ALMA/US Imaging and Calibration Group

Minutes for meeting Tuesday, 24 Apr 2001 at 4:00pm EST.

(Agenda in black, comments from notes on meeting (minutes) in blue.

Date: 24 Apr 2001

Time: 4:00 pm EDT (2:00 pm Socorro, 1:00 pm Tucson)

Phone: (804)296-7082 (CV SoundStation Premier Conference phone).

Past ImCal minutes, etc on MMA Imaging and Calibration Division Page

ALMA - Tom Leher

The loveliest girl in Vienna
Was Alma, the smartest as well.
Once you picked her up on your antenna,
You'd never be free of her spell.

Her lovers were many and varied
From the day she began her - beguine.
There were three famous ones whom she married,
And God knows how many between.

Alma, tell us,
All modern women are jealous,
Which of your magical wands
Got you euros and dollars and yens?

The rest.

--------

Agenda

--------

News -- Wootten

Any volunteers to help Crystal and Mark Claussen 'man' the ALMA booth? The lucky one gets to wear my ruby slippers.

finley, wrobel, walker, ulvestad, momjian in addition to claussen & brogan are attending the AAS from Socorro - BB

--------

ASAC The ASAC minutes are available.

--------

New Compact Configuration Designs -- Kogan

As I remember it was recomended by the committee at Grenoble to present a compact configuration at the middle of April.

I have put the version of the compact configuration at my web site.

A teleconference between Leonia and the antenna group last week was held.

Leonia has designed a new compact configuration with 30m road wide. "The configuration has 30meter road width and 200meters total size. The 30 meter width roads allow the access to any antenna without stoping of observation by any other antenna.

The previous configuration I put at my web side has 20 meter road wide and 160 meter total size. This configuration requires stop observatio at some antennas to allow the transporter to get the antenna which we want to move.

So the last configuration has the advantage in accessebility to antennas by transporter and safety and speed of antenna transportation (the road is wider).

The price of this advantage is some loosing of brigtness sensitifity.

The comparison of the beam size is given at the following table

Za,deg 0 25 30

BEAM, ",20m 1.13x1.03 1.13x1.15 1.13x1.2

BEAM, ",30m 0.95x0.82 0.95x0.91 0.95x0.93

It is seen from the table that the 'safe' configuration (W=30m) has more narrow beam by 13% (in linear measure) and 28% less brigtness sensitivity (square measure of the beam).

The question is:

__________________________________________________________________________

Does the safety/speed of antenna transportation and the accessibility cost the 28% loosing in the brightness sensitivity?

__________________________________________________________________________

There was a meeting last week among the antenna group which Leonia attended on the subject of the compact configuration. The antenna/transporter folks suggested alternate road/configuration plans to Leonia, which are apparently the configuration (http://www.cv.nrao.edu/~awootten/mmaimcal/leonia.pdf) and sketch of the road (http://www.cv.nrao.edu/~awootten/mmaimcal/leonia.jpg). The antenna group asked for a configuration with 30m roads, which Leonia has also designed. One question was posed by Leonia yesterday--does the increase in safety and speed justify the loss of brightness temperature sensitivity. Mark suggested that one way of looking at this is how much longer do we have to integrate to get the same sensitivity, and how does this compare with the time saving--60% longer or so for say 28% doesn't seem worthwhile. Mark went on to note that we really need to compare surface brightness at the same resolution. Including tapering, the surface brightness and time problems become less obviously different. Mark noted that the proper weighting of the point spread function was important. Prescription: take the primary beam, convolve it with itself, multiply that by the PSF, optimize the effective PSF you've just created. Leonia and Mark are working on these things now. I think this is rapidly converging.

To which Stephane replied: I have done some work on that too, and could give you some numbers here. One of the difficulty is the inclusion of the ACA. The ACA doesn't really match the brightness sensitivity of ALMA if the most compact configuration design is used, unless we are willing to have 20 or so antennas in ACA... The 30-m road solution would lessen the problem. Is Mark working on that too ?

AW: I'm not sure. (Mark?)

--------

New Configuration Mask - Butler

Based on the configurations PDR committee recommendations, I've created a new antenna location mask. There is a memo describing it, which should be coming out in the next little bit. You can see the memo at: postscript or pdf and I'll be making the new FITS file of the mask today, and it will sit in the same location, but be called something like 'newmask5-new.FITS.gz'.

Bryan has published the new mask (memo soon if not today), Radford is on site and Bryan will be there on the weekend. I think it is time for another configuration teleconference, to settle any remaining problems with the compact configuration and move on to the larger ones. The Chilean adventure will be over by the week of May 14, so I propose a teleconference that week. How about, say 1400UT on 18 May?

SG: Let's decide that in May 10-11...

AW: I propose to send an email to the group trying to fill in missing pieces in email traffic as above and suggesting a telecon date. Comments?

SG: Good. That would help. The decision on the "most compact" configuration is a critical one and deserves proper understanding of all the constraints.

--------

New Site DEM - Radford (already in Chile)

Last month, Angel Otarola gave me the data for a new digital elevation model (DEM) of the Chajnantor region based on the published IGM topographic maps. The new DEM covers about 51 x 51 km with either 50 m or 250 m pixels. The model'si rregular northern edge reflects missing data. The coordinates are UTM zone 19 N and E [m] on the SAm56 datum and altitudes are in m.

The new model complements two existing DEMs, a high resolution map prepared for NRAO and NRO from aerial photographs and a synthetic aperture radar (SAR) map prepared at Cornell. The high resolution map covers about 18.5 x 19.5 km with 10 m pixels. Alignment between the new DEM and this existing model is good, as should be expected since the map maker used the published IGM maps in lieu of ground control.

The SAR map covers 40 x 40 km with 20.3 m pixels. The SSE slopes of the mountains are, however, shadowed. As was previously noted, the SAR map is offset in both position and altitude from other, published maps. Comparing the new DEM to the SAR map, I determined these equivalencies:

SAR (Andes TM) UTM (SAm56)

Longitude: 2185 km W 630 km E

Latitude: 7449 km N 7450 km N

Altitude:* 5250 m 5150 m

* at Cerro Agua Amarga

The new DEM is now available in several formats

[http://www.tuc.nrao.edu/alma/site/Chajnantor/maps/igm-dem/] or

from the main map page

[http://www.tuc.nrao.edu/alma/site/Chajnantor/maps/].

Contact R. Giovanelli for the SAR map.

File names:

dem_50 or dem_250 for the 50 m or 250 m pixel model

Formats:

.asc.gz compressed ascii data: x, y, z

.fits.gz compressed fits image

.gdf.gz compressed gildas image

.ps.gz contour map, compressed postscript

.pdf contour map, acrobat 4.0

--------

Calibration Meeting -- Wootten

The deadline for the reservations for the calibration meeting is imminent.

--------

ALMA Conference Proceedings, Synergy meeting 24 May in DC

The synergies of ALMA with the GSMT Conference will be in DC on 24 May (Note slight change of date!). The one day workshop has the goals of (1) delineating potentential synergies between ALMA and a 30-m O/IR telescope (the Giant Segmented Mirror Telescope, GSMT, described in the decadal survey); (2) defining issues for more detailed studies aimed at deeper understanding/quantification of those synergies; and (3) planning a broader community-based workshop to be held in winter, 2001. The workshop will be small (fewer than 15 invitees), informal and focussed on defining next steps rather than reaching definitive conclusions. Participants will summarize from her/his perspective a key science problem for which joint GSMT and ALMA observations would significantly enhance solution. Specifically, we would like to summarize: