[alma-config] (no subject)

[Al Wootten]

Gosh Frederic et al

This discussion has reawakened long dormant sections of my brain; I
certainly didn't mean to cut off discussion, only to clarify the
status of the configuration.  I hope that the last email is posted
only when the subject is exhausted.  Listeners, when exhausted, can
just press the delete key.

Cieux clairs,
Al  
Frederic Boone writes:
 > Hi John,
 > 
 > Following Al's email and as I promised I will not
 > discuss the design anymore. 
 > I also swear this is my last email ever to this list.
 > 
 > > The
 > > only (slightly, for radio astromomy) novel aspect of
 > > what I did was
 > > explicity to choose weights for each uv point in a
 > > snapshot to
 > > force explicity the beam to a  gaussian shape.
 > 
 > This is precisly the problem: this is not novel, this
 > was done in memo 400 ("compensate the density excess
 > with respect to an ideal distribution"). 
 > 
 > I don't pretend I invented "weights".
 > My only contribution at this level was to propose
 > weights could be used to force the beam to have a
 > given shape. You can say your formulation (i.e. the
 > words used and how this is achieved) is different than
 > mine but the idea is exactly the same.
 > 
 > > Most implementations of beam forcing in radio
 > astronomy,
 > > generally force
 > > uniform uv density on a grid, then gaussian taper
 > the result (this is
 > > I think what is described in memo 400)
 > 
 > First I don't know any reference mentioning this (I
 > would be interested to know about all these very
 > numerous references you imply with "Most
 > implementations"). As far as I know radioastronomers
 > use uniform weighting to gain in resolution and
 > tapering to increase the brightness sensitivity but I
 > don't know any example where both are used together.
 > 
 > Second, this cannot work efficiently because to force
 > the shape of the beam it is required to get a sense of
 > the actual distribution of weights in the data and
 > this is very difficult with the gridding used in the
 > method you mention (it requires super-Nyquist sampling
 > everywhere to be really efficient).
 > 
 > I have to acknowledge the appendix of the memo was not
 > complete enough, and I always thought I should write a
 > memo to describe the method used in more detail (I am
 > still planing to do this and you give me more
 > motivation now). I gave only few more hints (but still
 > not enough details) in my thesis manuscript (online on
 > my web page, p39, sorry this is in french).
 > 
 > Regards,
 > Frederic
 > 
 > 
 > 
 > 
 > 	
 > 
 > 	
 > 		
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