Investigation of The Extended Shortwave Infrared (eSWIR) Band for Long-Range Object Discrimination and Other Applications

Abstract

The extended shortwave infrared (eSWIR) band from 2-2.5 μm has seldom been studied in depth for its impact on long-range imaging performance in comparison to the other reflective wavebands. The band itself, defined by a high atmospheric transmission window, has been known, however the technology to detect and image in the eSWIR band has only been made commercially-available in the last half decade. This work is an exploration of all aspects pertaining to the eSWIR band, with specific emphasis on its performance in long-range object discrimination. The research performed includes a quantitative comparison of eSWIR to the other reflective bands: visible, near infrared, and shortwave infrared, using a sensitivity- and resolution- matched experimental testbed. The design of such is explained in detail. To understand the various parameters associated with a passive imaging system, atmospheric transmission and solar irradiance are modeled in the relevant wavebands for a variety of visual environments and illumination conditions. Real sensor parameters are input into the Night Vision Integrated Performance Model to model theoretical system performance. Target reflectivity values are captured in the field and compared to calibrated targets of known spectral reflectivity. Passive imaging radiometry is demonstrated, and range performance models are matched with experimental imagery to provide an assessment of the signal-to-noise ratio, modulation transfer function, and contrast of targets at range in the field. The development of technology for commercially available eSWIR cameras made with mercury cadmium telluride and type-II superlattice focal plane arrays is advancing, and this work demonstrates system implementation of each type. In addition, there is a numerical comparison of detector size tradeoffs for the eSWIR band, with emphasis on illumination in passive imaging. The eSWIR band proves to be beneficial for long-range target acquisition because of its high atmospheric transmission and longer wavelength than the other reflective bands and has several other unique features, one being its emissive component counterpart. The output of this dissertation is a quantitative assessment of the benefits of eSWIR over the other reflective bands under a variety of conditions as well as a recommendation for optimal detector size for eSWIR cameras as they grow in their adoption.