A gas filter correlation radiometry (GFCR) system, comprising:
- an optical train having an entrance aperture, said optical train adapted to receive light from a scene of interest at said entrance aperture, said optical train (i) using the light to form an image of the scene at a focal plane within said optical train, (ii) confining light from a selected field-of-view of the image at said focal plane to a spectral band at which a gas of interest absorbs, and (iii) splitting the confined light into first and second paths;
- a region that is substantially non-interfering with respect to said spectral band, said region being disposed along said first path;
- a first optical detector defined by a two-dimensional array of optical detection elements disposed in said region;
- a first diffuser disposed in said region at a position that is optically in front of said first optical detector, said first diffuser assuring that each portion of the confined light from said selected field-of-view of the image is identically distributed across at least a portion of said optical detection elements of said first optical detector wherein each of said optical detection elements of said first optical detector generates an output signal;
- a gas cell filled with the gas of interest, said gas cell disposed along said second path and permitting the confined light from said selected field-of-view of the image to pass therethrough;
- a second optical detector defined by a two-dimensional array of optical detection elements;
- a second diffuser disposed at a position that is optically between said gas cell and said second optical detector, said second diffuser assuring that each portion of the confined light from said selected field-of-view of the image is identically distributed across at least a portion of said optical detection elements of said second optical detector wherein each of said optical detection elements of said second optical detector generates an output signal;
- and
- processing means coupled to said first and second optical detectors for (i) summing said output signals generated by said first optical detector to form a first sum, (ii) summing said output signals generated by said second optical detector to form a second sum, (iii) generating a difference between said first and second sums, and (iv) normalizing said difference using at least one of said first and second sums.