J-band lights off sequence, 4 detectors shown
J-band lights on sequence, 4 detectors shown
(Lights on - lights off) averages, 4 detectors shown
Using linearity test data taken by Gonzalez et al. on 22 November 2007 (thanks to Adam Stanford for the logs).
Linearity observing sequence (first with lights on, then repeated with lights off):
J 6 x 1.238s J 6 x 10s J 6 x 2s J 4 x 12s J 6 x 3s J 4 x 14s J 6 x 4s J 4 x 16s J 6 x 5s J 4 x 18s J 6 x 6s J 4 x 20s J 6 x 7s (8 x 7s for the lights off sequence) J 4 x 22s J 6 x 8s J 4 x 24s J 6 x 9s J 4 x 26s J 4 x 28s J 4 x 30s J 4 x 35s J 4 x 40s J 4 x 45s J 4 x 50s J 4 x 55s J 4 x 60s H 1 x 2s J 1 x 10s
Between lights on and off:
Dark 10 x 1.238s
The following analysis considers mean behavior over each of the four NEWFIRM arrays, and is based on sigma-clipped averages computed for each of the four detectors. Pixel-to-pixel analysis will follow.
The first plots showing the detailed behavior (frame by frame) of the count rates for the lights off and lights on sequences. Blue points are the groups of short exposures (t=1.238, 2, 3, ..., 7, 8, 9 seconds) that were interleaved with the longer exposures.
The higher count rates for the shorter exposures in the lights-on and difference (on-off) sequences in part reflects the fact that they have lower total count levels and are thus more linear (i.e., higher count rates). However, other effects may be at work as well; note that the last short (blue) data set (t=9s) has a substantially higher count rate than the first long (red) data set (t=10s). Various effects might be at work, including persistence, array self heating, possible trends within the dome flat brightness, etc. Note that there are also trends within each set of exposures, especially for the lights-on sequences, suggesting transient behavior when the exposure time and/or the total count level changes suddenly.
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J-band lights off sequence, 4 detectors shown
J-band lights on sequence, 4 detectors shown | |
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(Lights on - lights off) averages, 4 detectors shown |
The next group of plots show the general trends vs. exposure time and count level for the four arrays. The last figure shows the linearity behavior schematically, where I have fit a line to the behavior of the count rate vs. counts data from exposures with 10 <= t <= 30 seconds, then normalizing the relative count rates from all data to the intercept of that line at n=0 counts (i.e., defining the data to be exactly linear at zero count level). The deviation of the (interleaved) short exposure (t <= 9s) points is clearly visible. The longer exposure times (t > 30s, counts > 7000s or so) systemtically depart from the linear fit, implying saturating linearity behavior, although in detail there seems to be a somewhat suspicious (but small) discontinuity between the behavior at t <= 30s and t >= 35s.
Counts vs. exposure time |
Count rate vs. exposure time |
Count rate vs. counts |
Relative nonlinearity. Linear fit (slope = s, intercept = 1) to data from 10s <= t <= 30s |