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18 October 1996 Impact of the visible detector design on GOES imager and sounder MTF
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The modulation transfer function is one of the GOES Imager and Sounder system's key optical performance indicators. Though the visible images from GOES-8 and GOES-9 are excellent, the MTF values measured during ground tests are below expectations. The 4490 cycle per radian frequency MTF is particularly interesting because it is not significantly affected by small changes in focus or aberrations of the optical system. The primary contributors to the ow MTF values which are within the instrument are the ghost reflections from the transmissive components and the detector and its package. The ghost reflections that exist are certainly a factor in the stray light. An estimate of each ghost's intensity produces a worst case effect on MTF of approximately 2.5 percent. The detector itself appears to be the largest contributor to the stray light. There are several ways that the detector and its package contribute to the stray light. The most prominent among them is the reflection from the aluminum coated substrate combined with the closeness of the detector window. The stray light form the detector reduces the MTF by approximately 4 percent. Instantaneous geometric field of view (IGFOV) curves verify the existence of the stray light and calculations show approximately the magnitude of difference between measured and expected MTF data. A new detector design appropriate for the Imager visible channel or the Sounder star sense channel incorporates the changes recommended to reduce stray light within the detector THe first of the new detectors qualifies for the Sounder star sense detector. IGFOV curves show the reduction in stray light levels by about a factor of 2 to 4. Sounder star sense optical MTF data shows approximately 8 percent increase in the MTF at 4490 cycles per radian compared to SN05 Sounder.
© (1996) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Frederick L. Williams, David R. Wickholm, and John C. Ehlert "Impact of the visible detector design on GOES imager and sounder MTF", Proc. SPIE 2812, GOES-8 and Beyond, (18 October 1996);


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