Performance estimation for SWIR cameras under OH night airglow illumination

The authors estimate signal-to-noise ratios (SNRs) and contrasts for both InGaAs SWIR camera (cut-off wavelength λ co ~1.7 μm) and type II superlattice (T2SL) SWIR camera (λ co ~2.3 μm), under such situations as human skin as an object and vegetation as surroundings which are illuminated only by OH night airglow. In estimating the number of signal electrons, the measured spectral properties of quantum efficiencies for both InGaAs and T2SL detectors are used along with reflectance spectra of human skin and materials, while atmospheric transmission spectra are calculated with MODTRAN. As to noise electrons, shot noise resulting from dark current of InGaAs or T2SL detector is added to photon noise and ROIC (Read-Out Integrated Circuit) noise. The SNR values for the T2SL camera are found larger than those for the InGaAs camera. The contrasts of human skin vs surroundings are positive for the T2SL camera, while those for the InGaAs camera are negative.