Sensors and Actuators A 202 (2013) 13–22 Contents lists available at ScienceDirect Sensors and Actuators A: Physical jo ur nal homepage: www.elsevier.com/locate/sna A smart multisensor system for volcanic ash fall-out monitoring B. Andò ∗ , S. Baglio, V. Marletta, S. Medico Dipartimento di Ingegneria Elettrica, Elettronica e Informatica (DIEEI), University of Catania, V.le A. Doria 6, 95125 Catania, Italy a r t i c l e i n f o Article history: Available online 27 March 2013 Keywords: Volcanic ash Air transport safety Multisensor system Particle granulometry ROC analysis a b s t r a c t Ash fall-out following the explosive activity of volcanoes represents a factor of risk for people and a serious hazard for air traffic, especially if airports are close to the volcanic area. This is the case of the Fontanarossa airport located in Catania, in the south of Italy, close to the Etna volcano. Researchers at DIEEI are facing the challenge of developing a low-cost smart multisensor system to monitor the ash fall-out phenomenon by measuring the average granulometry of ash particles and the ash flow rate. Moreover, the system must be selective in respect to volcanic ash against others sediments such as dust, sand or soil. This paper is particularly focused on the methodology to be adopted for ash granulometry detection. The main idea is to use a piezoelectric transducer to convert ash impacts into electrical signals, which should provide information about the ash granulometry. Experimental results showing the suitability of the proposed approach are presented. Moreover, Receiver Operating Characteristic (ROC) analysis has been proposed as a theoretical support to properly implement the threshold mechanism aimed at ash granulometry classification. © 2013 Published by Elsevier B.V. 1. Introduction The atmospheric dispersion of ash released by the explosive activity of an active volcano is a relevant risk factor, such as hazard posed by the Etna volcano to the eastern area of Sicily in the south of Italy. Ash clouds cause extensive damage to roads, sanitation sys- tems [1], agriculture [2], health [3] and the daily activities of people living on the slopes of the volcano, and also forms a substantial haz- ard to air traffic (civil, commercial and military) [4]. Monitoring of ash fall-out is of great interest to meet logistical needs, as well as to achieve a better understanding of such phenomena and their ruling mechanisms. Due to the worldwide increase in volcanic explosion phenomena with consequent atmospheric ash dispersion, and in particular after the eruption of the Icelandic Eyafjallajokull volcano in 2010, the need of regulation for the safety of air transport has arisen. In response to this need, the International Civil Aviation Organization (ICAO) has issued guidance on managing flight operations into, or near, areas of known or forecast volcanic clouds [5]. During the eruptions of 2001 and 2002, the Fontanarossa air- port in Catania (at that time the third major airport in Italy in terms of numbers of passengers) was repeatedly declared DOI of original article: http://dx.doi.org/10.1016/j.sna.2013.01.056. ∗ Corresponding author. Tel.: +39 095 7382601; fax: +39 095 7387965. E-mail addresses: bruno.ando@dieei.unict.it (B. Andò), salvatore.baglio@dieei.unict.it (S. Baglio), vincenzo.marletta@dieei.unict.it (V. Marletta), stefaniamedico@gmail.com (S. Medico). inappropriate for take-offs and landings due to volcanic ash fall-out, creating great inconvenience to passengers along with financial loss for airlines and airport operators. During such crises, the decision to open or close the airport by the Italian Civil Aviation Author- ity resulted from subjective assessments, and therefore contained high levels of uncertainty and risk. As a consequence a scientific and technical commission has been established with the aim of regu- lating flight operations at airports in the presence of volcanic ash [6]. The National Institute of Geophysics and Volcanology (Istituto Nazionale di Geofisica e Vulcanologia, INGV) was designated a pri- mary source of information about eruptions that produce volcanic clouds. To cope with this service INGV is equipped with systems for monitoring ash clouds and forecasting their space-time evolution [7]. The latter provides decision support for aeronautical authorities in order to significantly reduce the factors of unpredictability, and therefore the impact of this phenomenon on airport infrastructure and flight operations. Traditional approaches for the monitoring of volcanic ash employ high-cost instrumentation, typically based on satellites [8] or X-Band dual-polarization radars [9]. Reliable instruments for ash granulometry classification, generally based on high-cost infrared cameras [10] and providing information on ash suspended in atmo- sphere, have been developed and deployed. These solutions allow discrete measurements at a restricted number of monitoring stations, thus guaranteeing a low spatial res- olution. Moreover, such systems are difficult to install and maintain and are often used to perform spot measurements. 0924-4247/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.sna.2013.03.027