6266428

Claims

• I claim: 1. A method of detecting and discriminating a hazardous cloud in a field of view, the method comprising: (a) forming a first linear discriminant for detecting the hazardous cloud at a first spectral resolution and forming a second linear discriminant for discriminating the hazardous cloud at a second spectral resolution which is higher than the first spectral resolution; (b) detecting the hazardous cloud by (i) taking a first .DELTA..sup.2 L spectrum in the field of view at the first spectral resolution, (ii) applying the first linear discriminant to the first .DELTA..sup.2 L spectrum to obtain a first response, and (iii) detecting whether the hazardous cloud is present in accordance with the first response; and (c) if the hazardous cloud is detected to be present in step (b)(iii), discriminating the hazardous cloud by (i) taking a second .DELTA..sup.2 L spectrum in the field of view at the second spectral resolution, (ii) applying the second linear discriminant to the second .DELTA..sup.2 L spectrum to obtain the second response; and (iii) discriminating the hazardous cloud in accordance with the second response. 2. The method of claim 1, wherein step (b)(iii) is performed automatically in a signal processing device. 3. The method of claim 2, wherein step (c)(iii) comprises: (A) forming an image of the second response; (B) displaying the image of the second response to an operator; and (C) receiving an input from the operator regarding the hazardous cloud. 4. A method of claim 1, wherein step (a) comprises forming the first and second linear discriminants from known spectral data for a plurality of materials by linear programming. 5. The method of claim 4, wherein step (a) comprises forming the first and second linear discriminants such that they give a non-zero response for a first of the plurality of materials and a substantially zero response for all of the plurality of materials except for the first of the plurality of materials. 6. The method of claim 1, wherein the first and second spectral resolutions are no higher than 16 cm.sup.-1. 7. The method of claim 6, wherein: the first spectral resolution is 64 cm.sup.-1 ; and the second spectral resolution is 16 cm.sup.-1. 8. The method of claim 1, wherein each of steps (b)(i) and (c)(i) comprises making a plurality of horizontal scans within the field of view, each of the horizontal scans at a different angle of elevation. 9. A system for detecting and discriminating a hazardous cloud in a field of view, the system comprising: detector means for (i) taking a first .DELTA..sup.2 L spectrum in the field of view at a first spectral resolution and (ii) taking a second .DELTA..sup.2 L spectrum in the field of view at a second spectral resolution which is higher than the first spectral resolution; signal processor means, said processor means storing a first linear discriminant for detecting the hazardous cloud at a first spectral resolution and a second linear discriminant for discriminating the hazardous cloud at a second spectral resolution which is higher than the first spectral resolution, for (i) detecting the hazardous cloud by applying the first linear discriminant to the first .DELTA..sup.2 L spectrum to obtain a first response and detecting whether the hazardous cloud is present in accordance with the first response and (ii) if the hazardous cloud is detected to be present, discriminating the hazardous cloud by applying the second linear discriminant to the second .DELTA..sup.2 L spectrum to obtain the second response and discriminating the hazardous cloud in accordance with the second response; and interface means for communicating to an operator a result of at least one of detecting and discriminating the hazardous cloud. 10. The system of claim 9, wherein: the signal processing means comprises means for forming an image of the second response; and the interface means comprises means for displaying the image of the second response to the operator under control of the signal processing means. 11. The system of claim 10, wherein the interface means further comprises means for receiving an input from the operator. 12. The system of claim 11, wherein the hazardous cloud is detected automatically in the signal processing means. 13. The system of claim 12, wherein the hazardous cloud is discriminated by displaying the image to the operator, allowing the operator to make the input indicating discrimination of the hazardous cloud, and receiving from the operator the input. 14. The system of claim 9, wherein the signal processing means comprises means for forming the first and second linear discriminants from known spectral data for a plurality of materials by linear programming. 15. The system of claim 14, wherein the means for forming forms the first and second linear discriminants such that they give a non-zero response for a first of the plurality of materials and a substantially zero response for all of the plurality of materials except for the first of the plurality of materials. 16. The system of claim 9, wherein the first and second spectral resolutions are no higher than 16 cm.sup.-1. 17. The system of claim 16, wherein: the first spectral resolution is 64 cm.sup.-1 ; and the second spectral resolution is 16 cm.sup.-1. 18. The system of claim 9, wherein the detecting means comprises means for taking each of the first and second .DELTA..sup.2 L spectra by making a plurality of horizontal scans within the field of view, each of the horizontal scans at a different angle of elevation. 19. The system of claim 18, wherein the means for taking comprises a horizontal scanning mirror and a vertical scanning mirror. 20. The system of claim 9, wherein the detecting means comprises an interferometer. 21. The system of claim 20, wherein the interferometer is a Michelson interferometer. 22. The system of claim 20, wherein the detecting means further comprises an array of at least two detector elements. 23. The system of claim 22, wherein the array comprises four detector elements.