Table 1
CCD performance in terms of the video-chain total detection noise as measured from the second of the two prescan samples available for each CCD, but summarised via a mean and standard deviation over all CCDs grouped by instrument.
| Instrument | Mean gain | Total detection noise per sample | ||
|---|---|---|---|---|
| and mode | ADU/e− | Required/e− | Measured/e− | Measured/ADU |
| SM | 0.2569 | 13.0 | 10.829 ± 0.494 | 2.782 ± 0.127 |
| AF1 | 0.2583 | 10.0 | 8.556 ± 0.438 | 2.210 ± 0.113 |
| AF2–9 | 0.2578 | 6.5 | 4.326 ± 0.648 | 1.115 ± 0.167 |
| BP | 0.2464 | 6.5 | 5.170 ± 0.362 | 1.274 ± 0.089 |
| RP | 0.2484 | 6.5 | 4.752 ± 0.175 | 1.180 ± 0.043 |
| RVS-HR | 1.7700 | 6.0 | 3.272 ± 0.155 | 5.791 ± 0.274 |
| RVS-LR | 1.8185 | 4.0 | 2.907 ± 0.177 | 5.286 ± 0.322 |
Notes. The analysis period used was July 2014 to November 2016 and covers the entire science operational period of DR2. Measurements are given in analogue-to-digital units (ADU) and electrons using the gain measurements quoted in the second column, where the gain was measured on-ground prior to launch (this cannot be measured in-orbit owing to the non-availability of flat field illumination). All instruments are statistically well within the design requirement quoted in the third column. For the RVS instrument, the measurements are subdivided into high-resolution (HR) and low-resolution (LR) modes where the latter samples are hardware binned on-chip by 3 pixels in the along-scan direction. This observing mode was used only briefly at the start of the mission (Cropper et al. 2018). Note the larger gain in the RVS: this is the main contributor to the greater impact of the bias non-uniformity in this instrument.