Why take SCUBA noise measurements?
In most cases the first thing to check, once the TCS and SCUBA software is up and running, is that SCUBA is performing well. This is done in the first instance by the NOISE observation. The observation definition file is called noise_ref.obs (usually it is contained in the startup.m macro) and measures the “system” noise for each pixel looking at a cold load (actually a reflecting mirror in front of the cryostat window). Removing the mirror allows the “sky” noise level to be measured (noise_sky.obs) which is useful indicator of the stability of observing conditions. The rest of this report is mainly concerned with the interpretation of system noise data, and how to diagnose problems when excess noise levels are encountered. 2. Interpreting noise observations A noise observation will display the rms noise levels for each pixel after 64 seconds of integration time. The on-line display takes the form of a plot of noise voltage on the y-axis against pixel number on the x-axis. Since this d
