Lidar sounding of volcanic plumes

Abstract

Accurate knowledge of gas composition in volcanic plumes has high scientific and societal value. On the one hand, it gives information on the geophysical processes taking place inside volcanos; on the other hand, it provides alert on possible eruptions. For this reasons, it has been suggested to monitor volcanic plumes by lidar. In particular, one of the aims of the FP7 ERC project BRIDGE is the measurement of CO 2 concentration in volcanic gases by differential absorption lidar. This is a very challenging task due to the harsh environment, the narrowness and weakness of the CO 2 absorption lines and the difficulty to procure a suitable laser source. This paper, after a review on remote sensing of volcanic plumes, reports on the current progress of the lidar system.

The BrIdge voLcanic LIdar—BILLI: A Review of Data Collection and Processing Techniques in the Italian Most Hazardous Volcanic Areas

“…The transmission sub-system is based on a double grating dye-laser optically pumped by an injection seeded Nd:YAG laser (powerful, tunable and narrow-linewidth), a device for the frequency generation (i.e., difference frequency mixing, DFM), and an optical parametric amplifier operating in the NIR (Near IR) band (OPANIR). The limited tunability (few tenths of nm) of Tm, Ho:YLF, and fiber lasers was the main reason of their exclusion (from the transmission sub-system during the implementation stage) given the difficulties in choosing the best absorption line [36]. Instead, due to the harsh environment near degassing craters that can cause burns on the surface of nonlinear crystals, OPOs (optical parametric oscillators) have been discarded [37][38][39].…”

“…Instead, due to the harsh environment near degassing craters that can cause burns on the surface of nonlinear crystals, OPOs (optical parametric oscillators) have been discarded [37][38][39]. This transmitter was used to generate laser radiation at ≈2 µm, a region of the electromagnetic spectrum absorbed by atmospheric CO2, with negligible cross-sensitivity to H2O [36].…”

“…This transmitter was used to generate laser radiation at ≈2 µm, a region of the electromagnetic spectrum absorbed by atmospheric CO 2 , with negligible cross-sensitivity to H 2 O [36].…”

“…In order to fill these gaps, a new DIAL system, designed to measure the volcanic CO 2 flux, was developed as part of the ERC (European Research Council) Starting Grant Project "BRIDGE". The BrIdge voLcanic LIdar (BILLI), assembled at the ENEA (Italian National Agency for New Technologies, Energy and Sustainable Economic Development) Research Center of Frascati by the FSN-TECFIS-DIM group (Diagnostics and Metrology Laboratory) [36], successfully retrieved three-dimensional tomographies of volcanic CO 2 concentration in the plumes at Italy's most hazardous volcanic areas: Pozzuoli Solfatara (Naples, Italy) [21,37,38], the Stromboli volcano (Aeolians Islands, Italy) [39,40], and Mt. Etna (near Catania, Italy) [41,42].…”

Lidar detection of carbon dioxide in volcanic plumes

“…Carbon dioxide has been chosen because its anomalous release has been shown to anticipate volcanic eruptions 3 . Two systems are under development: BrIdge voLcanic LIdar (BILLI) 4 , funded by the ERC (European Research Council) project BRIDGE, and VULcamed Lidar (VULLI) funded by the ERDF (European Regional Development Fund) project VULCAMED. The first one is based on injection seeded Nd:YAG laser, double grating dye laser, difference frequency mixing (DFM) and optical parametric amplifier (OPA), and the second one relies on injection seeded Nd:YAG laser and optical parametric oscillator (OPO).…”