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

TL;DR

This paper details the in-flight performance, calibration, and degradation monitoring of the SWAP EUV solar telescope over two years, emphasizing detector response, noise reduction, and straylight levels.

Contribution

It provides a comprehensive calibration and performance analysis of the SWAP telescope's CMOS-APS detector during its mission.

Findings

Detector response evolved over time and temperature.

Calibration procedures effectively reduced detector noise.

Straylight levels remained controlled to ensure data quality.

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 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). 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.