28 April 2009 Advanced pushbroom hyperspectral LWIR imagers
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Abstract
Performance studies and instrument designs for hyperspectral pushbroom imagers in thermal wavelength region are introduced. The studies involve imaging systems based on both MCT and microbolometer detector. All the systems employ pushbroom imaging spectrograph with transmission grating and on-axis optics. The aim of the work was to design high performance instruments with good image quality and compact size for various application requirements. A big challenge in realizing these goals without considerable cooling of the whole instrument is to control the instrument radiation from all the surfaces of the instrument itself. This challenge is even bigger in hyperspectral instruments, where the optical power from the target is spread spectrally over tens of pixels, but the instrument radiation is not dispersed. Without any suppression, the instrument radiation can overwhelm the radiation from the target by 1000 times. In the first imager design, BMC-technique (background monitoring on-chip), background suppression and temperature stabilization have been combined with cryo-cooled MCT-detector. The performance of a very compact hyperspectral imager with 84 spectral bands and 384 spatial samples has been studied and NESR of 18 mW/(m2srμm) at 10 μm wavelength for 300 K target has been achieved. This leads to SNR of 580. These results are based on a simulation model. The second version of the imager with an uncooled microbolometer detector and optics in ambient temperature aims at imaging targets at higher temperatures or with illumination. Heater rods with ellipsoidal reflectors can be used to illuminate the swath line of the hyperspectral imager on a target or sample, like drill core in mineralogical analysis. Performance characteristics for microbolometer version have been experimentally verified.
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Hannu Holma, Hannu Holma, Timo Hyvärinen, Timo Hyvärinen, Jarmo Lehtomaa, Jarmo Lehtomaa, Harri Karjalainen, Harri Karjalainen, Risto Jaskari, Risto Jaskari, } "Advanced pushbroom hyperspectral LWIR imagers", Proc. SPIE 7319, Next-Generation Spectroscopic Technologies II, 731907 (28 April 2009); doi: 10.1117/12.818557; https://doi.org/10.1117/12.818557
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