Short scan passive infrared remote sensor

A short scan passive infrared remote sensor for detecting a target chemical species, located some distance from the center burst, includes a telescope for targeting a remote gas, a beam splitter means for splitting a beam from the target gas and sending one portion along a first path to an infrared detector and sending a second portion along a second path longer than the first path to the infrared detector. The second path is variable by providing a moving mirror a first distance away from the beam splitter which is 0.5 mm farther away from the beam splitter than the fixed mirror. By this arrangement, a mirror movement of only 0.5 mm is required to obtain an equivalent of 8 cm-1 spectral information for processing with time domain digital filters. The information from the infrared detector is converted from analog to digital and fed to a digital signal processor. The resulting interferogram is then filtered by a microprocessor using a FIR linear digital filter.