Thermal monitoring of active volcanoes has long been the domain of satellite and airborne remote sensing (for reviews of current capabilities, see Harris et al. ). However, ground-based thermal sensors offer considerable benefits in that (1) they can be located beneath cloud decks that prohibit aerial views; (2) they allow small thermal targets to be resolved; (3) they observe targets with a constant viewing geometry for long periods of time; and (4) they provide data at high sample rates (tens to hundreds of Hz). This latter capability is extremely attractive when tracking transient or rapidly evolving events, such as volcanic explosions. In addition, when used in conjunction with other geophysical data sets, thermal time series reveal clues as to the manner in which a volcanic system is erupting.