Advanced GPS products for Volcanos Monitoring applied at Mount Etna

The GPS electromagnetic waves that propagate in the neutral atmosphere are perturbed by the local characteristics of the crossed medium. Variations of pressure, temperature and water content, together with the presence of hydrometeors and particulates, cause changes in the refractive index along the ray path. Since 1988, the INGV-OE monitors ground deformation at Mt. Etna. Nowadays, the network geometry consists of 42 permanent stations that provide a dense coverage of the volcano edifice. Owing to both the high frequency of explosive episodes and the well-developed GPS network, Mt. Etna is particularly suited for an in-depth investigation into the potential of GPS technique in the volcanos monitoring. Within the EC FP7 APhoRISM and MED-SUV projects, two main issues have been addressed: the wet tropospheric tomography to improve the precision of the Differential Interferometry Synthetic Aperture Radar (DInSAR) technique and the capability of GPS in detecting the volcanic plumes. The DInSAR technique, used in geodesy to monitor the volcanic areas, is affected by atmospheric artefacts that are quite the most significant and, probably, the most difficult to identify and reduce. Due to the prominent topography of Etna volcano and the quite variable weather conditions, the atmospheric heterogeneities become even more pronounced. The estimation of atmospheric anomalies using GPS measurements have noticeable importance to establish the “effective” ground deformation of the volcanic edifice. A software has been developed for deriving the tropospheric tomography starting from the GAMIT software output. The wet refractivity tomography was applied on experimental data of DInSAR Sentinel1 IW on Mount Etna. Concerning the second topic, in the last years the Mt. Etna high frequency explosive activity formed volcanic plumes that rose up to kilometers above the vent. We investigate the ability of GPS to detect volcanic plumes at Etna through the analysis of the GPS Signal to Noise Ratio (SNR) data. The SNR data provide no information about the distance between the satellite transmitting the signal and receiver, and thus make no direct contribution to positioning solutions. However, the SNR data are important because they can directly measure signal attenuation or blockages. We develop and test the method on the volcanic plume produced during some explosive episodes. Results show that, during the eruption, the SNR data had a drop caused by the presence of dense ash-laden plumes.