[M-TT45] Brand-new scope of coupling geophysics being established by infrasound and associated waves

[MTT45-P07] select some parameters of the small-scale experimental device that can generate infrasound multiple times at arbitrary timing .

*Tomomi Tanaka¹, Masa-yuki Yamamoto¹ (1.Kochi University of Technology)

We developed a small-scale experimental device that can generate infrasound multiple times at arbitrary timing, and selected some parameters of the device that can observe infrasound aboard a sounding rocket flying at high altitude. The sound propagation characteristics of infrasound in the upper atmosphere have not been fully elucidated. We need to improve the number and quality of the observed signal and continue to verify the results. At present, direct measurements in the mesosphere and thermosphere at altitudes between about 50 km and 250 km are available only for a few tens of seconds to a few minutes during the passage of a rocket. The atmospheric pressure conditions at the altitude of 40 to 100 km, where experiments can be performed with the rocket, are simulated by a vacuum chamber in laboratory.In this study, we used a method to generate infrasound by instantaneously releasing compressed nitrogen gas. A solenoid valve is installed between the nitrogen gas cylinder and the jet output, and the solenoid valve is controlled by our developed software on a small PC, Raspberry Pi, to enable instantaneous jetting at any timing. By varying the positional relationship between the jets and the microphones that serve as infrasound sensors, the pressure exerted from the cylinders, the duration of the jets, and the degree of choke throttling, we selected equipment conditions that would allow us to observe the experiment inside the rocket flight. We also checked that all the equipment could be used without any problems in a low-pressure environment. When the pressure was adjusted to that of the upper atmosphere at an altitude of around 40 km (20-25 Pa) using a vacuum chamber, and Nitrogen gas was injected for 0.5 s with a distance of 15 cm between the jet output and the sensor, a choke scale of 1 of 8, and a gas cylinder pressure of 0.3 MPa, the results expected for observation at the actual launch were obtained. The peak output was 37 Pa, which is considered to be a sufficient value not to be missed in the noise as an output amplitude for the pressure condition around 40 km altitude where the noise during flight is large. If the output waveform does not sink significantly after the detection of the large amplitude signal, it is possible that the microphone capacitor recovers its function as a sensor earlier than the results of the recover time in this study. In the future, it is necessary to verify in detail the time required for the sensor to recover its function using a different sound source than the one developed after the sensor detects the large amplitude signal. We used a vacuum chamber to adjust the air pressure at altitudes of 40, 60, 80, and 100 km, and confirmed that all the devices could be used without any problems in the low-pressure environment under the device conditions selected in the previous experiment. The highest amplitude was obtained under the pressure condition at 40 km. The reason for this was that there were many atmospheric molecules moved by environmental gas, and sparse and dense waves were easily generated. In other words, as the altitude increases, the ambient noise might become smaller, so if the atmospheric pressure at 40 km altitude is high enough not to be missed in the noise, it can be observed at an altitude of 60 km or higher. As a conclusion, when the distance between the jet output and the sensor was 15 cm, the choke scale was 1, and gas was injected for 0.5 s at a primary pressure of 0.3 MPa, the actual measurement results were obtained, which can be expected to be observed even in a rocket in upper atmosphere.