[alma-config] Fw: New results- have a look at this before the telecon, please.

[Steven]

I am not sure if this got through (I didn't receive a copy) so I am trying
another address...
----- Original Message -----
From: Steven <steven at heddle97.freeserve.co.uk>
To: <alma-config at planetas.aoc.nrao.edu>
Sent: Wednesday, August 23, 2000 9:26 AM
Subject: New results- have a look at this before the telecon, please.


> I have posted new simulations to my site, accessible as ever through the
> index page
> http://www.stevenheddle.co.uk/ALMA/ALMA_IND.HTM
> See the News section and the scetion at the bottom of the page.
>
> These simulations show CLEANed versions of the SIL imaged using A arrays
> at -23 declination. The dirty images have been redone for both the snaphot
> and tracks with an integration time of 14 seconds, which should sample at
> twice the Nyquist frequency for the long baselines. Difference images have
> also been calculated, by convolving the model images with the CLEAN beam
> used in the CLEANed images, then subtracting the scaled CLEAN image from
the
> convolved model using COMB. The scale factor employed is (peak flux in
> convolved model)/(peak flux in CLEANed image). However I now realise that
> this does not convey the dynamic range achieved by looking at the grey
scale
> and contour images alone- should I scale differently, or just post the
scale
> factors alongside the images. Also, for the A arrays the combination of
> images for differencing was straight forward as the CLEAN and model images
> were the same size and had the same pixel scale- scaling the image size
and
> translating looks like a thorny issue for the C and E arrays, but surely
> this is a familiar solved problem?
>
> The CLEANed and difference images presented have unfortunately had the
wrong
> CLEAN beam applied (the one relevant to the +25 dec rather than the -23
dec)
> due to a former bug in my CLEANing script, but I didn't have time to redo
> them for today, as even CLEANing to 5000 iterations takes 2.5 hours per
> image for the long tracks (about 4 minutes for the snapshots). Hopefully
> these results will still be useful as a marker for where we are at, and
form
> a basis for the agreed final deconvolution results. Some comparison
between
> the arrays may be possible using
> The amount of CLEANing is also less than I intended, with NITER=1000 for
the
> M51 results (also FACTOR=0.5, MINPATCH=256, PHAT=0.02, CLEAN box is whole
> image), with the other images having the same parameters except NITER=5000
> and MINPATCH=51. Time was the main constraint, and I had hoped a smaller
> MINPATCH might speed things up...not appreciably, I discovered.
>
> Remember, each image/array combination can have different CLEAN parameters
> (simply read from a file whose name is referenced in the setup file for
the
> script which writes the batch job) so any evolution of the parameters used
> is welcome- it would seem necessary for the MAR and MPD results presented.
>
> I have exported FITS images for the dirty beam, map, CLEAN beam and
> difference image of KACYG_4-23B7, but even gzipped they are nearly 4MB
each.
> I may get them uploaded later however- I'll send a message if successful.
>
> Speak to you later,
>     Cheers
>         Steven.
>
>