24 October 2013 Stray light calibration of the Dawn Framing Camera
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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.
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Gabor Kovacs, Gabor Kovacs, Holger Sierks, Holger Sierks, Andreas Nathues, Andreas Nathues, Michael Richards, Michael Richards, Pablo Gutierrez-Marques, Pablo Gutierrez-Marques, } "Stray light calibration of the Dawn Framing Camera", Proc. SPIE 8889, Sensors, Systems, and Next-Generation Satellites XVII, 888912 (24 October 2013); doi: 10.1117/12.2030584; https://doi.org/10.1117/12.2030584
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