Kariya Infrasound Database (1984-2004)

Abstract on this data set

A tripartite array of sensitive capacitor microphones was installed on the campus of the Aichi University of Education in Kariya, Japan (35.05N, 137.05E) in 1984 and operated until 2004 by Prof. Makoto Tahira. The frequency range of the microphones is 0.04-1Hz. Detection of weak infrasonic signals in these frequencies is often made difficult by noise caused by atmospheric turbulence. A device to reduce the wind noise has been developed by Tahira (1981) and adopted in the observations at Kariya. This is a multi-pipe line microphone attached to the infrasonic sensor. The principle of this noise reducer is to take an average of the pressure fluctuations along a line to cancel out uncorrelated wind noise, and is similar to the one proposed by Daniels (1959). The shape, however, is different from the original device given by Daniels. This line microphone consists of a number of parallel pipes of the same diameter, while Daniels' line microphone is a single pipe whose diameter changes stepwise at the inlet openings.

The output signals from the individual microphones are transmitted to one location by cables. After applying the numerical filter, the cross-correlation coefficients between all the pairs of the microphone outputs for 2-min time windows and averaged their maximum values over the three pairs. Traveling signals were identified when this averaged maximum reached a threshold, i.e., 0.6.

This database consists of three parts:

  1. 1984-1991: The traveling signals were picked up by looking at the chart record without calculating the correlation function. Therefore, the number of the events is smaller than the events elected automatically. The sampling frequency is 20Hz.
  2. 1993 – 2004: The traveling signals were detected automatically by calculating the cross-correlation coefficients as described above. The sampling frequency is 10Hz.
  3. 1991 Pinatubo eruption events: The data of this interval were treated differently from other period. The sampling frequency was around 8Hz and the data were recorded continuously.

Original values, band-pass filtered values and their plots are put as three types of separate files.

Rules of data use

This database is open for academic use but not for any operational or commercial purposes. Please acknowledge with appropriate style when you publish a manuscript by using this database. An example of acknowledgments would be as follow: “These infrasound data were supplied by M. Tahira at Aichi University of Education.”

Address for contact

Data Analysis Center for Geomagnetism and Space Magnetism,
Graduate School of Science, Kyoto University,
Kyoto 606-8502, Japan.
FAX: +81-75-722-7884
E-mail: iyemori@kugi.kyoto-u.ac.jp

Notes

  1. Two types of data files, i.e., original and band-pass filtered, and one plot file are available for each event.
    igaYYYYMMDDHH.ifs(1984-1990):original
    igaYYYYMMDDHHMM.ifs(1991-2004):original
    igaYYYYMMDDHH.bpf(1984-1990):band-pass filtered
    igaYYYYMMDDHHMM.bpf(1991-2004):band-pass filtered
    igaYYYYMMDDHH.gif(1984-1990):GIF image file of data plot
    igaYYYYMMDDHHMM.gif(1991-2004):GIF image file of data plot
    Artificial noises sometimes appear, but they are not removed.
  2. The absolute accuracy of the clock is about 1 second for most of the period. However, for 1993-1994, the time code could not be available and the clock of the PC were used. Therefore a few minutes error could exist.
  3. JST (Japan Standard Time) is used in this dataset.
    JST = UTC + 9hours
  4. The location of three sensors is as follow (see Figure 1).
    IGAYA-E (IGE):(35.050029432N, 137.053477763E)
    IGAYA-W (IGW):(35.052285212N, 137.048156262E)
    IGAYA-N (IGN):(35.055319658N, 137.05160737E)

Sample data plot

Acknowledgments

The construction of this database has been supported in part by grant 20244081 under the Japan Society for Promotion of Science (JSPS) and by the grant for the Inter-university Upper atmosphere Global Observation NETwork, IUGONET.