[daip] Blanking of cubes

[Lincoln Greenhill]

Dear Leonia,

Your interest in developing this capability in AIPS
is extremely good news.  I know that manpower is limited.
(BTW - I still remember that I must followup on a previous
unrelated gripe by making available a dataset for you to run tests.)

After you have had time to think about possible algorithms, I
look forward to learning what your approach is.  Myself, I do
not know how to make it computationally efficient.

Regards,

Lincoln

On Wed, 7 Nov 2001, Leonia Kogan wrote:

> Hi Lincoln,
>
> I start working on the route 1 of your suggestion. I think I understand
> what shoud be done at least at the route 1. Having made a progress I'll
> ask you questions.
>
> I take the day off this Friday and I do not know yet how complicate is
> the job.  So I can not say when I finish.
>
>
> Leonia
>
>
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> Dear AIPSgroup,
>
> In projects BG98 and BG118 we are mapping the distribution of
> SiO maser emission on Orion BN/KL.  The distribution of emission
> is extremely complex, even in individual spectral channels, with
> dozens of detectable maser spots with a range of brightness of perhaps
> 1000.  Some channels do not clean well, because of extended flux that
> is not well sampled by the VLBA/Y1 array.
>
> When we apply XMOM to create moment maps that are intended to show the
> complex structure including weak maser emission, the poorly cleaned
> channels leave behind artifacts that reflect the beam response.  However,
> because the source is near 0 declination, the problem is localized to a
> roughly N-S band on the sky centered around bright maser components.
>
> We would like to be able to search the cubes, and blank emission based on
> a more complex rule set than is possible with XMOM.  I can think of
> two routes -
>
> 1) In XMOM, apply a cutoff based on a local calculation of signal-free RMS
> in each image plane - rather than only an absolute flux cutoff.  The size
> of the region (e.g. a square) over which the RMS is computed is provided
> by the user.
>
>
> 2) in BLANK or XMOM, apply an absolute flux cutoff (as is done now) and
> further clipping based on an input maximum acceptable dynamic range for
> a generic 2-D region around each strong emission features in each plane.
> The generic region shape is defined by the user; the program overlays
> it on each strong feature and blanks regions where emission is too weak.
>
>
> Has this problem been introduced by other AIPS users?  Can you think of
> other solutions to it?  Does the AIPS group see any general value in
> implementing a more sophisticated blanking algorithm than is available
> in XMOM/BLANK?
>
> Regards,
>
> Lincoln
>
>
>
>
> Lincoln J. Greenhill      Harvard-Smithsonian Center for Astrophysics
> Radio & Geoastronomy Division, 60 Garden St, Cambridge, MA 02138, USA
> Telephone:  1 617-495-7194             FAX:  1 617-495-7345
> Internet:  greenhill at cfa.harvard.edu   http://cfa-www.harvard.edu/~lincoln
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