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

Abstract

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 -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 darkcurrent). Since accurate measurements of detector dark-current require large telescope off-points, we have 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.

Degradation assessment of LYRA after 5 years on orbit - Technology Demonstration -

“…After almost 5 years in orbit, the 8 VFCs show good stability with time the spatial resolution of SWAP on PROBA2 complements well the high temporal resolution of the EUV LYRA channels [23]. SWAP-the Sun Watcher using APS and image Processing-is an EUV solar telescope centered at 17.4 nm and the first on orbit that benefits from CMOS Active Pixel Sensor technology [24,25]. The long-term variations of the EUV irradiance measured by LYRA are also compared with the EUV Variability Experiment (EVE) on board the Solar Dynamics Observatory (SDO) satellite [26].…”

The SWAP EUV Imaging Telescope Part I: Instrument Overview and Pre-Flight Testing

“…A careful analysis of the response, including cross-calibration with spectral observations from the EUV Variability Experiment (EVE) on SDO discussed in Halain et al (2012), revealed that because of shadowing due to the beam position with respect to the filter gridswhich can modulate the beam strength by nearly 20 % -the response function required a correction of about 12 %. (A complete discussion of the grid shadowing effect is included in Section 4.2.)…”

“…These routines are fully customizable via user-defined keywords and can be run on Level-0 images by users who require nonstandard calibration. Halain et al (2012) provide a detailed discussion of the measurement and evolution of pixel performance, dark current, and other important inputs into the calibration process for SWAP images.…”

SoFAST: Automated Flare Detection with the PROBA2/SWAP EUV Imager

“…SWAP onboard PROBA2 Halain et al, 2010Halain et al, , 2012Berghmans et al, 2006) is a small EUV imager, imaging the solar corona in a bandpass centred around 17.4 nm (174 Å). SWAP is a normal-incidence telescope in which the spectral selection is achieved by aluminium filters and multilayer coatings on the mirrors.…”