[daip] forwarded message from Samuel Conner

[Eric Greisen]

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From: "Samuel Conner" <samuelconner at mail.arczip.com>
To: <egreisen at nrao.edu>
Subject: BLCAL feature wish and 2 questions
Date: Wed, 16 Feb 2005 12:58:07 -0700

Dear Dr. Greisen,
  
   Here are some features which might be useful in BLCAL. I've hacked it into an alternate (renamed) version of BLCAL on my local installation, and it seems to be helpful:

   a)  a SNR cutoff on |AMP - 1| below which (1,0) is written to the BL table. This is handy for doing early approximate corrections on a small set of baselines with unusually large offsets compared with the rest (this is a bigger problem in the archival observations I am working on than for modern ones, I'm sure)

   Something I haven't added yet but which might be useful is the ability to replace all solutions which have |AMP - 1| less than some value with (1,0), another way of getting at approximate early solution of large BL errors.


   b) Impose a UVRA outside of which data is not included in the solution (as in CALIB). If there is no data or too little for a high SNR solution, (1,0) goes into the BL table. This has seemed to be useful in high DR imaging in getting to a good model of diffuse emission in core-dominated sources which may be corrugated by the BL errors at longer spacings.

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Toward Question 1): I am slightly concerned about the way that BL and AN-based errors may interact in the CALIB and BLCAL process in extended sources. This is probably a subtle effect, if it is not entirely irrelevant (my intuition is not good on these matters). I'm thinking of trying to reduce to very high DR some archival full-aperture observations of radio galaxies for some simulations in which the improved DR might be useful.

The Question:  it seems to me that that the BL errors can bias the antenna solutions, particularly if one is not able to use the full UVRA in the early stages of self-calibration. Would it make sense to try to develop a model of the BL errors from suitable point source calibrators in the observation (if there are any) and apply these corrections to the data before self-calibration? Would it make sense to go back to the original Flux scale and phase calibration of the multi-source data and redo that with the BL corrections once these are derived? 


- ---

Question 2:  I am tempted to try to add some AIPS adverbs (a long linear array and a long text string, longer than the current adverbs) to improve the functionality of a VERB hack which I use to format and write numbers and text to disk text files. I have never added an adverb to the POPS environment and am intimated by the prospect.

Could you give me some quick quidance, or point to published resources which could guide me?

  Thanks for your time. I feel that I should send a gift to express my appreciation of your patience with me. Do you drink wine or champagne?

Sincerely yours,

Sam Conner

 
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