High-frequency recording of the volcanic gas compositions using Open-path Fourier transform infrared (OP-FTIR) spectroscopy.

It allows determining at safe distance (< 1 km), at high frequency (1-5 Hz), with one single detector and accurately (+/- 4-10%) the overall composition (H2O, CO2, SO2, HCl, HF, CO, COS) of high-temperature gases issuing from craters and powering eruption columns. Moreover, both spectral recording in the thermal infrared and measurement of the CO/CO2 redox ratio permit us to infer the gas emission temperature.