Survey of the relationship of level fluctuations of outdoor public emergency broadcasting sound with meteorological conditions using observations of unattended noise monitoring

摘要

This paper describes a result of survey on level fluctuations of sound propagation over ground due to meteorological effects using regularly broadcasting sound from an outdoor public emergency address system. At Narita International Airport, there are a lot of unattended stations for continuous monitoring of aircraft noise located at various sites around the airport. There are also a lot of broadcasting loudspeakers installed at various places, such as on the top of school and/or community center buildings, for an outdoor public emergency address system, which usually broadcasts time signals and/or short-duration music regularly in order to be prepared for unforeseen real emergency broadcasting. Those sounds are observed as single sound events at the noise monitor and often disturb monitoring of aircraft noise. However, if we look at it from a different angle, we can utilize it as a means of investigating level fluctuations of sound propagation over ground due to meteorological effects, because it regularly generates a definite and fixed-level sound signal at a fixed time every day. Thus, we have extracted noise observations of the public emergency broadcasting sound from a mass of noise data observed at various noise monitoring stations and analyzed the relationship of level fluctuations of outdoor public emergency broadcasting sound with meteorological conditions. As a result, it turned out that level fluctuation becomes larger as the propagation distance becomes longer and that it has a relation to vector wind, predominant wind direction and season as the parameter.