The read noise (RON) is measured as rms in a single raw frame and in the master bias frame, using in both cases a small central window 100x100 pixels wide. The RON of the master bias frame is about a factor sqrt(N) lower than the raw file RON, where N typically is 5. RON is given in electrons, calculated from the ADU value using the nominal transformation factor (CONAD = 1/gain) 2.25 e-/ADU. (The measured CONAD values are close to that value, check out here.)
TITLE QC1 parameters TABLE_NAME qc1 TABLE_TYPE QC1_TABLE TABLE_ROW1 QC.OUT1.RON.RAW SEP giraffe_bias..sigma_raw TABLE_ROW2 QC.OUT1.RON.MASTER SEP giraffe_bias..sigma_master TITLE Algorithm The read noise (RON) is measured as rms in a single raw frame and in the master bias frame, using in both cases a small central window 100x100 pixels wide. Outliers below 100 and above 300 ADU are clipped. TITLE TrendingBox 2 of the trending plot shows the RON of single raw BIAS frames, box 3 the RON of master bias frames.
TABLE_NAME ron_plots TABLE_TYPE FIGURE_1A TABLE_WIDTH 80% TABLE_IMG1 AHREF="../img/trend_bias_box2.gif" TABLE_IMG1 "../img/trend_bias_box2.gif" border="1" width="253" height=125" TABLE_CAP1 RON plots. Box 2 shows the RON of single raw BIAS frames, box 3 the RON of master bias frames, typically constructed from 5 input raw frames. TITLE Scoring&thresholds The sigma_raw is tightly scored, with dynamic thresholds following the median average of the current period. The thresholds could be made even tighter but due to the relatively small window for the noise measurement the risk of false red scores due to outlier cosmics would then increase. The window size is chosen as to minimize the larger-scale structure of the bias.The sigma_raw is a KPI parameter, with its reference value being 4.2 el- (from the commissioning report of the new CCD), slightly higher than the current value. TITLE History The sigma_raw value is very stable over time.