Infrared hyperspectral imaging Fourier transform and dispersive spectrometers: comparison of signal-to-noise-based performance

Abstract

We compare the signal-to-noise ratio (SNR) based performance of scanning dispersive and staring (Michelson interferometer based) Fourier transform spectrometer approaches to hyperspectral infrared imaging. The information collected by the focal planes of these two spectrometer types is very different. In the scanning dispersive spectrometer, the 2-D focal plane array (FPA) collects spatial information in one direction and spectral information in the other, while the second spatial dimension is swept out in time by the scanning mechanism. The Fourier transform spectrometer 2-D focal plane array acquires 2-D spatial information while the spectrum (interferogram) is swept out in time. The formation of the signal and propagation of noise from the focal plane data collection to the final hyperspectral data cube are significantly different for each type of instrument, and distinct signal and noise models apply to each. Using the noise equivalent spectral radiance (NESR)as a figure of merit, we compare the performance of the two types of instrument with the same optical system, equal spatial resolution, image area, spectral resolution, spectral span, and imaging time. Under photon noise limited conditions (for each instrument), which are made possible by the proper design of modern infrared focal plane arrays, the traditional multiplex (Fellgett) and throughput (Jacquinot) advantages associated with non-imaging Fourier transform spectrometers vanish for reasons that will be made clear in the paper. We discuss 2-D focal plane array characteristics for each instrument, such as frame rate, dynamic range, etc. and show why they are so different (by design) between these two instruments. Finally, the consequences of the signal processing requirements implied by the two instruments are summarized.