The barometric-pressure sensor as a comparison-calibration reference for acoustics from 0.01 to 10 hertz

A reference acoustic sensor with well-characterized complex frequency response from DC to several hertz would enable comparison-calibration of transducers and arrays designed for detection, localization, and characterization of infrasonic acoustic events. That frequency range is challenging for established calibration techniques. One conventional approach is to use an infrasound measurement microphone as a comparison-calibration reference; however, as frequency decreases below a few hertz, the uncertainty in the microphone response typically increases. In a comparison calibration, that uncertainty contributes directly to the uncertainty in response of the sensor under test. An alternate approach, described in this paper, uses a "barometric" sensor-a sensor with known response at zero frequency-as a comparison-calibration reference. The goal is to bridge the region from DC to tens of hertz with a low-pass model for the complex frequency response of the barometric reference while preserving the low uncertainty of that reference. In this way, a laboratory lacking primary-calibration capability could perform traceable comparison calibrations with low uncertainty in the hundredths to tens of hertz region.