Search

This paper describes the design of a deep-UV Raman imaging spectrometer operating with an excitation wavelength of 228 nm. The designed system will provide the ability to detect explosives (both traditional military explosives and home-made explosives) from standoff distances of 1-10 meters with an interrogation area of 1 mm x 1 mm to 200 mm x 200 mm. This excitation wavelength provides resonant enhancement of many common explosives, no background fluorescence, and an enhanced cross-section due to the inverse wavelength scaling of Raman scattering. A coded-aperture spectrograph combined with compressive imaging algorithms will allow for wide-area interrogation with fast acquisition rates. Coded-aperture spectral imaging exploits the compressibility of hyperspectral data-cubes to greatly reduce the amount of acquired data needed to interrogate an area. The resultant systems are able to cover wider areas much faster than traditional push-broom and tunable filter systems. The full system design will be presented along with initial data from the instrument. Estimates for area scanning rates and chemical sensitivity will be presented. The system components include a solid-state deep-UV laser operating at 228 nm, a spectrograph consisting of well-corrected refractive imaging optics and a reflective grating, an intensified solar-blind CCD camera, and a high-efficiency collection optic.

The Visible Infrared Imager Radiometer Suite (VIIRS) is successfully operating on the Suomi National Polar-orbiting Partnership (NPP) observatory, launched on October 28, 2011. Numerous components of the prelaunch test program for sensor bands centered below 1 m were dictated by the performance requirements for ocean-color (OC) retrievals; several of these characterization activities evolved from those for the legacy sensor, the Moderate Resolution Imaging Spectroradiometer (MODIS). Addition of the Traveling Spectral Radiance and Irradiance Responsivity Calibration Using Uniform Sources (TSIRCUS) laser-based test source provided superior characterization for spectral testing and for radiometric response knowledge. Analysis suggests that band-to-band radiometric uncertainty is well below 0.5% for the OC bands, and resolution of spectral characteristics are known to better than 0.1 nm. The expected improvements in VIIRS performance testing from using T-SIRCUS and some benefits that accrue from these tests are reviewed.