Wave propagation in a duct with boundary scattering (with application to a surface duct)

Scattering integrals are derived that represent the contribution of boundary scattering in a sound channel. These integrals are added to the normal mode sum which represents the coherent field in the channel. A comparison is made between experimental and calculated sound levels in a surface duct. For the case examined, it is clear that (except for short ranges) surface scattered energy is a significant source of sound at a below duct receiver.