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High Spectral Resolution Longwave Infrared Hyperspectral Imaging System

Description:

TECHNOLOGY AREA(S): Sensors 

OBJECTIVE: Develop a high spectral resolution longwave infrared hyperspectral sensor suitable for low-to-medium altitude airborne intelligence, surveillance, and reconnaissance. 

DESCRIPTION: Airborne hyperspectral imaging (HSI) sensors have demonstrated utility for material detection and identification. Additionally, longwave infrared (LWIR) HSI systems can operate day/night and can be used to monitor gaseous effluents as many gases possess strong spectral features within the 7-14um spectral range. Existing dispersive systems demonstrate excellent radiometric performance but are generally limited in spectral resolution due to the relatively small format of available focal plane array (FPA) technology [1]. Fourier transform infrared (FTIR) systems can achieve high spectral resolution but at the expense of added collection time. For airborne platforms, this added time places too much demand on pointing and stabilization to prevent spectral artifacts. As next generation very longwave infrared (VLWIR) FPAs with small pitch, large format, and extended spectral range become available [2], next generation LWIR HSI sensors can potentially be developed capable of collecting with high spectral resolution while maintaining sufficient radiometric performance and collection time. This effort will produce a high spectral resolution LWIR HSI sensor with >400 (T) (500 (O)) bands over a spectral range of 8.0-12.5um (T) (8.0-13.0um (O)) with <12nm (T) (<10nm (O)) spectral resolution measured as full-width half max (FWHM). Additionally, the sensor must be able to collect a spatial scene of >400x400 pixels in <2s while maintaining a noise-equivalent spectral radiance (NESR) of < 2uW/(cm2-sr-um) (T) (< 1uW/(cm2-sr-um) (O)), while viewing a 300K blackbody source. Optical distortions, such as smile and keystone, will be maintained to <1/8 of a channel. 

PHASE I: This effort will develop candidate designs and evaluate available FPA technology. A full system model will be developed to determine expected performance of the system in terms of spectral sampling, spectral resolution (full-width half max), smile, keystone, and NESR for expected frame rate and exposure time of the system. 

PHASE II: The effort will refine the design as needed, procure materials and equipment, and build the system. The system will be fully characterized in a laboratory to measure spectral resolution, spectral smile, keystone, and spectral NESR. Additionally, tower testing of the instrument will occur with relevant field targets to demonstrate imaging performance and spectral exploitation. Government equipment and labs may be used in support of system testing and characterization. 

PHASE III: Phase 3 will refine the design based on outcomes of tests and customer feedback in Phase 2. The system will be flight tested and further integrated into a relevant pod given customer interest. 

REFERENCES: 

1. J. Hall, et al, “Mako airborne thermal infrared imaging spectrometer – performance update,” Proc. SPIE, 9976, 997604-1 – 997604-9, (2016); 2. H. Figgemeier, et al, “State of the Art of AIM LWIR and VLWIR MCT 2D Focal Plane Detector Arrays for Higher Operating Temperatures,” Proc. SPIE, 9819, 98191C-1 – 98191C-16, (2016)

KEYWORDS: Longwave Infrared, Hyperspectral Imaging, Sensor 

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