Transfer function of the atmosphere over long distances

Philippe Delorme (1)

1 ONERA - The French Aerospace Lab [Châtillon]

Propagation in the atmosphere for long range seems to be a complex phenomenon: for instance the experimental observations of signals of Concorde sonic boom to several hundred kilometers where the classical N-waves disappears completely. In fact the transfer function of the atmosphere for the near field is a pure delay (propagation time) with a gain (corresponding to the geometric attenuation).At long range this physical model is not valid. It is well known for high frequency and long range it must be adjusted for the effects of viscosity. But this model must also be corrected at low frequencies because the atmosphere is not homogeneous and therefore diffracts. Based on the linearized Euler, it reveals a dimensionless number g.d /a2 (with g the gravitational constant, d the propagation distance and a the speed of sound). This number is of order 1 when the distance is about 10 km. The purpose of this paper is to show how the transfer function of the atmosphere changes when the propagation distance increases, assuming the latter is a stratified medium.

Domaines: Acoustique [physics.class-ph]

Philippe Delorme. Transfer function of the atmosphere over long distances. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00811135⟩