Distributed-Temperature-Sensing Using Optical Methods: A First Application in the Offshore Area of Campi Flegrei Caldera (Southern Italy) for Volcano Monitoring

Abstract

Abstract:A temperature profile 2400 m along the off-shore active caldera of Campi Flegrei (Gulf of Pozzuoli) was obtained by the installation of a permanent fiber-optic monitoring system within the framework of the Innovative Monitoring for Coastal and Marine Environment (MON.I.C.A) project. The system consists of a submerged, reinforced, multi-fiber cable containing six single-mode telecom grade optical fibers that, exploiting the stimulated Brillouin scattering, provide distributed temperature sensing (DTS) with 1 m of spatial resolution. The obtained data show that the offshore caldera, at least along the monitored profile, has many points of heat discharge associated with fluid emission. A loose association between the temperature profile and the main structural features of the offshore caldera was also evidenced by comparing DTS data with a high-resolution reflection seismic survey. This represents an important advancement in the monitoring of this high-risk volcanic area, since temperature variations are among the precursors of magma migration towards the surface and are also crucial data in the study of caldera dynamics. The adopted system can also be applied to many other calderas which are often partially or largely submerged and hence difficult to monitor.

Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors

“…Sensors based on optical fibers [45][46][47][48][49][50][51][52][53][54][55][56][57][58] are currently widely used for monitoring infrastructures, bridges, dams, buildings and landslides with many inherent advantages [45] including i) resistance to electromagnetic interference, ii) light weight, iii) small size, iv) high sensitivity, v) high-temperature performance, vi) immunity to corrosion and vii) large bandwidth [46].…”

“…Among the techniques based on SBS, the Brillouin Optical Time Domain Analyse (BOTDA) methodology [46,52,54,56], due to its powerful signal and spatial resolution, was considered suitable and, therefore, adopted for monitoring the buttress at the Lorano marble quarry. Data were obtained using the OSD-1 system [58] (Figure 6a) provided by the company Optosensing S.r.l. The OSD-1 system, which was periodically checked both on site and remotely via PC, is a control unit able to send the logs directly to a centralized enterprise-type database.…”

Monitoring of Strain and Temperature in an Open Pit Using Brillouin Distributed Optical Fiber Sensors

“…Sensors based on optical fibers [45][46][47][48][49][50][51][52][53][54][55][56][57][58] are currently widely used for monitoring infrastructures, bridges, dams, buildings and landslides with many inherent advantages [45] including i) resistance to electromagnetic interference, ii) light weight, iii) small size, iv) high sensitivity, v) high-temperature performance, vi) immunity to corrosion and vii) large bandwidth [46]. DOFS are cables of optical fiber which offer the possibility of monitoring variations of one-dimensional structural physical fields along the entire optical fiber in a truly distributed way [51,52].…”

Long-Term Monitoring with Fiber Optics Distributed Temperature Sensing at Campi Flegrei: The Campi Flegrei Deep Drilling Project

“…Since 1981 researchers have tried to introduce and apply new temperature monitoring methods using optical fibers [ 21 ]. The Distributed Temperature Sensing (DTS) technique [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ] is based on the Optical Time Domain Reflectometry (OTDR) concept [ 29 , 30 , 31 , 32 ]. This technique uses the optical fiber as the sensing element, with the intensity of the Raman back-scattered light of a laser pulse as a temperature dependent parameter.…”