Comparing array performance : one year later

 

Power spectrum: RED = last year BLUE = current

As we prepare to complete the array characterisation phase of the commissioning programme, we can take stock of our current performance and compare to that prior to the start of S2SRO last year.

In all metrics that we use – pixel yield, NEP, stability – we have seen significant improvements. The figure above shows a comparison of some of these for the s4a array at 450µm: red lines are data from last year with more recent measurements as blue lines. The improvements are clear and we expect yet more improvement, especially at lower frequencies (important for mapping large scale structures), once we have optimised the performance of the NTD temperature controls.

The image below depicts a figure-of-merit that is used during commissioning to aid us in optimising the array set-up. Leaving the details aside, the improvement in performance we have seen in the 450µm array compared to last year is clear (results from the other two arrays, s4c and s4d, are faded out for clarity – there is no comparison to be made for these with last year).

Figure of Merit: TOP = current ; BOTTOM = last year

This is all very encouraging news and is a testament to the work carried out last Spring/Summer on the cold electronics modules (see their installation here). But, it must be stressed that this is performance in the dark and there is no guarantee that it will map directly onto on-sky performance. However, preliminary on-sky maps taken during recent functionality tests show a qualitative improvement in performance. This will be properly quantified within the next couple of months.

Advertisements

One Response to Comparing array performance : one year later

  1. Wrilliam says:

    Nice work on the noise level and 1/f.! Nominally, any drift in the drf base temperature is simply linear common mode. However, given that the base temperature may not be far lower than the transition temperature there may be some non-linear component to the gain changes with base temperature which will be more difficult to remove and produce artificial structure in a map.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: