A hyperspectral imager for high radiometric accuracy Earth climate studies

Joey Espejo; Ginger Drake; Karl Heuerman; Greg Kopp; Alex Lieber; Paul Smith; Bill Vermeer

doi:10.1117/12.893803

6 September 2011 A hyperspectral imager for high radiometric accuracy Earth climate studies

Joey Espejo, Ginger Drake, Karl Heuerman, Greg Kopp, Alex Lieber, Paul Smith, Bill Vermeer

Proceedings Volume 8158, Imaging Spectrometry XVI; 81580B (2011) https://doi.org/10.1117/12.893803
Event: SPIE Optical Engineering + Applications, 2011, San Diego, California, United States

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.

Citation Download Citation

Joey Espejo, Ginger Drake, Karl Heuerman, Greg Kopp, Alex Lieber, Paul Smith, and Bill Vermeer "A hyperspectral imager for high radiometric accuracy Earth climate studies", Proc. SPIE 8158, Imaging Spectrometry XVI, 81580B (6 September 2011); https://doi.org/10.1117/12.893803

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