Source height determination by ground effect inversion in the presence of a sound velocity gradient

A propagation inversion method has been devised and tested that enables determination of height of a sound source which is above an acoustically soft ground. The horizontal separation between the point source and receivers is assumed to be a priori knowledge. The proposed algorithm is site adaptive since it makes use of the predicted influence of the ground on near-grazing propagation over flat, continuous ground surfaces and of the predicted influence of a stable refracting atmosphere. Stable refraction has been included in the analysis by assuming a linear sound velocity gradient in the otherwise quiescent atmosphere. This represents a first step towards an atmospheric equivalent of the matched field processing technique used in underwater acoustics. Extensive measurements have been carried out over two test sites with different ground impedance characteristics. The spectra of the acoustic signals used in the analysis were between 50 Hz and 2000 Hz and the grazing angle of each measurement varied from 5° to 8°. The algorithm has been shown to allow accurate deduction of the source height from a priori knowledge of the range where the range varies from 50 m to 100 m in one site and from 130 m to 175 m in the other site.