Traffic Noise and the Hyperbolic Plane

Abstract

We consider the problem of sound propagation in a wind. We note that the rays, as in the absence of a wind, are given by Fermat's principle and show how to map them to the trajectories of a charged particle moving in a magnetic field on a curved space. For the specific case of sound propagating in a stratified atmosphere with a small wind speed we show that the corresponding particle moves in a constant magnetic field on the hyperbolic plane. In this way we give a simple `straightedge and compass' method to estimate the intensity of sound upwind and downwind. We construct Mach envelopes for moving sources. Finally, we relate the problem to that of finding null geodesics in a squashed anti-de Sitter spacetime and discuss the $SO(3,1)\times \mathbb{R}$ symmetry of the problem from this point of view.

Typos corrected

References in corpus (2)

• Stationary Metrics and Optical Zermelo-Randers-Finsler Geometry
• Godel metric as a squashed anti-de Sitter geometry

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• A Spacetime Geometry picture of Forest Fire Spreading and of Quantum Navigation
• On the application of Lorentz-Finsler geometry to model wave propagation