An update on SCUBA-2 commissioning

We’re well aware that it has been over a month since the last blog post, so it’s high time to post an update on SCUBA-2 commissioning. We had been investigating the mapping capabilities of the instrument in parallel with other instrument work, but now the emphasis and focus has shifted somewhat away from mapping and towards attaining an understanding of the sensitivity of the instrument. The arrays have been optimised for on-sky operations and we are shaking down the system to gauge the instrument’s point-source sensitivity.

Some of the activities that we have been working on since the last update include:

  • finalisation of array optimisation:
    • the best bias points for the heater and the superconducting arrays have been established
  • frame rate increase:
    • we investigated increasing the rate at which each data frame is read out, with a view to reducing the amount of noise aliased from higher frequencies; this gave us an improvement of about 20% in sensitivity at 850µm and 10% at 450µm (the latter, not as high as we had hoped or anticipated)
  • noise/NEP:
    • initial calculations seemed to imply that the dark NEPs were wildly varying and of course this caused a lot of concern. A lot of effort was invested in tracking this problem down and a couple of software bug fixes later, the calculated NEPs were seen to be actually stable over time (and always had been). This is clearly important as it allows us to establish by how much we are background limited
  • weather:
    • well, there’s not much we can do about the weather but it has hampered our on sky activities. The weather the last couple of months has been very poor, with even a snow storm in June which shut down the Mauna Kea summit for a weekend. We are now beginning to see changes in the forecast which we hope will bring better weather along, and more consistently so.
  • finding and fixing software bugs
    • and of course, we continue to exercise the software, finding and fixing bugs along the way.

We are now entering a crucial phase of the project, as we move towards determining the on-sky performance of SCUBA-2.

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