Formulas for ambient noise level and coherence

This paper investigates the various approximations commonly made in noise and noise coherence models and shows that in many cases a very simple ray approach can produce the same answers as full wave treatments such as RANDI-2. The solution presented here takes the form of a single angle integral which is valid for range-independent environments. Some closed-form solutions are presented, and the approach makes it very easy to understand such phenomena as the ''noise notch.'' The method can be extended to range dependence, and demonstrations are given of performance near a boundary (inhomogeneous field) and in the presence of nonuniform horizontal distributions of noise sources. (C) 1996 Acoustical Society of America.