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| Joint Astronomy Centre |
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The single-moded optics allows hot-cold-sky calibration to be carried out using an external chopper wheel (in front of the dewar window) in the same manner as for heterodyne receivers. This is generally referred to as a Noise sky observation. A Noise reference observation is similar, but instead of looking at the sky the arrays look at a cold load provided by placing a reflector in front of the dewar window, and so effectively see themselves. Observations of science targets are interspersed with these observations to evaluate the performance of the bolometers. To evaluate the opacity along the line of sight, skydip observations are performed regularly. We also have a number of independent measuring devices for the opacity; these are described in depth on the Atmospheric calibration pages. Finally, SCUBA's gain sensitivity at any given time is estimated by observing either primary calibrators (the planets Mars, Uranus and Neptune) or secondary calibrators, to evaluate SCUBA's sensitivity. Information sensitivity calibration can be found from the Sensitivity calibration pages.
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