Scattering by moving bodies: The quasi stationary approximation

The scattered field produced by a rotating or vibrating object in the presence of a time harmonic plane wave is usually approximated by a time dependent sequence of stationary fields, called a quasi stationary field. Recently the mathematical theory of scattering of scalar fields of Lax and Phillips has been extended to cover moving bodies. Within this framework the quasi stationary approximation is shown to be valid in each sphere of finite radius which contains the body. Far fields for the exact field and the quasi stationary field are defined and the difference is estimated in terms of a small parameter.