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24 August 2005 Experimental and numerical optimization of a coronagraph external occulter. Application to SECCHI-COR2 and GOES-R SCOR
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The space-born coronagraph is an instrument used to observe the solar corona, the outer atmosphere of the Sun, typically over a range of altitudes from close to the limb of the solar disk to tens of solar radii. The brightness of the solar disk is many orders of magnitude greater than that of the corona. A coronagraph is designed to reject the light from the solar disk such that the corona is observable. An externally-occulted coronagraph is basically a telescope that forms an image of the corona, with the addition of an external occulter before and an internal occulter after the objective elements and stops, positioned and sized to reject light from the solar disk. The main source of stray light is diffraction of solar light around the edge of the external occulter, which is then scattered into the image plane by the optical elements. The occulters and stops are designed to reduce the intensity of diffracted and scattered light in the coronagraph as much as possible. We have developed a numerical model of the diffraction by an external occulter system and validated the model experimentally. We used the model to optimize the external occulter design for the SECCHI COR2 instrument, which is part of the NASA STEREO mission. We also used the model for the GOES-R SCOR concept design to predict the sensitivity of the instrument to misalignment and off-pointing from the Sun. In this paper, we will present the results of this experimental and numerical study of the performance of the external occulters on these instruments.
© (2005) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
A. Thernisien, R. C. Colaninno, S. Plunkett, D. G. Socker, Q. Gong, and F. Landini "Experimental and numerical optimization of a coronagraph external occulter. Application to SECCHI-COR2 and GOES-R SCOR", Proc. SPIE 5901, Solar Physics and Space Weather Instrumentation, 59011E (24 August 2005);


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