Green’s functions for propagation of sound in a simply moving fluid

Two approaches involving the spatial and temporal Fourier transforms have been used to derive time‐ and space‐dependent Green’s functions pertinent to the propagation of sound waves in a fluid that is moving with a constant velocity v. The two approaches give rise to differing interpretations of the observations made by a stationary observer vis‐a‐vis those made by an observer moving with the fluid. The properties of the causal and the noncausal Green’s functions are analyzed, and are shown to be equivalent.