Optical EngineeringCalibration and performance evaluation of a portable shortwave infrared (1.05- to 2.45-μm) spectrometer
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A portable shortwave infrared (SWIR) spectrometer has been developed that covers the range from 1.05 to 2.45 μm. The spectral sampling interval is 1.37 nm, and the spectral resolution can be varied from about 5 nm to more than 100 nm. A single spectrum can be acquired in as little as 1 s. The signal-to-noise ratio (SNR) for a single 1-s scan is about 100 at a wavelength of 2.2 μm for a lambertian surface of 100% reflectance illuminated by the sun at normal incidence with 14-nm spectral resolution. The SNR at 1.25 μm is about 900 for the same conditions. The estimated 1o uncertainty in the absolute radiometric calibration of the instrument is 2% to 3%. Field-of-view defining optics are coupled by a flexible fiber optic bundle to the spectrometer, which consists of a nonscanning concave holographic diffraction grating with a flat focal field imaged onto a 1024-element liquid nitrogen cooled PtSi linear array detector. The primary use for the instrument is the collection of ground reflectance and radiance data for the radiometric calibration of operational and proposed high spectral resolution remote sensing systems.