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Thirty infrasound sensors have been operated over Japan since 2015. We developed the irregular array data processing in order to detect and estimate the parameters of the arrival source waves by using infrasound data related to the sequence of the volcanic eruption at Mt. Shinmoedake in March 2018. We found that the apparent velocity at the ground was equal to the acoustic velocity at particular reflection levels. The results were confirmed through a comparison of the findings of the apparent velocity with a wave propagation simulation on the basis of the azimuth, infrasound time arrivals, and the state of the atmospheric background using global atmospheric models. In addition, simple ideas for estimating horizontal wind speeds at certain atmospheric altitudes based on infrasound observation data and their validation and comparison were presented. The calculated upper wind speed and wind observed by radiosonde measurements were found to have a qualitative agreement. Propagation modeling for these events estimated celerities in the propagation direction to the sensors that were consistent with the tropospheric and stratospheric ducting. This study could inspire writers, in particular, and readers, in general, to take advantage of the benefits of infrasound wave remote-sensing for the study of the Earth’s atmospheric dynamics.

We investigated meteor height and number of meteor echoes over a 13‐year observation period, with the data recorded by the meteor wind radar systems in Kototabang (0.20°S, 100.32°E) and Biak (1.17°S, 136.10°E), Indonesia. We aimed to investigate the changes in meteor peak height according to solar activity, represented by the solar radio index F10.7, and the number of solar sunspots, R, compared with the empirical results of the Mass Spectrometer Incoherent Scatter Extending (MSISE) and Committee on Space Research International Reference Atmosphere models. We found that (i) the daily meteor count rates at both sites in the period from 2003 to 2016 could be used to determine the dynamics in the upper atmosphere, where peak conditions occurred in the middle of the year; (ii) through a statistical approach using the normal distribution function, the variation in meteor peak height showed a positive correlation with the trend in solar activity; and (iii) comparison between the two empirical models and our observations showed two points where annual air density seemed to have a clear relationship with peak meteor height. In addition, the annual neutral density pattern of the model was related to the daily meteor count every year, although it showed a pattern opposite to the solar activity trends.

We report on the measurements of radio frequency interference (RFI) at Mount Timau, Kupang, Indonesia, which is intended to host a future radio astronomy observatory. These measurements were taken twice in October 2020 and December 2020 to obtain the RFI environment, at frequencies between 70 and 7000 MHz. Due to the limitations of the measurement data, the results presented in this paper are based on peak detection rather than statistical analysis. Based on the measurement results, the frequency interval between 70–88 MHz and 120–150 MHz is relatively quiet, and the frequency range of 150–300 MHz is relatively clear. The frequency interval of 300 to 800 MHz is relatively quiet, except at the frequency of 600 MHz. The frequency range of 800–1400 MHz is also relatively quiet. The predominant terrestrial services in this band are at 840 MHz, with an amplitude around 32 dB, and 916 MHz, with an amplitude around 12 dB, and the global system for mobile (GSM) signals around 954 MHz have an amplitude around 20 dB above the noise floor. The frequency range of 1400–7000 MHz is also relatively quiet. In this band frequency, we can see RFI at 2145 and 2407 MHz, emitted by local Wi-Fi, and at 2683 MHz, with amplitudes of 18, 40 and 15 dB, respectively, from the noise level. We conclude that, for this period, the frequency band allocated for astronomy can possibly be used for radio telescope development.