Divided-aperture infra-red spectral imaging system for chemical detection
A divided-aperture infrared spectral imaging (DAISI) system that is structured to provide identification of target chemical content in a single imaging shot based on spectrally-multiplexed operation. The system is devoid of spectral scanning acquisition of infrared (IR) spectral signatures of target content with an IR detector and does not require content.
1. An infrared (IR) imaging system comprising:
an optical system comprising an optical focal plane array (FPA) unit, wherein the optical FPA unit comprises at least one detector configured to measure a IR radiation spectrum from a corresponding optical channel; and
a processor in communication with the optical system and configured to:
determine a plurality of component spectra associated with the IR radiation spectrum,
estimate a plurality of weights corresponding to the plurality of component spectra, and
derive, based at least in part on the plurality of weights, a measurement spectrum.
2. The IR imaging system of claim 1 , wherein the plurality of component spectra corresponding to a plurality of absorption spectra of gases of interest.
3. The IR imaging system of claim 1 , wherein the measurement spectrum is associated with background light.
4. The IR imaging system of claim 1 , wherein the processor is configured to determine the plurality of component spectra based on a predetermined spectral library.
5. The IR imaging system of claim 1 , wherein the processor is configured to determine the plurality of component spectra based on an endmember determination algorithm.
6. The IR imaging system of claim 1 , wherein the optical FPA unit comprises at least two detectors, wherein the processor is configured to:
generate a spectral difference image by comparing images obtained by the at least two detectors, and
identify a target species based on the spectral difference image.
7. The IR imaging system of claim 1 , wherein the optical system defines at least two optical channels that are spatially and spectrally different from one another, wherein the processor is configured to:
generate a temporal difference reference based on a first plurality of images from the at least two optical channels; and
generate a temporal difference image based on the temporal difference reference and a difference between a second plurality of images obtained from the at least two optical channels at a later time.
8. The IR imaging system of claim 1 , wherein the processor is configured to acquire multispectral optical data representing a target species from IR radiation in a single occurrence of data acquisition.
9. The IR imaging system of claim 1 , wherein the processor is configured to generate an overall image data cube representing a spatial distribution of concentrations of a target species.
10. The IR imaging system of claim 1 further comprising a field reference positioned to obscure a peripheral region of a corresponding sub-image formed at the corresponding optical channel.
11. The IR imaging system of claim 10 , wherein the field reference defines an optical aperture that circumscribes the corresponding optical channel.
12. The IR imaging system of claim 11 , wherein the field reference is configured to have a uniform temperature across a surface of the field reference.
13. The IR imaging system of claim 1 further comprising a movable shutter configured to be removably positioned to block IR radiation onto the optical system.
14. The IR imaging system of claim 13 , wherein a first portion of the movable shutter is maintained at a first temperature and a second portion of the movable shutter is maintained at a second temperature.
15. The IR imaging system of claim 1 further comprising at least two optical filters that are spectrally-multiplexed and positioned to transmit a portion of IR radiation received in the corresponding optical channel.
16. The IR imaging system of claim 15 , wherein the at least two optical filters comprise at least one long-wavelength-pass optical filter.
17. The IR imaging system of claim 15 , wherein the at least two optical filters comprise at least one short-wavelength-pass optical filter.
18. The IR imaging system of claim 15 , wherein the at least two optical filters comprise both a long-wavelength-pass optical filter and a short-wavelength-pass optical filter.
19. The IR imaging system of claim 15 , wherein the at least two optical filters comprise a notch filter.
20. The IR imaging system of claim 15 further comprising a plurality of reimaging lenses, each of the plurality of reimaging lenses positioned to transmit IR radiation from the at least two optical filters towards the optical FPA unit.