The SWAP EUV Imaging Telescope. Part II: In-flight Performance and Calibration


The Sun Watcher with Active Pixel System detector and Image Processing (SWAP) telescope was launched on 2 November 2009 onboard the ESA PROBA2 technological mission and has acquired images of the solar corona every one to two minutes for more than two years. The most important technological developments included in SWAP are a radiation-resistant CMOS-APS detector and a novel onboard data-prioritization scheme. Although such detectors have been used previously in space, they have never been used for long-term scientific observations on orbit. Thus SWAP requires a careful calibration to guarantee the science return of the instrument. Since launch we have regularly monitored the evolution of SWAP’s detector response in-flight to characterize both its performance and degradation over the course of the mission. These measurements are also used to reduce detector noise in calibrated images (by subtracting dark-current). Because accurate measurements of detector dark-current require large telescope off-points, we also monitored straylight levels in the instrument to ensure that these calibration measurements are not contaminated by residual signal from the Sun. Here we present the results of these tests and examine the variation of instrumental response and noise as a function of both time and temperature throughout the mission.

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    Owing to in-flight image-sequence constraints, the images at 70 arcmin were captured after the instrument was pointed back to the Sun for a short duration. Therefore they are perturbed by a remnant image of the Sun most probably caused by the detector scintillator coating behavior (De Groof et al. 2008).


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The SWAP instrument was developed by Centre Spatial de Liège (University of Liège) in collaboration with the Royal Observatory of Belgium. Support for calibration was provided by the Max Planck Institute for Solar System Research. Belgian activities are funded by the Belgian Federal Science Policy Office (BELSPO), through the ESA/PRODEX program for the payload instruments, and the ESA/GSTP program for the PROBA2 platform. EVE data are courtesy of NASA/SDO and the EVE science team.

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Correspondence to J.-P. Halain.

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PROBA2 – First Two Years of Solar Observation

Guest Editors: David Berghmans, Anik De Groof, Marie Dominique, and Jean-François Hochedez

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Halain, J., Berghmans, D., Seaton, D.B. et al. The SWAP EUV Imaging Telescope. Part II: In-flight Performance and Calibration. Sol Phys 286, 67–91 (2013).

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  • Detector calibration
  • Dead pixel
  • Dark-current
  • Detector noise
  • Straylight