Long range monitoring of explosive volcanoes with IMS infrasound arrays: testing the VIS

Detecting and promptly reporting ongoing volcanic eruptions is crucial in supporting Volcanic Ash Advisory Centers (VAACs) in their mission to inform about ash clouds that may endanger aviation. Nevertheless, many active volcanoes lack local monitoring systems. Long-range infrasound monitoring, which holds the potential to detect and notify volcanic explosive events, could offer valuable insights. Numerous studies have already emphasized the utility of long-range infrasound data for this purpose, which led to the proposal of several monitoring approaches. 
The Volcanic Information System (VIS), developed in the framework of the FP7 and H2020 ARISE projects, is one of the most recent approaches for reporting ongoing eruptive events in near real-time based on process data from a single infrasound array. However, uncertainties still persist regarding its effectiveness and reliability. VIS is based on the Infrasound Parameter, IP, a detection algorithm originally developed for local monitoring and later adapted to long-range volcanic infrasound observations.
In this study, we investigate the efficiency of VIS considering 10 years (2010-2019) of data provided by 16 infrasound arrays of the International Monitoring System (IMS) established and provisionally operated by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO). These 16 arrays are located in the most active volcanic regions of the world, encompassing multiple eruptions that range in energy from mild explosions to eruption classified with a VEI (Volcanic Explosivity Index) ≥ 4. To evaluate the reliability of the VIS algorithm and estimate the rate of false alerts (false positives), we compared the notifications provided for the entire period of analysis with reports from the Global Volcanism Program (GVP). 
Our results show that VIS is well designed for long-lasting (> few minutes), large (VEI >3) eruptions, such as Sub-Plinian/Plinian events or highly sustained Vulcanian/Strombolian explosions, while it typically misses single transient events. In terms of ranges, its reliability is strongly azimuth-dependent, with the best results at IMS range (up to 2000 km) achieved under favourable propagation conditions while limited to shorter distances (~1000 km) otherwise. Despite that improvements are possible by azimuthal deflation with the computational of 3D ray-tracing, unresolved ambiguity often remains due to the short angular distances between volcanoes with respect to the array. This issue can be solved by considering volcanic sectors rather than single edifices. In this context, we show that the VIS reliability significantly increases and might provide critical information to the VAACs, automatically and in near real-time, to trigger an independent analysis of ongoing volcanic eruptions.
This study was financially supported by the National Recovery and Resilience Plan, Mission 4 Component 2 - Investment 1.4 - NATIONAL CENTER FOR HPC, BIG DATA AND QUANTUM COMPUTING - funded by the European Union - NextGenerationEU - CUPB83C22002830001.