ABSTRACT
This chapter explores the analytical basis for using ray tracing outdoors. There are distinct advantages in assuming a linear effective sound speed profile in ray tracing since this assumption leads to circular ray paths and analytically tractable solutions. R. Makarewicz and P. Kokowski have suggested a simple semi-empirical form for carrying out calculations of the variation in A-weighted levels from a stationary source for ranges up to 150 m allowing for wavefront spreading and ground effect. After further approximation for near-grazing incidence, inclusion of exponential factors to allow for A-weighting, source spectrum, air absorption and turbulence, and integration over frequency, an expression for the A-weighted mean square sound pressure may be deduced. Conditions of weak refraction may be said to exist where, under downward-refracting conditions, the ground-reflected ray undergoes only a single bounce, and, under upward-refracting conditions, the receiver is within the illuminated zone.
