Open Path FT-IR Spectroscopy permits atmospheric measurements of compounds which absorb light at specific frequencies in IR range. In active configuration, the light source and the remote sensor are positioned at a distance of up to 500 m apart from each other.

All IR-active substances within this optical path can be detected. In this active configuration it is possible to carry out quantitative concentration measurements down to sub-ppb ranges. The passive configuration offers the advantage of beginning the measurement without any alignment of the IR. This passive configuration is not as sensitive as the active mode. However, the application of this passive configuration allows for successful large-area monitoring to be achieved.