A comparison of reflected and emitted radiometric signal levels in SWIR, eSWIR, MWIR, and superband (SWIR through MWIR) optical systems

With the improvement of infrared detector technology over the last several decades, traditional design trades regarding the use of different wavebands in optical systems are becoming less and less applicable. New detector technology is allowing for extended and even bridged wavebands, where previous detectors were limited to only a single waveband. These bridged waveband cameras, or superband cameras, contain detectors with response over large spectral spans, allowing them to take advantage of the unique properties of multiple wavebands. This type of system is especially of interest when the superband contains both the short-wave infrared (SWIR) waveband – where most of the signal comes from reflected light – and midwave infrared (MWIR) waveband – where most of the signal comes from emitted light. Such a superband system allows the combination of reflected and emitted light on a single detector, opening new system level optical design trades across many fields and disciplines. Presented is a comparison of reflected and emitted radiometric signal levels for four filtered wavebands using a 1.5 μm to 5.4 μm superband imaging system: (1) with a 1.9 μm SWIR shortpass filter, (2) with a 2 μm to 2.5 μm extended SWIR (eSWIR) bandpass filter, (3) with a 3 μm MWIR longpass filter, and (4) with no filter (i.e., full superband response). The comparison in each of the four wavebands is repeated under four solar illumination conditions: full daylight, clouds, dusk, and night.