A correlation filter is provided having passbands at wavelengths corresponding to the absorption spectrum of an atmospheric gas of interest. In particular, the correlation filter features narrow, non-linearly spaced passbands having center wavelengths that are correlated to the non-linearly spaced absorption lines of an atmospheric gas. A correlation filter in accordance with an embodiment of the present invention includes a compensation stack having a number of thin film layers, at least some of which have an optical thickness that is not equal to an integer multiple of one-quarter of a wavelength of an absorption line of the gas of interest. The correlation filter may be provided in association with an etalon, or may comprise a number of optical cavities. In accordance with an embodiment of the present invention, a number of absorption lines associated with an atmospheric gas may be simultaneously viewed, providing a signal indicating the presence and quantity of such gas in the atmosphere having a high signal-to-noise ratio.
A method and apparatus for characterizing the spectral response function of hyperspectral electro-optical instruments or imaging spectrometers are provided. The system includes a test instrument that provides energy comprising multiple discrete wavelengths to the entrance slit of an instrument under test simultaneously. The provided energy can be scanned in the spectral dimension by changing the optical distance between the plates of a Fabry-Perot etalon incorporated into the test instrument. In addition, the energy provided to the instrument under test can be scanned in the spatial dimension by changing the location along the slit of the instrument under test at which the energy from the test instrument is provided.
A spectral correlator comprises a specimen and an optical device configured to collect light from the specimen and to optically determine a similarity of a received first spectra of the light collected from the first spectra and a second known spectra.
