K. Cheng and Y. N. Huang, Ionospheric disturbances observed during the period of Mount Pinatubo eruptions in, J. Geophys. Res, vol.97, pp.16995-17004, 1991.

K. Igarashi, S. Kainuma, I. Nishimuta, S. Okamoto, H. Kuroiwa et al., Ionospheric and atmospheric disturbances around Japan caused by the eruption of Mount Pinatubo on 15, J. Atmos. Terr. Phys, vol.56, pp.1227-1234, 1991.

J. Zlotnicki, J. L. Le-mouël, R. Kanwar, P. Yvetot, G. Vargemezis et al., Ground-based electromagnetic studies combined with remote sensing based on Demeter mission: A way to monitor active faults and volcanoes, Planet. Space Sci, vol.54, pp.541-557, 2006.
URL : https://hal.archives-ouvertes.fr/hal-00272983

J. Zlotnicki, F. Li, and M. Parrot, Signals recorded by DEMETER satellite over active volcanoes during the period, Geophys. J. Int, vol.183, pp.1332-1347, 2004.
URL : https://hal.archives-ouvertes.fr/hal-00576140

J. Zlotnicki, F. Li, and M. Parrot, Ionospheric Disturbances Recorded by DEMETER Satellite over Active Volcanoes: From, Int. J. Geophys, vol.530865, 2004.
URL : https://hal.archives-ouvertes.fr/hal-01067157

A. Rozhnoi, M. Hayakawa, M. Solovieva, Y. Hobara, and V. Fedun, Ionospheric effects of the Mt. Kirishima volcanic eruption as seen from subionospheric VLF observations, J. Atmos. Sol.-Terr. Phys, vol.107, pp.54-59, 2014.

A. Piscini, D. Marchetti, and A. De-santis, Multi-parametric climatological analysis associated with global significant volcanic eruptions during 2002-2017, Pure Appl. Geophys, 2019.

W. Gringel, J. M. Rosen, and D. J. Hofmann, Electrical Structure from 0 to 30 km Atmospheric Electricity in the Planetary Boundary Layer: The Earth's Electrical Environment, pp.166-182, 1986.

S. A. Pulinets, K. A. Boyarchuk, V. V. Khegai, V. P. Kim, and A. M. Lomonosov, Quasi electrostatic model of atmosphere-thermosphere-ionosphere coupling, Adv. Space Res, vol.26, pp.1209-1218, 2000.

Z. Ulanowski, J. Bailey, P. W. Lucas, J. H. Hough, and E. Hirst, Alignment of atmospheric mineral dust due to electric field, Atmos. Chem. Phys, vol.7, pp.6161-6173, 2007.
URL : https://hal.archives-ouvertes.fr/hal-00296401

S. Pulinets and D. Davidenko, Ionospheric precursors of earthquakes and global electric circuit, Adv. Space Res, vol.53, pp.709-723, 2014.

O. Melnik and M. Parrot, Electrostatic discharge in Martian dust storms, J. Geophys. Res, vol.103, pp.29107-29118, 1998.

C. D. Stow, Dust and sand storm electrification, vol.24, pp.134-140, 1969.

G. D. Freier, The electric field of a large dust devil, J. Geophys. Res, vol.65, 1960.

W. D. Crozier, Dust devil properties, J. Geophys. Res, vol.75, pp.4583-4585, 1970.

A. K. Kamra, Measurements of the electrical properties of dust storms, J. Geophys. Res, vol.77, pp.5856-5869, 1972.

A. K. Kamra, Effect of Dust-Raising Winds on the Atmospheric Electric Field, Electrical Processes in Atmosphere, pp.168-174, 1977.

D. S. Schmidt, R. A. Schmidt, and J. D. Dent, Electrostatic force on saltating sand, J. Geophys. Res. Atmos, vol.103, pp.8997-9001, 1998.

T. L. Jackson and W. M. Farrell, Electrostatic fields in dust devils: An analog to Mars, IEEE Trans. Geosci. Remote Sens, vol.44, pp.2942-2949, 2006.

N. O. Renno and J. F. Kok, Electrical activity and dust lifting on Earth, Mars, and beyond, Planetary Atmospheric Electricity, pp.419-434, 2008.

H. F. Zhang, T. Wang, J. J. Qu, and M. H. Yan, An experimental and observational study on the electric effect of sandstorms, Chin. J. Geophys, vol.47, pp.53-60, 2004.

C. P. Saunders, Thunderstorm electrification, Handbook of Atmospheric Electrodynamics

H. Volland and . Ed, , pp.61-92, 1995.

M. C. Brook, B. Moore, and T. Sigurgeirsson, Lightning in volcanic clouds, J. Geophys. Res, vol.79, pp.472-475, 1974.

S. R. Brantley, The eruption of Redoubt volcano, U.S. Geol. Surv. Circ, p.33, 1989.

J. F. Paskievitch, T. L. Murray, P. Hoblitt, and C. A. Neal, Lightning associated with the August 18, 1992, eruption of Crater Peak vent, Mount Spurr volcano, Alaska. In The 1992 Eruptions of Crater Peak Vent, Mount Spurt Volcano, Alaska, vol.2139, pp.179-182, 1995.

S. R. Mcnutt and C. M. Davis, Lightning associated with the 1992 eruptions of Crater Peak Mount Spurr volcano, Alaska. J. Volcanol. Geotherm. Res, vol.102, pp.45-65, 2000.

R. J. Thomas, P. R. Krehbiel, W. Rison, H. E. Edens, G. D. Aulich et al., Electrical activity during the 2006 Mount St. Augustine volcanic eruptions, Science, vol.315, 1097.

K. Aizawa, A. Yokoo, W. Kanda, Y. Ogawa, and M. Iguchi, Magnetotelluric pulses generated by volcanic lightning at Sakurajima volcano, Japan. Geophys. Res. Lett, p.17301, 2010.

S. A. Behnke, R. J. Thomas, S. R. Mcnutt, D. J. Schneider, P. R. Krehbiel et al., Observations of volcanic lightning during the 2009 eruption of Redoubt Volcano, J. Volcanol. Geotherm. Res, vol.259, pp.214-234, 2013.

S. A. Behnke, R. J. Thomas, H. E. Edens, P. R. Krehbiel, and W. Rison, The 2010 eruption of Eyjafjallajökull: Lightning and plume charge structure, J. Geophys. Res. Atmos, vol.119, pp.833-859, 2014.

C. Antel, A. B. Collier, J. Lichtenbergerand, and C. J. Rodger, Investigating Dunedin whistlers using volcanic lightning, Geophys. Res. Lett, vol.41, pp.4420-4426, 2014.

M. R. James, S. J. Lane, and J. S. Gilbert, Volcanic plume electrification: Experimental investigation of a fracture-charging mechanism, J. Geophys. Res, vol.105, pp.16641-16649, 2000.

M. R. James, L. Wilson, S. J. Lane, J. S. Gilbert, T. A. Mather et al., Electrical charging of volcanic plumes, Space Sci. Rev, vol.137, pp.399-418, 2008.

T. A. Mather and R. G. Harrison, Electrification of volcanic plumes, Surv. Geophys, vol.27, pp.387-432, 2006.

P. Arason, A. J. Bennett, and L. E. Burgin, Charge mechanism of volcanic lightning revealed during the 2010 eruption of Eyjafjallajökull, J. Geophys. Res, vol.116, 2011.

S. R. Mcnutt and E. R. Williams, Volcanic lightning: Global observations and constraints on source mechanisms, vol.72, pp.1153-1167, 2010.

J. J. Berthelier, M. Godefroy, F. Leblanc, E. Seran, D. Peschard et al., IAP, the thermal plasma analyzer on DEMETER, Planet. Space Sci, vol.54, pp.487-501, 2006.
URL : https://hal.archives-ouvertes.fr/hal-00155500

J. P. Lebreton, S. Stverak, P. Travnicek, M. Maksimovic, D. Klinge et al., The ISL Langmuir Probe experiment and its data processing onboard DEMETER: Scientific objectives, description and first results, Planet. Space Sci, vol.54, pp.472-486, 2005.

J. J. Berthelier, M. Godefroy, F. Leblanc, M. Malingre, M. Menvielle et al., ICE The electric field experiment on DEMETER, Planet. Space Sci, vol.54, pp.456-471, 2006.

J. Higgins and A. Harris, VAST: A program to locate and analyse volcanic thermal anomalies automatically from remotely sensed data, Comput. Geosci, vol.23, pp.627-645, 1997.

N. Pergola, F. Marchese, and V. Tramutoli, Automated detection of thermal features of active volcanoes by means of infrared AVHRR records, Remote Sens. Environ, vol.93, pp.311-327, 2004.

F. Marchese, C. Filizzola, N. Genzano, G. Mazzeo, N. Pergola et al., Assessment and improvement of a robust satellite technique (RST) for thermal monitoring of volcanoes, Remote Sens. Environ, vol.115, pp.1556-1563, 2011.

A. Piscini and V. Lombardo, Volcanic hot spot detection from optical multispectral remote sensing data using artificial neural networks, Geophys. J. Int, vol.196, pp.1525-1535, 2014.

F. Marchese, M. Neri, A. Falconieri, T. Lacava, G. Mazzeo et al., The Contribution of Multi-Sensor Infrared Satellite Observations to Monitor Mt. Etna (Italy) Activity during May to, Remote Sens, vol.10, 1948.

A. J. Prata, Observations of volcanic ash clouds in the 10-12mm window using AVHRR/2 data, Int. J. Remote Sens, vol.10, pp.751-761, 1989.

A. J. Prata, Infrared radiative transfer calculations for volcanic ash clouds, Geophys. Res. Lett, vol.16, pp.1293-1296, 1989.

P. N. Francis, M. C. Cooke, and R. W. Saunders, Retrieval of physical properties of volcanic ash using Meteosat: A case study from the 2010 Eyjafjallajökull eruption, J. Geophys. Res, vol.117, 2012.

A. J. Prata and A. T. Prata, Eyjafjallajökull volcanic ash concentrations determined using Spin Enhanced Visible and Infrared Imager measurements, J. Geophys. Res. Atmos, vol.117, pp.1-23, 2012.

Y. Guéhenneux, M. Gouhier, and P. Labazuy, Improved space borne detection of volcanic ash for real-time monitoring using 3-Band method, J. Volcanol. Geotherm. Res, vol.293, pp.25-45, 2015.

J. Li, P. Zhang, T. J. Schmit, J. Schmetz, and W. P. Menzel, Technical note: Quantitative monitoring of a Saharan dust event with SEVIRI on Meteosat-8, Int. J. Remote Sens, vol.28, pp.2181-2186, 2007.

L. Klüser and K. Schepanski, Remote sensing of mineral dust over land with MSG infrared channels: A new Bitemporal Mineral Dust Index, Remote Sens. Environ, vol.113, pp.1853-1867, 2009.

F. Sannazzaro, C. Filizzola, F. Marchese, R. Corrado, R. Paciello et al., Identification of dust outbreaks on infrared MSG-SEVIRI data by using a Robust Satellite Technique (RST)

, Acta Astronaut, vol.93, pp.64-70, 2014.

V. Tramutoli, Robust AVHRR Techniques (RAT) for Environmental Monitoring: Theory and applications, Earth Surface Remote Sensing II

E. Zilioli and . Ed, , vol.3496, pp.101-113, 1998.

V. Tramutoli, Robust Satellite Techniques (RST) for Natural and Environmental Hazards Monitoring and Mitigation: Theory and Applications, Proceedings of the 2007 International Workshop on the Analysis of Multi-temporal Remote Sensing Images, 2007.

E. Sardón, A. Rius, and N. Zarrao, Estimation of the transmitter and receiver differential biases and the ionospheric total electron content from global positioning system observation, Radio Sci, vol.29, pp.577-589, 1994.

J. Y. Liu, H. F. Tsai, and T. K. Jung, Total electron content obtained by using the global positioning system, Terr. Atmos. Ocean. Sci, vol.7, pp.107-117, 1996.

H. F. Tsai and J. Y. Liu, Ionospheric total electron content response to solar eclipses, J. Geophys. Res, vol.104, pp.12657-12668, 1999.

F. N?mec, O. Santolík, and M. Parrot, Decrease of Intensity of ELF/VLF Waves observed in the Upper Ionosphere close to Earthquakes: A Statistical Study, J. Geophys. Res. Space Phys, vol.114, pp.1-10, 2009.

Y. He, D. Yang, J. Qian, and M. Parrot, Response of the ionospheric electron density to different types of seismic events, Nat. Hazards Earth Syst. Sci, vol.11, pp.2173-2180, 2011.
URL : https://hal.archives-ouvertes.fr/insu-01180088

D. Pí?a, F. N?mec, O. Santolík, M. Parrot, and M. Rycroft, Additional attenuation of natural VLF electromagnetic waves observed by the DEMETER spacecraft resulting from pre-seismic activity, J. Geophys. Res. Space Phys, vol.118, pp.5286-5295, 2013.

A. Eleftheriou, C. Filizzola, N. Genzano, T. Lacava, M. Lisi et al., Long-Term RST Analysis of Anomalous TIR Sequences in Relation with Earthquakes Occurred in Greece in the Period, Pure Appl. Geophys, vol.173, pp.285-303, 2004.

T. Lacava, C. Filizzola, N. Pergola, F. Sannazzaro, and V. Tramutoli, Improving flood monitoring by the Robust AVHRR Technique (RAT) approach: The case of the April 2000 Hungary flood, Int. J. Remote Sens, vol.31, pp.2043-2062, 2010.

C. S. Grimaldi, D. Casciello, I. Coviello, T. Lacava, N. Pergola et al., An improved RST approach for timely alert and Near Real Time monitoring of oil spill disasters by using AVHRR data, Nat. Hazards Earth Syst. Sci, vol.11, pp.1281-1291, 2011.

C. Filizzola, R. Corrado, F. Marchese, G. Mazzeo, R. Paciello et al., Erratum to RST-FIRES, an exportable algorithm for early-fire detection and monitoring: Description, implementation, and field validation in the case of the MSG-SEVIRI sensor. Remote Sens, vol.186, pp.196-216, 2017.

F. Marchese, G. Mazzeo, I. Coviello, A. Falconieri, C. Filizzola et al., Issues and possible improvements in winter fires detection by satellite radiances analysis: Lesson learnt in two regions of Northern Italy, J. Sel. Top. Appl. Earth Obs. Remote Sens, vol.10, pp.3297-3313, 2017.

F. Marchese, A. Falconieri, N. Pergola, and V. Tramutoli, A retrospective analysis of the Shinmoedake (Japan) eruption of 26-27, J. Volcanol. Geotherm. Res, vol.269, pp.1-13, 2011.

N. Pergola, V. Tramutoli, F. Marchese, I. Scaffidi, and T. Lacava, Improving volcanic ash cloud detection by a robust satellite technique, Remote Sens. Environ, vol.90, pp.1-22, 2004.

F. Marchese, F. Sannazzaro, A. Falconieri, C. Filizzola, N. Pergola et al., An enhanced satellite-based algorithm for detecting and tracking dust outbreaks by means of SEVIRI data, vol.9, 2017.

D. Ouzounov, S. Pulinets, A. Romanov, A. Romanov, K. Tsybulya et al., Atmosphere-Ionosphere Response to the M9 Tohoku Earthquake Reviled by Joined Satellite and Ground Observations, Earthq. Sci, vol.24, pp.557-564, 2011.

D. Ouzounov, S. Pulinets, K. Hattori, and P. Taylor, Pre-Earthquake Processes: A Multi-disciplinary Approach to Earthquake Prediction Studies

. Agu/wiley, , vol.385, 2018.

D. Ouzounov, D. Liu, C. Kang, G. Cervone, M. Kafatos et al., Outgoing Long Wave Radiation Variability from IR Satellite Data Prior to Major Earthquakes, Tectonophysics, vol.431, pp.211-220, 2007.

V. Tramutoli, G. Di-bello, N. Pergola, and S. Piscitelli, Robust satellite techniques for remote sensing of seismically active areas, Ann. Geophys, vol.44, pp.295-312, 2001.

V. Tramutoli, V. Cuomo, C. Filizzola, N. Pergola, and C. Pietrapertosa, Assessing the potential of thermal infrared satellite surveys for monitoring seismically active areas: The case of Kocaeli (Izmit) earthquake, Remote Sens. Environ, vol.96, pp.409-426, 1999.

M. Hernández-pajares, J. Juan, J. Sanz, R. Orus, A. Garcia-rigo et al., The IGS VTEC maps: A reliable source of ionospheric information since 1998, J. Geod, vol.83, pp.263-275, 2009.

S. Pulinets, D. Ouzounov, A. V. Karelin, and D. Davidenko, Physical bases of the generation of short-term earthquake precursors: A complex model of ionization-induced geophysical processes in the lithosphere-atmosphere-ionosphere-magnetosphere system, Geomagn. Aeron, vol.55, pp.521-538, 2015.

S. Calvari, M. Neri, and H. Pinkerton, Effusion rate estimations during the 1999 summit eruption on Mt. Etna, and growth of two distinct lava flow fields, J. Volcanol. Geotherm. Res, vol.119, pp.107-123, 2002.

B. Behncke, M. Neri, and . The, , vol.65, pp.461-476, 2001.

S. Branca and P. Del-carlo, Types of eruptions of Etna volcano AD 1670-2003: Implications for short-term eruptive behavior, vol.67, pp.732-742, 2005.

F. Salvi, R. Scandone, and C. Palma, Statistical analysis of the historical activity of Mount Etna, aimed at the evaluation of volcanic hazard, J. Volcanol. Geotherm. Res, vol.154, pp.159-168, 2006.

C. Del-negro, A. Cappello, M. Neri, G. Bilotta, A. Hérault et al., Lava flow hazards at Mount Etna: Constraints imposed by eruptive history and numerical simulations, Sci. Rep, issue.3, 2013.

M. Neri, B. Behncke, M. Burton, G. Galli, S. Giammanco et al., Continuous soil radon monitoring during the, Geophys. Res. Lett, vol.33, p.24316, 2006.

D. Andronico, S. Scollo, A. Cristaldi, and F. Ferrari, Monitoring ash emission episodes at Mt. Etna: The 16 November 2006 case study, J. Volcanol. Geotherm. Res, vol.180, pp.123-134, 2009.

R. Wunderman and . Ed, Smithsonian Institution, Bulletin of the Global Volcanism Network, vol.31, p.17, 2006.

. Global-volcanism-program, In Bulletin of the Global Volcanism Network 31:8, Smithsonian Institution, p.12, 2006.

D. Andronico, C. Spinetti, A. Cristaldi, and M. F. Buongiorno, Observations of Mt. Etna volcanic ash plumes in 2006: An integrated approach from ground-based and polar satellite NOAA-AVHRR monitoring system, J. Volcanol. Geotherm. Res, vol.180, pp.135-147, 2009.

V. Amiridis, M. Kafatos, C. Perez, S. Kazadzis, E. Gerasopoulos et al., The Potential of the Synergistic Use of Passive and Active Remote Sensing Measurements for the Validation of a Regional Dust Model, Ann. Geophys, vol.27, pp.3155-3164, 2009.

N. Bègue, P. Tulet, J. P. Chaboureau, G. Roberts, L. Gomes et al., Long-range transport of Saharan dust over northwestern Europe during EUCAARI 2008 campaign: Evolution of dust optical properties by scavenging, J. Geophys. Res, vol.117, 2012.

M. Wiegner, S. Groß, V. Freudenthaler, F. Schnell, J. Gasteiger et al., Saharan dust event over Munich: Intensive aerosol parameters from lidar measurements, J. Geophys. Res. Atmos, vol.116, 2008.

H. Klein, S. Nickovic, W. Haunold, U. Bundke, B. Nillius et al., Saharan dust and ice nuclei over Central Europe, Atmos. Chem. Phys, vol.10, pp.14993-15022, 2010.

A. Piscini, S. Corradini, F. Marchese, L. Merucci, N. Pergola et al., Volcanic ash cloud detection from space: A comparison between the RSTASH technique and the water vapour corrected BTD procedure, Geomat. Nat. Hazards Risk, vol.2, pp.263-277, 2011.

A. Falconieri, M. C. Cooke, C. Filizzola, F. Marchese, N. Pergola et al., Comparing Two Independent Satellite-Based Algorithms for Detecting and Tracking Ash Clouds by Using SEVIRI Sensor, Sensors, vol.18, 2018.

R. Wunderman and . Ed, Smithsonian Institution, Bulletin of the Global Volcanism Network, vol.33, p.17, 2008.

. Global-volcanism-program, In Weekly Volcanic Activity Report, 2008.

, The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO), National Aeronautics and Space Administration, 2019.

V. A. Liperovsky, C. V. Meister, E. V. Liperovskaya, V. F. Davidov, and V. V. Bogdanov, On the possible influence of radon and aerosol injection on the atmosphere and ionosphere before earthquakes, Nat. Hazards Earth Syst. Sci, vol.5, pp.783-789, 2005.
URL : https://hal.archives-ouvertes.fr/hal-00299298

K. Heki, Explosion energy of the 2004 eruption of the Asama Volcano, central Japan, inferred from ionospheric disturbances, Geophys. Res. Lett, vol.33, p.14303, 2006.

M. J. Rycroft and R. G. Harrison, Electromagnetic atmosphere-plasma coupling: The global atmospheric electric circuit, Space Sci. Rev, vol.168, pp.363-384, 2012.

S. Pulinets and D. Ouzounov, Lithosphere-Atmosphere-Ionosphere Coupling (LAIC) model-An unified concept for earthquake precursors validation, J. Asian Earth Sci, vol.41, pp.371-382, 2011.

M. Parrot, J. Achache, J. J. Berthelier, E. Blanc, A. Deschamps et al., High-frequency seismo-electromagnetic effects, Phys. Earth Planet. Inter, vol.77, pp.65-83, 1993.

M. Parrot, J. J. Berthelier, J. P. Lebreton, J. A. Sauvaud, O. Santolik et al., Examples of unusual ionospheric observations made by the DEMETER satellite over seismic regions, Phys. Chem. Earth, vol.31, pp.486-495, 2006.

M. Hayakawa, Electromagnetic Precursors of Earthquakes: Review of Recent Activities, Rev. Radio Sci, pp.807-818, 1993.

O. A. Molchanov, A. Rozhnoi, M. Solovieva, O. Akentieva, J. J. Berthelier et al., Global diagnostics of the ionospheric perturbations related to the seismic activity using the VLF radio signals collected on the DEMETER satellite, Nat. Hazards Earth Syst. Sci, vol.6, pp.745-753, 2006.
URL : https://hal.archives-ouvertes.fr/hal-00330917

S. Sarkar, A. K. Gwal, and M. Parrot, Ionospheric variations observed by the DEMETER satellite in the mid-latitude region during strong earthquakes, J. Atmos. Sol.-Terr. Phy, vol.69, pp.1524-1540, 2007.

F. Muto, M. Yoshida, T. Horie, M. Hayakawa, M. Parrot et al., Detection of ionospheric perturbations associated with Japanese earthquakes on the basis of reception of LF transmitter signals on the satellite DEMETER, Nat. Hazards Earth Syst. Sci, vol.8, pp.135-141, 2008.
URL : https://hal.archives-ouvertes.fr/hal-00330928

E. Slominska, J. Blecki, M. Parrot, and J. Slominski, Satellite study of VLF ground-based transmitter signals during seismic activity in Honshu Island, Phys. Chem. Earth, vol.34, pp.464-473, 2009.

A. De-santis, G. De-franceschi, L. Spogli, L. Perrone, L. Alfonsi et al., Geospace perturbations induced by the earth the state of the art and future trends, Phys. Chem. Earth, vol.85, pp.17-33, 2015.
URL : https://hal.archives-ouvertes.fr/insu-01270603

A. De-santis, G. Balasis, F. J. Pavón-carrasco, G. Cianchini, and M. Mandea, Potential earthquake precursory pattern from space: The 2015 Nepal event seen by magnetic Swarm satellites, vol.461, pp.119-126, 2017.

J. Y. Liu, Y. I. Chen, Y. J. Chuo, and C. S. Chen, A statistical investigation of pre-earthquake ionospheric anomaly, J. Geophys. Res, vol.111, 2006.

M. Li and M. Parrot, Statistical analysis of an ionospheric parameter as a base for earthquake prediction, J. Geophys. Res. Space Phys, vol.118, pp.3731-3739, 2013.
URL : https://hal.archives-ouvertes.fr/insu-01178983

P. Han, K. Hattori, M. Hirokawa, J. Zhuang, C. Chen et al., Statistical analysis of ULF seismomagnetic phenomena at Kakioka, J. Geophys. Res. Space Phys, vol.119, pp.4998-5011, 2001.

A. European-space, , p.12, 2019.

C. Satellite, , p.12, 2019.

, This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license, © 2019 by the authors. Licensee MDPI