GNGTS 2017 - 36° Convegno Nazionale

160 GNGTS 2017 S essione 1.2 Fig. 3 - Detrended and filtered data. GPS data. This is not surprising because, as already said, the N- S sensor is largely affected from noise and from poor resolution. Note that the vertical sensor data are in accordance with GPS based calculation: this individual sensor shows the best performance, really allowing a discrimination of a fraction of a microstrain over the whole period. This is a very promising result, constituting an example of what will be obtainable on each axes in second generation sensors. Considering that the data of the vertical axes are still affected by noise coming from the scarce deepness of the well (causing unwanted sensitivity to temperature excursions and to rain events), the potentiality to attain a long term resolution of few tens of nanostrain for each axes is quite clear. Conclusions. Our strain sensor prototype has been working for more than fifteen months (data acquisition is still going on) with limited period of default, showing to be a robust and reliable opto-electronic system. As already described elsewhere (Giacomelli et al. , 2017), two out of three axes have sensitivity enough to detect regional and teleseismic events, allowing a dynamic calibration. One of the sensors (N-S axes) suffers from poor sensitivity and large noise because of a problem of realisation. Anyway we learned the lesson about that, and we are confident that next generation instruments will be able to attain a resolution at the level of 10 nanostrain on all axes, together with a long term stability good enough to observe tridimensional soil strain. References DeWolf S.,Wyatt F.K., Zumberge M.A.,Hatfield W., 2015. Improved vertical optical fiber borehole strainmeter design for measuring Earth strain. Rev. of Scient. Instrum., 86, 114502 (2015); doi: 10.1063/1.4935923. Giacomelli U., Beverini N., Carbone D., Carelli G., Francesconi F., Gambino S., Maccioni E., Morganti M., Orazi M., Peluso R., Sorrentino F., 2017. Three-axial Fiber Bragg Grating Strain Sensor for Volcano Monitoring. Conf. FOTONICA 2017 AEIT, 19 th Edition, Padova May, 3-5 2017. MEDSUV Project, MEDiterranean SUpersite Volcanoes, 2013. http://www.med-suv.eu/ UNAVCO (A non-profit university-governed consortium, facilitates geoscience research and education using geodesy http://www.unavco.org/ ). Science Strainmeter Workshop, 2012. Working with strainmeter data. October 10-12 2012 Scripps Institution of Oceanography - UC San Diego. Organizing Committee Duncan Agnew, Scripps Institution of Oceanography, Evelyn A. Roeloffs, U.S. Geological Survey, Kathleen Hodgkinson, UNAVCO. UNAVCO Open-source tool, 2012 https://www.unavco.org/education/resources/modules-and-activities/majors-gps- strain/module-materials/gps-triangle-strain-calculator.xlsx