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.

An optical spectrometer and/or a method of optical spectroscopy is described herein. One exemplary spectrometer includes a planar spectral filter, a dispersion system, and a detector array having at least two dimensions. The planar spectral filter filters incident light to generate a plurality of wavelength dependent spatial patterns. The dispersion system disperses the spatial patterns along at least one dimension in a wavelength dependent fashion onto the detector array. As a result, spatial patterns corresponding to different wavelengths are centered at different locations on the detector array. The dispersed spatial patterns superimpose at the detector array in an offset but overlapping relationship, creating an asymmetric image that facilitates the spectral analysis of a wide range of light sources, including diffuse or spectrally complex light sources.