26 luglio 2016

Etna ash monitoring - The Department X-band mobile radar using dual polarization

To monitor the spatial distribution of volcanic clouds at middle and long distance from the point of emission, are normally used geostationary satellites operating in the infrared and visible channels. The images that return every 15-30 minutes, however, offer a reduced spatial resolution and the comments are greatly hampered by the presence of clouds weather. For these reasons the optimal solution for real-time monitoring of these phenomena is represented by the radar stations that provide higher spatial resolution and acquisition frequency, as well as the ability to make observations at night and under any conditions of cloud cover.

Although radars were born for detecting hydrometeors - rain, snow, hail - the Civil Protection Department wanted to exploit the maximum potential offered by this type of instrumentation, enriching the national radar network, created in recent years with great commitment of resources, with a particular type of mobile radar in the X-band dual polarization. Compared with conventional weather radars, the X-band guarantees a greater sensitivity in the identification of fine particles, while the dual-polarization ensures higher data quality.

An X-band radar was then installed in January 2010, at the airport of Catania Fontanarossa to monitor volcanic ash clouds emitted from Etna and support the authorities responsible for regulation and control of air traffic. An identical instrument was sent to Iceland instead of following the eruption of the volcano Eyjafjallajokull in April 2010 to provide support to 'Icelandic Met Office and the local aviation authorities, and to be tested and calibrated to operate in difficult environmental conditions and ashes of relapse.

After a phase of development which lasted for several months, on April 10 last year, the radar Catania Fontanarossa for the first time detected and tracked in a clear manner the plume of volcanic ash that has been developed by the South Crater Etna spreading east towards the south-eastern areas to a few tens of kilometers and up to an estimated at least 8500 meters above sea level. After several hours of activity, at 16 the eruptive phenomenon has ceased and the plume is slowly diluted into the atmosphere.

The radar observations, unique features for both instrumental and for proximity to the crater, represent an important result and the foundations are laid for the future full integration of the instrument in the monitoring system. The tool offers the possibility of an objective in the atmosphere for the calibration of predictive models of dispersal, and could usefully be included in future aviation procedures for flight safety in case of eruptive activity.