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

Claim 3

The invention as defined in claim 1 wherein: said selectively filtering means comprises a spectral filter wheel interposed between said focusing means and said detection means; said spectral filter wheel including a first spectral interference filter spectrally optimized to maximize the response of said apparatus to infrared radiation emission wavelength bands from approximately 8 microns to approximately 14 microns; a second spectral interference filter spectrally optimized to minimize the response of said apparatus to infrared radiation emission wavelength bands characteristic of chemical warfare nerve agents with respect to background infrared radiation; a third spectral interference filter spectrally optimized to maximize the response of said apparatus to a first major infrared radiation emission wavelength band characteristic of chemical warfare nerve agents; and a fourth spectral interference filter spectrally optimized to maximize the response of said apparatus to a second major infrared radiation emission wavelength band characteristic of chemical warfare nerve agents.

Claim 4

The invention as defined in claim 2 wherein: said second spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 10.25 microns to approximately 10.75 microns.

Claim 5

The invention as defined in claim 2 wherein: said third spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 9.60 microns to approximately 10.0 microns.

Claim 6

The invention as defined in claim 2 wherein: said fourth spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 10.7 microns to approximately 12.0 microns.

Claim 9

A method as described in claim 6 wherein the selective filtering of the focused infrared radiation further comprises the steps of: passing the focused infrared radiation through a first spectral interference filter, said first spectral interference filter being spectrally optimized to infrared radiation emission wavelength bands from approximately 8 microns to approximately 14 microns, to subsequently generate a first thermogram; passing the focused infrared radiation through a second spectral interference filter, said second spectral interference filter being spectrally optimized to minimize the response of said apparatus to infrared radiation emission wavelength bands characteristic of chemical warfare nerve agents with respect to background infrared radiation, to subsequently generate a second thermogram; passing the focused infrared radiation through a third spectral interference filter, said third spectral interference filter being spectrally optimized to maximize the response of said apparatus to a first major infrared radiation emission wavelength band characteristic of chemical warfare nerve agents, to subsequently generate a third thermogram; and passing the focused infrared radiation through a fourth spectral interference filter, said fourth spectral interference filter being spectrally optimized to maximize the response of said apparatus to a second major infrared radiation emission wavelength band characteristic of chemical warfare nerve agents, to subsequently generate a fourth thermogram.

Claim 10

A method as described in claim 7 wherein: said second spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 10.25 microns to approximately 10.75 microns.

Claim 11

A method as described in claim 7 wherein: said third spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 9.60 microns to approximately 10.0 microns.

Claim 12

A method as described in claim 7 wherein: said fourth spectral interference filter is spectrally optimized to pass infrared radiation having wavelengths from approximately 10.7 microns to approximately 12.0 microns.

Claim 13

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.

Claim 14

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.

Claim 15

An apparatus according to claim 11 wherein said wheel contains 4 apertures.

Claim 16

An apparatus according to claim 11 wherein: said filters consist of equal thickness plates of a material transparent to far infrared with at least one interference coating thereon.