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Proceedings Paper

A hyperspectral imager for high radiometric accuracy Earth climate studies
Author(s): Joey Espejo; Ginger Drake; Karl Heuerman; Greg Kopp; Alex Lieber; Paul Smith; Bill Vermeer
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Paper Abstract

We demonstrate a visible and near-infrared prototype pushbroom hyperspectral imager for Earth climate studies that is capable of using direct solar viewing for on-orbit cross calibration and degradation tracking. Direct calibration to solar spectral irradiances allow the Earth-viewing instrument to achieve required climate-driven absolute radiometric accuracies of <0.2% (1σ). A solar calibration requires viewing scenes having radiances 105 higher than typical Earth scenes. To facilitate this calibration, the instrument features an attenuation system that uses an optimized combination of different precision aperture sizes, neutral density filters, and variable integration timing for Earth and solar viewing. The optical system consists of a three-mirror anastigmat telescope and an Offner spectrometer. The as-built system has a 12.2° cross track field of view with 3 arcmin spatial resolution and covers a 350-1050 nm spectral range with 10 nm resolution. A polarization compensated configuration using the Offner in an out of plane alignment is demonstrated as a viable approach to minimizing polarization sensitivity. The mechanical design takes advantage of relaxed tolerances in the optical design by using rigid, non-adjustable diamond-turned tabs for optical mount locating surfaces. We show that this approach achieves the required optical performance. A prototype spaceflight unit is also demonstrated to prove the applicability of these solar cross calibration methods to on-orbit environments. This unit is evaluated for optical performance prior to and after GEVS shake, thermal vacuum, and lifecycle tests.

Paper Details

Date Published: 6 September 2011
PDF: 10 pages
Proc. SPIE 8158, Imaging Spectrometry XVI, 81580B (6 September 2011); doi: 10.1117/12.893803
Show Author Affiliations
Joey Espejo, Univ. of Colorado at Boulder (United States)
Ginger Drake, Univ. of Colorado at Boulder (United States)
Karl Heuerman, Univ. of Colorado at Boulder (United States)
Greg Kopp, Univ. of Colorado at Boulder (United States)
Alex Lieber, Univ. of Colorado at Boulder (United States)
Paul Smith, Univ. of Colorado at Boulder (United States)
Bill Vermeer, Univ. of Colorado at Boulder (United States)

Published in SPIE Proceedings Vol. 8158:
Imaging Spectrometry XVI
Sylvia S. Shen; Paul E. Lewis, Editor(s)

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