A robust, low-cost and well-calibrated infrasound sensor for volcano monitoring

Abstract

Volcano acoustic signals contain valuable information on shallow magmatic and hydrothermal processes. In some cases, the detection of acoustic waves is the only clear evidence of the occurrence of volcanic explosions. Their study is thus complementary to that of seismic signals. For this reason, acoustic sensors are more and more frequently integrated in volcano monitoring systems as well as in temporary instrumental deployments. We have developed a broadband, robust and low-cost infrasound sensor designed for the detection and analysis of acoustic waves on volcanoes. It is based on a microelectromechanical differential pressure transducer (MEMS). The reference pressure is balanced with the atmospheric pressure through a pneumatic high-pass filter. Its low corner frequency, usually set to 60 mHz, can be adjusted from a few to tens of mHz. Its amplitude range is ±240 Pa and its sensitivity is 20 mV Pa−1, with a noise level <0.05 Pa RMS. The power consumption is 42 mW (3.5 mA with 12 V voltage). A direct output of the MEMS also provides a signal with sensitivity of about 500 μV Pa−1 and range ± 1245 Pa. This sensor is not sensitive to mechanical vibrations. The instrumental response of each infrasound sensor is carefully measured from 1 mHz to >100 Hz using two specially designed calibration systems which deliver sinusoidal pressure variations. The mechanical elements of the sensor are produced by 3D printer and filled with epoxy resin which guarantees high robustness in the aggressive environment of most volcanoes. The sensor dimensions (26x45x80 mm) and weight (100 g) makes it very easy to handle and install.