- 22 Apr 2020
LMIRCam nightly darks
LMIRCam has in the past shown a variable read noise (pick-up noise). Operators should always keep an eye on LMIRCam read noise. At the beginning of each night, a few darks should be saved for monitoring and checked in real time to identify any issues that may have implications for what observations to prioritize throughout the night. High read noise can critically affect some observations while for others it may have negligible impact. The issue appears to have been fixed in summer 2019 by updating the grounding of the LBTI electronics. However, future instrument interventions may cause the problem to re-occur, so that monitoring is cirtical. If problems are found at the beginning of a night or even during the night, this can inform the prioritization of programs for the rest of the night and the near future.
- Type of observation: Closed dome, beginning of the night during startup.
- Duration: 5 min (data acquisition and real time check).
- Who: Science camera operator.
- Interval: Every night LBTI is on sky.
This data acquisition procedure assumes that the operator is able to perform basic LMIRCam imaging data acquisition.
- Insert Blank in LMIRCam FW4.
- Set PID to 19.
- Save 10 darks in full frame, minimum integration time in each readout mode (slow, medium, fast).
Analyzing distortion data
Search a clean area on the detector (few hot pixels), put an ROI there (stay within one channel, channel edges will mess up the measurement). Check the standard deviation within the ROI. The value should be around 2 counts for fast mode and around 40 counts in medium and slow mode.
- If noise is found to be high, execute observations that can accept the higher noise. High background (broad L or M filters) usually makes read noise negligible. ALES, JHK band, and narrow filter observations are more affected by read noise.
- It is possible that the noise is bad in one mode and good in another. Check all modes each time.