Infrasounds are atmospheric sounds below the 20 Hz threshold of human hearing. Infrasounds can travel thousands of kilometres and can be detected using sensitive microbarometers. Several natural sources generate infrasounds, including the hundreds of volcanoes surrounding Singapore. In this project, we plan to build an infrasound array to detect and classify recorded signals of all origins (anthropic and natural). Real-time analysis of these signals can help identify the region where volcanic activity occurs. Coupled with other EOS projects, these regions can be associated with a probability of ash hazard over major cities in Southeast Asia.

Because volcanic infrasound is generated during the explosive release of fluid into the atmosphere, it is a robust indicator that an eruption has occurred. Therefore, long-range infrasonic monitoring may help to detect volcanic explosions and complement other monitoring technologies, especially in remote regions with sparse ground-based instrument networks.

In Singapore, this technology is particularly interesting to detect, locate and characterise major volcanic eruptions at long ranges. The main objective of this project is to recover physical information on volcanic eruptions detected by one station composed of 5 infrasonic sensors. This acoustic antenna will be used to detect coherent signals within the background noise and estimate the wavefront parameters of the waves (direction of arrival, speed, amplitude, dominant frequency, etc.). These parameters will provide useful information on the source and chronology of the eruption processes. This can lead to an independent and rapid diagnosis of the location and explosivity of an eruption, and thus to a first order notification of potential ash dispersal over Singapore Air-Space and major cities in Southeast Asia. Once the real-time analysis has been tested and proven to be robust, results will be sent to the VAAC centres in charge of the region (namely Darwin and Tokyo) and to the Meteorological Service of Singapore (MSS) as a 24/7 monitoring tool.

In recent years, the team has successfully installed an infrasound array in Singapore to record signals from distant volcanic eruptions, and to enable the eruption dynamics to be studied remotely.

What if we were able to remotely infer useful information about eruption chronology and released acoustic energy when a volcanic explosion occurs? In February 2014, the Kelut eruption in Indonesia (indicated by the yellow star) has demonstrated the potential of remotely recorded infrasound to quickly detect volcanic explosion and to characterise the source.