Atmospheric refraction effects on racetrack sound levels

This paper summarizes the results of a sound level study for a racetrack in Tampa, Florida to investigate potential ordinance compliance. The study consisted of three separate dates of measurements and captured significant examples of atmospheric refraction. The measurements collected during this study have shown that wind direction several hundred feet above the surface played a significant role on sound wave propagation in this area. In one instance, the race track light structures were visible from an upwind observer position but the races were inaudible whereas at an equidistant downwind position, the racetrack was loud with A-weighted sound levels 20–30 dB greater than background sound levels. This paper presents the measured sound levels and meteorological conditions at positions within a two mile radius of the track, for each of the three test dates, and provides an example of the potential variability of sound levels that can be encountered during ordinance compliance monitoring. A simple long range propagation model for this area is included along with the application of a method to account for the effect of upwind and downwind conditions on received sound levels.