Atmospheric Ray Tracing based on altitude-dependent weather data
Master Thesis of Schäfer, Philipp
This thesis addresses sound propagation in the atmosphere in the context of auralization of acoustic scenes. A common method to estimate sound paths between a given source and receiver is the so called ray tracing. With the help of these estimated paths, an impulse response can be derived, which allows the auralization of acoustic scenes in a virtual environment. In contrast to the acoustic medium in rooms, where ray tracing is commonly used, the atmosphere is neither homogeneous nor static. Main reasons for this are the variation of the sonic speed over space and movement of the medium, such as wind. These effects lead to refraction and translation of sound resulting in curved ray paths. Additionally, distances between source and receiver are rather large in outdoor scenarios. Therefore, ray density around the receiver is low and prediction of ray paths needs high computational effort. This impedes finding eigenrays - rays, that directly hit the receiver - since it is complex but needs to be efficient for fast computations of the impulse response. In the course of this thesis, a ray tracing algorithm for the simulation of atmospheric sound propagation and auralization is designed. Ray propagation is investigated to determine criteria for finding and neglecting rays, that are irrelevant for the receiver, in an early state to save computation time. Altitude-dependent weather data is used to model atmospheric properties assuming the atmosphere to be a stratified medium. In a second step, the influence of these properties on the impulse response is investigated. Therefore, an acoustic scene is rendered repeatedly while varying the weather parameters.