24 September 2002 Improved wide-field collimator for dynamic testing of the GOES imager and sounder
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Abstract
The GOES Imager and Sounder instruments each observe the full Earth disk, 17.4° in diameter, from geostationary orbit. Pre-launch, each instrument's dynamic scanning performance is tested using the projection of a test pattern from a wide-field collimator. We are fabricating a second wide-field collimator (WFC2) to augment this test program. The WFC2 has several significant advantages over the existing WFC1. The WFC2 target illumination system uses an array of light-emitting diodes (LEDs) radiating at 680nm, which is within the visible bands of both the Imager and Sounder. The light from the LEDs is projected through a non-Lambertian diffuser plate and the target plate to the pupil of the projection lens. The WFC2's power dissipation is much lower than that of WFC1, decreasing stabilization time and eliminating the need for cooling fans. The WFC2's custom-designed 5-element projection lens has the same effective focal length (EFL) as the WFC1 projection lens. The WFC2 lens is optimized for the LED's narrow spectral band simplifying the design and improving image quality. The target plate is mounted in a frame with a mechanized micro-positioner system that controls three degrees of freedom: tip, tilt, and focus. The tip and tilt axes intersect in the WFC's image plane, and all adjustments are controlled remotely by the operator observing the target plate through an auto-collimating telescope.
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James C. Bremer, Shahriar Etemad, Barbara J. Zukowski, Bert A. Pasquale, Tmitri J. Zukowski, Robert E. Prince, Vincent Holmes, John A. Ryskewich, Patrick O'Neill, Jeanine E. Murphy-Morris, "Improved wide-field collimator for dynamic testing of the GOES imager and sounder", Proc. SPIE 4814, Earth Observing Systems VII, (24 September 2002); doi: 10.1117/12.451528; https://doi.org/10.1117/12.451528
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