Estimation of angle-dependent absorption coefficients from spatially distributed in situ measurements

A method is proposed for measuring the angle-dependent absorption coefficient of a boundary material in situ. The method relies on decomposing a non-uniform three-dimensional pressure distribution, measured in the vicinity of a boundary, into plane-wave components (i.e., via estimation of its wavenumber transform). The incident and reflected plane-wave components at the boundary are separated in the wavenumber domain, from which it is possible to deduce an absorption coefficient for each angle of incidence simultaneously. The technique is used to verify theoretical predictions of the angle-dependent absorption coefficient of an absorbing ceiling, based on in situ measurements in a conventional room.