Calibration of sensors for airborne infrasound utilizing the hydrostatic pressure gradient

The reliable and comparable assessment of any physical quantity requires traceability to the international system of units (SI). Sound pressure is traditionally quantified using measurement microphones as transfer standards, for which the established primary calibration methods are currently limited to frequencies of 2 Hz and higher. These frequencies do not fully cover the range of interest for the International Monitoring System (IMS). For this reason, multiple calibration methods for airborne infrasound based on different physical principles are currently in development.

In this poster, a primary calibration method for the realization of the unit Pascal and a secondary calibration method for the transfer of the unit to field devices are presented. The primary calibration method utilizes the vertical gradient of the ambient pressure as stimulus. Moving a microphone periodically up and down subjects it to an alternating pressure with calculable amplitude. The secondary calibration, which transfers the unit to field devices such as microbarometers, is conducted as a comparison calibration in a closed chamber. Both the reference microphone and a device under test are placed in a closed chamber and subjected to a low-frequency alternating pressure. The sensitivity of the device under test is determined by comparison to the reference.

These methods extend the frequency range for the calibration of sensors for airborne infrasound to lower frequencies and improve the reliability of the assessment of airborne infrasound. In this contribution, the capabilities and limitations of both measurement setups are discussed.