Apparatus and method for remotely detecting the presence of chemical warfare nerve agents in an air-released thermal cloud

A method for remotely detecting the presence of chemical warfare nerve agents in an air-released thermal cloud, comprising the steps of:

• aligning said thermal cloud within the field-of-view of an apparatus for remotely detecting the presence of chemical warfare nerve agents;
• collecting incident infrared radiation emitted by said thermal cloud;
• focusing the collected infrared radiation;
• selectively filtering the focused infrared radiation;
• detecting the selectively filtered infrared radiation;
• converting the detected infrared radiation into a plurality of thermograms;
• and
• comparatively analyzing the image contrast among said plurality of thermograms,
• whereby comparative analyses of the variations in image contrasts among said plurality of thermograms generated by sequentially filtering the infrared radiation emitted by said thermal cloud indicates the presence or absence of chemical warfare nerve agents in said thermal cloud.

In combination with a thermal viewer with an objective lens and a far infrared detector sensitive to a broad band of infrared frequencies, a subsystem for distinguishing one cloud of a first gaseous compound from an alternative cloud formed from a second gaseous compound when backlighted by a substantially uniform spectral distribution of light in the far infrared, comprising:

• a filter wheel mounted in said viewer between said objective lens and said detector having at least three apertures therein;
• one of said apertures being arranged to pass all far infrared frequencies in said broad band;
• each remaining aperture containing a filter which transmits only one of a group of different narrow bands of frequencies;
• and
• means mounted on said viewer to move said filter wheel so that said apertures are sequentially centered on the optical axis of said lens.