PROPAGATION IN AN INVERSION AND REFLECTIONS AT THE GROUND

The propagation of sound is considered for an atmosphere in which the sound velocity increases linearly with height. For source and receiver separation large compared with their heights above the ground, there are in general four possible ray paths between source and receiver having a given number of ground reflections n≳1. For n=0, i.e., no reflections, there is one ray path; and for n=1 there are three possible ray paths. By suitable grouping of the ray paths it is possible to evaluate the effects of reflection at a ground of known, finite impedance (especially near the source), assuming coherence between neighboring rays; and also to evaluate the net sound intensity of waves traveling via more widely separated paths in the normally turbulent atmosphere assuming incoherence. A temperature inversion is found, using ray theory, to increase the sound level at large horizontal distances inside the shadow region due to finite surface impedance, that is otherwise predicted by wave theory for a neutral atmosph...