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Proceedings Paper

Stray light calibration of the Dawn Framing Camera
Author(s): Gabor Kovacs; Holger Sierks; Andreas Nathues; Michael Richards; Pablo Gutierrez-Marques
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Paper Abstract

Sensitive imaging systems with high dynamic range onboard spacecrafts are susceptible to ghost and stray-light effects. During the design phase, the Dawn Framing Camera was laid out and optimized to minimize those unwanted, parasitic effects. However, the requirement of low distortion to the optical design and use of a front-lit focal plane array induced an additional stray light component. This paper presents the ground-based and in-flight procedures characterizing the stray-light artifacts. The in-flight test used the Sun as the stray light source, at different angles of incidence. The spacecraft was commanded to point predefined solar elongation positions, and long exposure images were recorded. The PSNIT function was calculated by the known illumination and the ground based calibration information. In the ground based calibration, several extended and point sources were used with long exposure times in dedicated imaging setups. The tests revealed that the major contribution to the stray light is coming from the ghost reflections between the focal plan array and the band pass interference filters. Various laboratory experiments and computer modeling simulations were carried out to quantify the amount of this effect, including the analysis of the diffractive reflection pattern generated by the imaging sensor. The accurate characterization of the detector reflection pattern is the key to successfully predict the intensity distribution of the ghost image. Based on the results, and the properties of the optical system, a novel correction method is applied in the image processing pipeline. The effect of this correction procedure is also demonstrated with the first images of asteroid Vesta.

Paper Details

Date Published: 24 October 2013
PDF: 8 pages
Proc. SPIE 8889, Sensors, Systems, and Next-Generation Satellites XVII, 888912 (24 October 2013); doi: 10.1117/12.2030584
Show Author Affiliations
Gabor Kovacs, Budapest Univ. of Technology (Hungary)
Holger Sierks, Max-Planck-Institut für Sonnensystemforschung (Germany)
Andreas Nathues, Max-Planck-Institut für Sonnensystemforschung (Germany)
Michael Richards, Max-Planck-Institut für Sonnensystemforschung (Germany)
Pablo Gutierrez-Marques, Max-Planck-Institut für Sonnensystemforschung (Germany)

Published in SPIE Proceedings Vol. 8889:
Sensors, Systems, and Next-Generation Satellites XVII
Roland Meynart; Steven P. Neeck; Haruhisa Shimoda, Editor(s)

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