Gas analyzers for geological applications
The ERC Project CO2Volc (responsible Dr. Mike Burton, INGV Pisa), aims to the study of the gaseous volcanic emissions, and in particular carbon dioxide, sulphur dioxide, hydrogen fluoride, hydrogen chloride and, for the first time, of the isotopic ratio of HCl.
Within this Project the SPHERES Group cooperates to the development, realization and field test of three point analyzers.
The first one measures the concentration of HCl and the isotopic ratio H<sup>37</sup>Cl/H<sup>35</sup>Cl. It is based on the measurement of the absorption of a molecular transition for each isotopologue, by means of two “Interband Cascade Lasers” (ICLs) in the medium infrared. The two laser beams are made collinear, and then interact with the atmosphere along an optical path of about 20 meters. This path is obtained with a multipass Herriott cell, developed specifically for this project, made with quarts, carbon fibers and stainless steel.
The second analyzer measures the concentrations of HF and CO<sub>2</sub>, and is based on two near infrared tunable diode lasers. The two lasers are fiber coupled, just like the reference cell for HF. The structure of the device is the same of the previous one.
The third instrument measures the concentration of SO<sub>2</sub>, and is based on an UV, fibere coupled LED. The structure is similar to those of the other two devices, but the coating of the mirrors of its multipass cell is dicroic (300 e 630 nm). Thi is to allow both the normal operation and the alignment with a HeNe laser. The detection is obtained by using a fiber coupled spectrometer.
Several test campaigns have been carried out on Etna, Vulcano and Stromboli, both on the ground and on board of an airplane and a helicopter.
In september 2016 a measurement campaign was carried out about a group of volcans in Indonesia, whose data are under analysis.
An instrument to be installed aboard a drone has been realized, which measures the same gases, though with reduced sensitivity, with a total weight of 3 kg. This device has been tested in 2017 on Vulcano and Etna mountains. Project ended on Dec. 31, 2017, but a further version of the drone-borne analyser is in progress. In this version all the sensitivities but that for HCl will be restored to the values of the “heavy” analysers.