A Study of the Infrasonic Wave in the Atmosphere

[摘要] Continuous observation of the infrasonic wave has been recently started at Aichi Uni-versity of Education in Kariya City. Major interest is in the infrasounds frequently radiated into the atmosphere by the summit explosion of the volcano Sakura-jima.In detection of the infrasonic signal in the turbulent boundary layer, it is often indis-pensable to reduce the irregular noise caused by the turbulent fluctuation of the wind. In the present study, a new type of wind noise reducer has been designed. It is a multi-pipe line microphone, having a number of branches of pipes of equal diameter. The function of it is to take the equally-weighted spatial average of the pressure field along a straight line, and is essentially the same as the Daniels' line microphone (1959). However, the manufacturing of the multi-pipe line microphone is practically easier than the Daniels' type. Another merit of the new device is in that it is as easy to take the two-dimensional average if necessary.From several field tests, it has been shown that the wind noise is remarkably attenuated by the use of multi-pipe line microphone, although the measured noise attenuation has been smaller than the theoretical estimation based on the turbulence model given by Priestley(1965) by about 5dB in average.

[学科分类] 大气科学