Quantification of poor extended imaging: flux in center of image for Gaussian sources as a function of source size. Proposed ES configuration is not as bad as SMA, but it has twice the number of antennas so should do be able to do better. It is clearly much worse than CARMA.

Dec 2010 compact.v2.cfg new config from Frederic, limiting baselines to 100m. The distribution of uv points still leaves a large inner hole, leaving doubts whether this is the best configuration for imaging extended structure.

Comparing new beams with previous Nov 2010 beams at dec=-20 and dec=-40, 6h tracks:

Analysis of Nov 2010 compact config Compact_16.cfg, constructed by Frederic Boone w/constraints of BL > 20m, using N half of the inner cluster: CSV-624

compact.plotants.pngESArray LegalPads.jpg

description of what he did is here: alma16ant.pdf
. Spreadsheet with antenna positions and baselines for the selected 16 and for all available antennas:
  • ES_Arrays.xls: Spreadsheet of antennas available, baselines, etc. Ignore rows 37-52, leftovers from previous spreadsheet.
I confirm that natural weighting produces the same beams as his "unweighted" in his document, and that the sidelobes are pretty high especially for a short (1h) observation:
Microsoft ExcelSnap001.png

There's not much shadowing - none in a 6h track at dec=-20, a little at dec +20 in a 6h track, mostly of the single antenna A015: (yes, I know plotms didn't reflect the uv points. deal. :)

a little at dec -80 in a 6h track, mostly of the single antenna A014:

I cannot reproduce Frederic's radial uv densities - I see a much narrower FWHM than in his document, unless he didn't divide by the geometric 1/r factor or something:
1mm.d-20.6h.uvdist.png 1mm.d-20.1h.uvdist.png
1mm.d20.6h.uvdist.png 1mm.d20.1h.uvdist.png

Next, I compare to CARMA


In general, their config is N/S elongated, so the beam is pretty noncircular at zenith, but its properties vary less dramatically with dec. The dec plotted for CARMA is (-23+37-(simulated dec)) to be compared with ALMA. CARMA's beam has a lower positive sidelobe, but a more negative bowl, so I don't know if I'd say one or the other is dramatically better, just different:
Microsoft ExcelSnap002.png

imaging an extended source:

CARMA (noiseless; log intensity scale):

ES ALMA (noiseless):

ES ALMA (noiseless, small mosaic):

ES ALMA with noise:

comparison of radial uv distribution. CARMA has been scaled to approximately the same max baseline as ALMA. es.carma.uvdists.png

contrast with FS configuration design philosophy:

The original design 2006-06-20-ALMA- had few constraints, and specified the shortest baseline:
SCIG-00060-00/R An antenna pad separation of 15.15m shall be possible.

For the compact array of 50 antennas, the configuration was sidelobe-optimized, in contrast to the Boone ES process: The positions of the ... 50 pads within the compact array were then optimized to give minimum sidelobes after multiplying the beam pattern with the autocorrelation of the primary beam (see Woody 2001, ALMA Memos 389 390). The sidelobe optimization used a modified version of the Kogan algorithm (see Kogan 1997, ALMA memo 171) . The algorithim was improved to minimize simultaneously a group of the largest sidelobes. The beam optimization was done within constraints of antenna proximity (taking into account both initial pads and reserved pad positions), antenna transporter access and no shadowing at transit for sources up to declination +15deg. When a moved pad violated these constraints it was returned to the original position. Two independent studies performed by M.Wright using MEM in MIRIAD (ALMA memos 428, 430) and S.Guilloteau using CLEAN in GILDAS,using arrays of similar design gave excellent imaging performance at all intermediate declinations.

A particularly novel aspect of ALMA is its B9 capability. The beam is quite small at that band and many sources will be relatively extended. The atmosphere can be unforgiving, compromising our ability to make use of foreshortening to provide shortest spacings. Total power capability of ALMA has yet to be proven and in any event will be most difficult at the highest frequencies. I think there should be a constraint for the ES cycle 0 (ES0) compact array to provide excellent short spacing response. I note that requirements for B9 might warrant tracks somewhat shorter than +/- 3 hr but that is not a bad goal.

I think Frederic's design has too few short spacings. It was optimized for 6 hours of observation around transit. Boone states that the largest baseline available is 145m, that the uvplane may be sampled at a rate Nyquist/1.5 and that the samples may be distributed in a gaussian of FWHM=163m. This is a truncated gaussian, so there will be sidelobes.

I think that the ES0 design should address short spacings more than the maximum spacings. Although beamshape was a constraint for the full array design, it needs to be more carefully considred in theES0 configuration design I think. This graph shows the spacings available from the pads expected to be utilizeable at ES and the spacings in the Boone design, clearly a subset of the available spacings which is skewed to longer baselines:
configs ESPh0.png

ALMA_Early_Science_MW.pdf: Mel Wright presentation on ES imaging.

Topic attachments
I Attachment Action Size Date Who Comment
1mm.d-20.1h.uvdist.pngpng 1mm.d-20.1h.uvdist.png manage 30 K 2010-12-05 - 15:00 RemyIndebetouw  
1mm.d-20.6h.uvdist.pngpng 1mm.d-20.6h.uvdist.png manage 29 K 2010-12-05 - 14:57 RemyIndebetouw  
1mm.d-80.6h.ant5.shadow.pngpng 1mm.d-80.6h.ant5.shadow.png manage 12 K 2010-12-05 - 11:06 RemyIndebetouw  
1mm.d-80.6h.shadow.pngpng 1mm.d-80.6h.shadow.png manage 19 K 2010-12-05 - 11:05 RemyIndebetouw  
1mm.d20.1h.uvdist.pngpng 1mm.d20.1h.uvdist.png manage 31 K 2010-12-05 - 15:46 RemyIndebetouw  
1mm.d20.6h.ant5.shadow.pngpng 1mm.d20.6h.ant5.shadow.png manage 11 K 2010-12-05 - 10:58 RemyIndebetouw  
1mm.d20.6h.shadow.pngpng 1mm.d20.6h.shadow.png manage 19 K 2010-12-05 - 10:56 RemyIndebetouw  
1mm.d20.6h.uvdist.pngpng 1mm.d20.6h.uvdist.png manage 30 K 2010-12-05 - 15:01 RemyIndebetouw  
1mm.m51.ES.log.pngpng 1mm.m51.ES.log.png manage 99 K 2010-12-06 - 19:37 RemyIndebetouw  
1mm.m51.ESnoisy.log.pngpng 1mm.m51.ESnoisy.log.png manage 129 K 2010-12-06 - 19:40 RemyIndebetouw  
1mm.m51.carma.log.pngpng 1mm.m51.carma.log.png manage 235 K 2010-12-06 - 20:53 RemyIndebetouw  
1mm.m51mos.log.pngpng 1mm.m51mos.log.png manage 87 K 2010-12-06 - 20:54 RemyIndebetouw  
ALMA_Early_Science_MW.pdfpdf ALMA_Early_Science_MW.pdf manage 4 MB 2010-12-07 - 15:37 RemyIndebetouw  
Compact_16.cfgcfg Compact_16.cfg manage 575 bytes 2010-12-05 - 13:33 RemyIndebetouw  
ESArray_LegalPads.jpgjpg ESArray_LegalPads.jpg manage 203 K 2010-12-05 - 14:00 RemyIndebetouw  
ES_Arrays.xlsxls ES_Arrays.xls manage 238 K 2010-12-07 - 15:40 AlWootten Spreadsheet of antennas available, baselines, etc. Ignore rows 37-52, leftovers from previous spreadsheet.
Microsoft_ExcelSnap001.pngpng Microsoft_ExcelSnap001.png manage 108 K 2010-12-05 - 11:18 RemyIndebetouw  
Microsoft_ExcelSnap002.pngpng Microsoft_ExcelSnap002.png manage 105 K 2010-12-06 - 12:38 RemyIndebetouw  
alma16ant.pdfpdf alma16ant.pdf manage 1 MB 2010-12-05 - 18:36 RemyIndebetouw  
boone.carma.sma.pngpng boone.carma.sma.png manage 42 K 2011-01-04 - 12:18 RemyIndebetouw  
carmad.d40.pngpng carmad.d40.png manage 157 K 2010-12-06 - 12:47 RemyIndebetouw  
compact.plotants.pngpng compact.plotants.png manage 69 K 2010-12-05 - 13:59 RemyIndebetouw  
compact.v2.cfgcfg compact.v2.cfg manage 1023 bytes 2011-01-14 - 09:37 AlWootten Boone configurayion v2 (Dec)
configs_ESPh0.pngpng configs_ESPh0.png manage 61 K 2010-12-07 - 15:24 RemyIndebetouw  
d-20.beams.pngpng d-20.beams.png manage 100 K 2010-12-05 - 13:14 RemyIndebetouw  
d-20.v2.v1.pngpng d-20.v2.v1.png manage 176 K 2010-12-23 - 17:53 RemyIndebetouw  
d-40.v2.v1.pngpng d-40.v2.v1.png manage 157 K 2010-12-23 - 17:55 RemyIndebetouw  
d20.beams.pdf.pngpng d20.beams.pdf.png manage 121 K 2010-12-05 - 13:20 RemyIndebetouw  
es.carma.uvdists.pngpng es.carma.uvdists.png manage 39 K 2010-12-07 - 11:25 RemyIndebetouw  
Topic revision: r15 - 2011-01-14, AlWootten
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