Final answer:
FTIR is not used to monitor volcano deformation; it analyses gases. INSAR, tiltmeters, and GPS are used for measuring volcano deformation.
Step-by-step explanation:
The technique that is not used to monitor volcano deformation is FTIR (Fourier-Transform Infrared Spectroscopy). This method is primarily used to analyse gases released by a volcano, rather than to measure its deformation. In contrast, the other techniques mentioned are directly used for monitoring changes in the shape or position of a volcano's surface, which can indicate volcanic activity.
INSAR (Interferometric Synthetic Aperture Radar) uses radar to create detailed maps of deformation. Tiltmeters measure very small changes in angle and can detect volcanic swelling. GPS (Global Positioning System) is used for precise measurement of surface displacement.