cylindrical Fourier near-field acoustical holography is used to reconstruct the sound field. Because of the highly directional nature of the source and the effects of wrap-around error from the Fourier transform, the desired reconstruction distance (10–20 m) and the number of points to analytically continue the measurement are directly proportional. Furthermore, given the measurement standoff distance, inverse propagation to the source requires near-complete regularization of the evanescent wave components. [Work supported by Air Force SBIR.]