On the use of a polarimetric X-band weather radar for volcanic ash clouds monitoring

The retrieval of volcanic ash cloud properties is of significant interest due to their environmental, climatic and socio-economic effects. Ash fallout can cause substantial hardship and damages in volcano's surrounding area and represents a serious hazard to aircrafts as well. Volcanic ash is usually composed by silicates and, once they are sucked up by jet engines of modern airplanes, they can fuse in the combustion chamber. In order to monitor ash cloud pattern and concentration, satellite visible-infrared radiometric observations from geostationary satellites (e.g., Meteosat sensor) are usually exploited for long-range trajectory tracking and for measuring low level eruptions. Their imagery is available every 15-30 minutes and suffers from a relatively poor spatial resolution (i.e., order of some kilometers). Moreover, the field-of-view of geostationary radiometric measurements may be blocked by water and ice clouds at higher levels and their overall utility is reduced at night. Satellite data fro radiometric sensors aboard near-polar orbiting platforms can also be employed to detect and map volcanic ash clouds over the entire globe. The usefulness of these sensors is limited by their relatively poor temporal resolution, guaranteeing only two over-passes per day at most using a single platform. Among the remote sensors, ground-based microwave weather radars may represent an important tool to detect and, to a certain extent, mitigate hazards from the ash clouds in proximity of the volcano vent. The possibility of monitoring in all weather conditions at a fairly high spatial resolution (less than few hundreds of meters) and every few minutes after the eruption is the major advantage of using ground-based microwave radar systems. The use of weather radars to observe ash eruptions is still quite limited, and most radar observations of volcanic eruptions are occasionally carried out by meteorological radars of national weather services. In spite of this potential and the fact that weather radar use dates back to early eighties, there are still open issues about microwave weather radar capabilities to quantitatively retrieve volcanic ash cloud parameters. In this work the polarimetric ash signature at X-band is retrieved using data recently collected by an operational radar system located in Sicily (Italy) near the Etna volcano. Starting from the results of previous studies, this work is aimed at: i) verifying the effectiveness of polarimetric electromagnetic models of ash particles; ii) setting-up a mass concentration retrieval algorithm.