https://pfspipe.ipmu.jp/jira This file is an XML representation of an issue en-us 8.3.4 803005 13-09-2019 https://pfspipe.ipmu.jp/jira/browse/PIPE2D-1066 DRP 2-D Pipeline <p>The dot-roaching runs in 2022-06 showed that there is significant crosstalk between fibers, and gave preliminary coefficients (rhl has these). This needs to be accounted for in normal DRP processing.</p> PIPE2D-1066

Handle inter-fiber optical crosstalk.

Task Normal Done Done price cloomis EngRun Fri, 5 Aug 2022 14:07:41 +0000 Thu, 20 Oct 2022 18:58:08 +0000 Mon, 19 Sep 2022 22:47:23 +0000 0 4 <p>Actually, I measured the coefficients from a bright star &#8211; much more dynamic range. My notes say</p> <div class="code panel" style="border-width: 1px;"><div class="codeContent panelContent"> <pre class="code-java"> np.array([1.00000000e+00, 4.41695363e-03, 1.26907573e-03, 6.37238677e-04, 3.99808286e-04]) </pre> </div></div> <p>After some discussion, we decided that this should be done in 2-D.  One way would be to add these terms to the fibre profiles; another would be to <em>not</em> include them in the fibre profiles but to run a per-row correction just before writing the pfsArm files.</p> <p>In fact, of course, the cross-talk is 2-D, but we are planning to handle that by PFS subtraction in 2-D, including the far wings of the PSF, for lines that are bright enough to be a problem.   We do, naturally, have to be careful that we correct once and only once.</p> <p>Exactly what do the above coefficients represent, and how were they measured?</p> <p>I've an implementation that appears to work. I'd love to check it out on the original data used to measure the coefficients. <a href="https://pfspipe.ipmu.jp/jira/secure/ViewProfile.jspa?name=rhl" class="user-hover" rel="rhl">rhl</a>, do you have the visit number handy?</p> <p>Sorry, I should have included that information.  <tt>visit, arm = 78454, 'r'</tt>; <tt>fiberId = 586</tt></p> <p>Changes in code look fine with me. Minor comment on parameter doc. See pull request <a href="https://github.com/Subaru-PFS/drp_stella/pull/286" class="external-link" rel="nofollow">https://github.com/Subaru-PFS/drp_stella/pull/286</a>.</p> <p>The below plots show the spectra around <tt>fiberId=586</tt> before (dotted lines) and after (solid lines) the optical crosstalk correction. The first shows the full dynamic range. Note that the flux in the bright fiber is barely affected by the correction. The second shows a zoom around zero flux, where it can be seen the flux before correction is non-zero (especially for the two fibers closest to the bright one, blue and cyan), and that after correction it is much closer to zero.</p> <p><span class="image-wrap" style=""><img src="https://pfspipe.ipmu.jp/jira/secure/attachment/15330/15330_pipe2d-1066-bright.png" style="border: 0px solid black" /></span><br/> <span class="image-wrap" style=""><img src="https://pfspipe.ipmu.jp/jira/secure/attachment/15331/15331_pipe2d-1066-zoom.png" style="border: 0px solid black" /></span></p> <p>The "bright" fibre shouldn't be affected at all, should it, if there's no real flux in the neighbouring fibres?  How much is it modified?</p> <p>The bright fiber is barely modified (the difference is 0.05 +/- 0.11 counts).</p> <p>Merged to master.</p> <p>OK, now that "barely" means "not significantly" I'm happy.  I took it to mean a small but real shift (as e.g. you'd see if we did a naïve "1-loop" correction not a full matrix inversion.</p> <p>Oh, I should note a couple of things:</p> <p>1. The crosstalk correction needs to be activated explicitly (<tt>extractSpectra.doCrosstalk=True</tt>).<br/> 2. The overwhelming lack of reference points on <tt>visit=78454</tt> (which contains three traces and no emission lines) makes me wonder if the detectorMap adjustment in the spectral extraction used to measure the original crosstalk coefficients was reasonable. I have added a <tt>doForceTraces</tt> parameter to <tt>reduceExposure.py</tt> that forces use of traces (not just emission lines) when doing the detectorMap adjustment; this also needs to be activated explicitly.</p> Relates PIPE2D-1080 PIPE2D-1084 PIPE2D-1099 PIPE2D-1100 Development Rank 0|02qpio:k Reviewers hassan Sprint preEngRun07Sep Story Points 4.0