Influence of short-term meteorological variations over flat grass-covered ground on noise level fluctuation and application of mean meteorological data to noise prediction

Abstract

For environmental noise prediction, it is practicable to use meteorological data available from local meteorological observatories. However, these observations have limitations induced by the methods of measuring and data processing. Usually only mean meteorological values averaged over one 10 min period every hour are calculated. To apply these mean meteorological variables to noise propagation appropriately, we need to investigate the characteristics of both acoustic and meteorological parameters within the 10 min period. We made simultaneous measurements of both parameters over flat grass-covered ground and estimated effective sound speed profiles by similarity theory, using the meteorological data measured under conditions similar to those at local observatories. The changes in sound pressure level in periods around sunrise and sunset were similar and were smaller than those around culmination, in which fluctuations of approximately 20 dB were measured at higher frequencies at a distance of 100 m. Noise predictions by the parabolic equation method and sound speed profiles determined from instantaneous meteorological variations generally agreed with the measurements except in the time period around culmination. When we used 10 min mean meteorological values in combination with the parabolic equation method, we obtained reasonable agreement with the measurements at middle frequencies in time periods around sunrise and sunset.