Flagging and correction of pattern noise in the Kepler focal plane array

Abstract

In order for Kepler to achieve its required <20 PPM photometric precision for magnitude 12 and brighter stars, instrument-induced variations in the CCD readout bias pattern (our "2D black image"), which are either fixed or slowly varying in time, must be identified and the corresponding pixels either corrected or removed from further data processing. The two principle sources of these readout bias variations are crosstalk between the 84 science CCDs and the 4 fine guidance sensor (FGS) CCDs and a high frequency amplifier oscillation on <40% of the CCD readout channels. The crosstalk produces a synchronous pattern in the 2D black image with time-variation observed in <10% of individual pixel bias histories. We will describe a method of removing the crosstalk signal using continuously-collected data from masked and over-clocked image regions (our "collateral data"), and occasionally-collected full-frame images and reverse-clocked readout signals. We use this same set to detect regions affected by the oscillating amplifiers. The oscillations manifest as time-varying moiré pattern and rolling bands in the affected channels. Because this effect reduces the performance in only a small fraction of the array at any given time, we have developed an approach for flagging suspect data. The flags will provide the necessary means to resolve any potential ambiguity between instrument-induced variations and real photometric variations in a target time series. We will also evaluate the effectiveness of these techniques using flight data from background and selected target pixels.

KeplerData Validation I—Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates

“…10 A block diagram of the Pipeline is shown in Figure 1. Pixel level calibrations are performed in the Calibration (CAL) component (Quintana et al 2010;Clarke et al 2010Clarke et al , 2017a; late in the mission, a time-dependent two-dimensional bias correction was included with a new module named Dynablack (Kolodziejczak et al 2010;Clarke et al 2017b). Light curves are extracted by Simple Aperture Photometry (SAP) in the Photometric Analysis (PA) component (Twicken et al 2010a;Morris et al 2017) from pixels associated with each Kepler target star; the target photocenter (i.e., centroid position) is also computed for each target and cadence.…”

“…Rolling Band Artifact (RBA) metrics are produced in the Dynablack (Kolodziejczak et al 2010;Clarke et al 2017b) module of CAL by readout channel, CCD row, and cadence. The metrics are generated for a configurable set of pulse durations.…”

Kepler Science Operations Center architecture

“…The 2D Black and Artifact Removal Tool (BART) detects and models temperature-dependent image artifacts in pixel data 23 . The main purpose of BART is to support the decision to eject the spacecraft dust cover, during the commissioning phase of the mission.…”

When flux standards go wild: white dwarfs in the age of Kepler

“…However, flagging has been discontinued for K2(Van Cleve et al 2016). The three readout ports with the worst rolling band patterns are Channel 26 (Module 9.2), Channel 44 (Module 13.4), and Channel 58 (Module 17.2), although the artifact can affect more than 30 of the 84 science CCDs(Kolodziejczak et al 2010; G. Barentsen, private communication).MNRAS in press, 000-000(0000)…”