Furier Transform Infrared Spectrometry
FTIR is a Furier Transform Infrared Spectrometer that is used in volcanic hazards to measure and monitor gas emissions in fumeroles and clouds of active volcanoes. These measurements can help volcanologists determine what processes might be going on in the magma chamber under an active volcano, and what the volcano might do next.
The University of Cambridge is actively using the FTIR instrument in many studies, including this paper, Fourier transform spectroscopy of the gas plume of Masaya volcano, Nicaragua that gives an excellent description of the instrument and some uses for it. Dr Clive Oppenheimer runs many of the projects out of Cambridge on the instrument, and his web page offers FTIR information, along with other hazard assessment tools.
Another place to find useful information is the USGS website on FTIR. This description also includes some photos of the instrument itself.