[daip] AIPS handling of weights and flags

[Amy Mioduszewski]

Dear Eskil,

Our expert is away (back soon), but I will help you if I can.  Negative
weights mean that the visability is flagged.  I do not know if FIXWT
changes them, I suspect not.

SPLIT applies the flags (if you tell it to) and removes the FG table. 
Even if you set flagver -1 it will still not copy the flag table.  Also, I
think he negative visabilities will not be copied.

Amy

> Dear AIPS support,
> I wonder about how AIPS handles weights and flags. Please direct me to the
> appropriate place if this address is not the correct one. I've searched
> the
> net, cookbook and explain-pages without a clearcut answer. I would be very
> happy if someone could increase my knowledge around the following
> questions.
>
> What is the meaning of negative weights for visibilities? Is there a
> general way in which such visibilities are handled throught AIPS?
> Suppose that I modify weights on some visibilities using WTMOD (or
> ParselTongue) to -1. If I then use the task FIXWT to modify weights to
> reflect the amplitude scatter of data, will this also modify the negative
> weights? Or, will it only modify positive weights?
>
> Finally I wonder about SPLIT. SPLIT can apply an FG-table. If I make a
> single-source file using SPLIT from a multi-sourcefile, and chose to flag
> data using the multi-sourcefile-FG-table, will SPLIT remove every single
> flagged visibility? Or - since I don't see any FG table in the produced
> single-source file - are some visibilites still transferred for some
> reason
> but with modified weights? What about visibilites with negative weigths,
> will these count as flagged when using SPLIT?
>
> Best regards,
> Eskil Varenius
> PhD student
> Onsala Space Observatory
> Chalmers University of Technology
> Sweden
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