Shortwave Infrared for Night Vision Applications at Fraunhofer IOSB

Nightglow is an illumination phenomenon created by luminance processes in the higher earth atmosphere. It covers the spectral range from the ultraviolet up to the thermal infrared, but its maximum is found in the shortwave infrared (SWIR). Although known for a long time the advent of high sensitive SWIR detectors in the last decade enables today's use for night vision applications. In 2013 Fraunhofer IOSB started its assessment of SWIR for night vision applications. The approach was twofold. Continuous measurements were started to get an understanding of the highly variable illumination levels created by the nightglow under different environmental conditions. Future goal here is the standardization of the SWIR illumination levels corresponding to the defined visual full moon, quarter moon, starlight and overcast starlight ones. Additionally, performance assessment of SWIR detectors in comparison to the visual image intensifiers respectively low light focal plane array detectors were conducted in the laboratory as well as in the field. The paper gives history and status of IOSBs assessment of SWIR for night vision applications. It explains the ideas behind the illumination characterization, the conducted measurements and the inherent problem of artificial stray light. For sensor assessment it presents recent work on the influence of the spectral coverage (e.g. broadband versus atmospheric window only) on system performance for different environmental conditions.