2.9              Science IPT 

  During November, the Science IPT delivered the ICD for the inner 172 antenna pads of the ALMA Configuration.  This was considerably altered from the design approved by the JAO on 1 October and met a Level 2 Milestone for delivery of the iner configuration.  Work commenced on design of a long baseline part of the plan compatible with this new inner portion,

 

             A Level 3 Milestone for December 2002 will produce a draft of  requirements document ready for reviews.

 

     Final testing for one of the two amplitude calibration devices being  considered for ALMA, the subreflector dual load device, commenced at BIMA. A plan for initial testing of the other device, incorporating a semi-transparent vane, was discussed at a calibration telecon, at which progress on the memo  review process (particularly that on the theory of the semitransparent vane system) and other issues was also discussed.

 

The Science IPT arranged the agenda, minutes and telecon for the ASAC on  6 November. Several Science IPT staff telecons were held, regular Science IPT leaders

telecon continued, and a further joint NA/EU Science IPT telecon was held.  Guilloteau and Wootten attended the ALMA Front-end specifications and  requirements meeting and the Back End LO design meeting in Charlottesville. Further small changes in the list of Level 3 and 4 milestones were made.

 

Anticipated activity in the next quarter

 

Milestones Level 3 and above

 

Milestone

Level

Scheduled Completion

Who?

I. B. 2. Configuration antenna motion logic

3

March 2003

MH/JC/AO

I. B. 3. Revise inner configuration

3

March 2003

JC

II. A. Calibration requirements Review

2

February 2003

BB

II. B. 1. Atmospheric modeling software available

3

January 2003

[will be late?]

JP

II. B. 2. Draft specifications for calibration devices

3

March 2003

JR/RH/JRP/JMP

II. C. 1. Bandpass calibration plan draft

3

March 2003

SG

II. C. 2. Draft of phase calibration plan

3

March 2003

??

II. C. 3. Draft of amplitude calibration plan, including Total Power

3

March 2003

??

II. C. 4. Review SSR plan for phase calibration

3

March 2003

SM

II. C. 5. Draft antenna location calibration plan

3

March 2003

JC

II. C. 6. Draft delay calibration plan

3

March 2003

SG/AB

II. C. 7. Draft antenna global pointing model plan

3

March 2003

JM

II. C. 8. Draft reference pointing/focus cal plan

3

March 2003

JM/RL/PC

II. C. 9. Draft calibration operational model

3

March 2003

SM/MH

II.D.1 Draft WVR technical aspects (with FE IPT)

3

December 2002

RH/JR

III.A.1. Draft plan on attaining ACA goals

3

March 2003

?? [K-IM]

 

There is one  Level 3 scheduled for completion in December 2002. A draft of the calibration requirements document will be produced for reviews. This is a modification of chapter 3 of the Project Book, complete with scientific examples for drivers.  The Project Scientist issued a call to the ASAC during November to provide some examples for this exercise.

 

 A Level 2 Milestone will be reached during February 2003.  This will follow the results of the Level 3 Milestone above to include completion of a review of calibration requirements with science examples complete.  This includes: phase, amplitude, bandpass, polarization, antenna  location, illumination offset, pointing, focus, delay, opacity,  and decorrelation correction.

 

Two milestones during this quarter lead to the expected June 2003 Level 2 Milestone of the review of how calibration requirements trickle down to  instrumental specifications, including special calibration devices.The first Level 3 Milestone to be achieved in  January will deliver to the project the ATM atmospheric modeling software being developed by Juan Ramon Pardo. This activity is in its final stages now.

 

A related Level 3 Milestons due in March 2003 will deliver draft specifications for calibration devices for reviews.  There will be separate specs for devices to be tested on the ATF interferometer.

 

Other Level 3 and 4 Milestones lead toward the completion of the calibration strategy for ALMA, a Level 2 Milestone scheduled for September 2003.

 

In March 2003, a draft of the bandpass calibration plan will be presented, following publication and review of an ALMA Memo describing limitations of bandpass calibration using astronomical sources scheduled for February 2003. Also in March, a draft of the phase calibration plan will be produced (Level 3). A further March milestone will be the production of the amplitude calibration plan, including total power calibration of ALMA.  A further Level 3 milestone will review the SSR plan for all phase calibration techniques,

for completion in March.  Other items scheduled for March include a draft of the antenna location determination plan, a draft of the delay calibration plan, a draft of global antenna pointing plans, reference pointing plans, focus calibration plans, and a draft of an  operational model for calibration, including ideas on sequence of moves and calibrations, dynamic scheduling, and number of antennas needed in 'calibration subarrays' .

 

Leading to the September 2004 report on WVR strategies (Level 2), a December 2002 Level 3 Milestone will present a draft document on technical aspects of the WVR, along with the Front End IPT. 

 

By March 2003, the Science IPT will prepare a draft plan on how to achieve ACA goals (flux-recovered imaging at all ALMA bands).

 

2.9.1        ASAC

 

The Science IPT facilitated the ASAC Telecons held on  6 November 2002 and 4  December 2002.  In addition, the ASAC Report to the ACC was distributed to Project and to the Public.

 

 

2.9.2    Configuration

 

New data on the terrain at Chajnantor spurred revision of the array configuration to better conform to the landforms on the site.

 

Figure 1.  The inner 172 pad positions are shown upon a greyscale indicating elevation, ranging from 4800 to 5100m.  The two yellow stars indicate the monuments ‘Master 0’ and ‘Master 71’ respectively.  The green dotted lineis the existing access road to the site from the Jama highway. The red line follows the pipeline and the red crosses note the crossing points along the pipeline.

 

The site characterization group  received the new aerial photographs and an autocad file of the site contours from the Chilean company Aerotop.  However, no digital elevation model (DEM) was included in the materials provided.  Otarola and Holdaway worked to turn the contour information into a DEM which could later be turned into a mask for pad placement in the array optimization algorithms.  Also, Angel and Holdaway studied the details of the new DEM and determined it was of far superior quality to the old one, but that the coordinates showed a systematic offset from the UTM frame.  Communications with Aerotop indicated that the coordinates were in fact not UTM and that the coordinate offset changes slightly over the image.  This resulted in a clear understanding of site topography. Large offsets (>100 m) which were coherent over 1 km scales, but which

varied over the 5 km x 5 km DEM, were found between the new and old DEM.  These offsets are attributed to errors in the old DEM.  As the extended Y+ configuration has only the old DEM to guide its antenna placement, pad misplacement (ie, onto the sides of gullys or other steep terrain) of the order of 100 m is expected to be common, and this must be sorted out in the surveying process.

 

Figure 2  The ALMA Compact Configuration.  Contours are at 0.5m intervals.

 

Holdaway worked on finalizing the Y+ configuration, adjusting the mask for terrain shadowing, inserting the new DEM mask in the center of the old Y+ mask, and removing some hard-to-access regions.  The Y+ configuration now has 42 antennas moved out from Conway's largest configuration, the highest resolution configuration is optimized

first, and the intermediate configurations are figured out after the fact by moving 4 antennas each day.  More attention is being paid to the high resolution capabilities of the array.

 

 

2.9.3    Calibration

 

Wootten, temporarily backing up Butler, on leave, organized and moderated a ALMA Calibration Group phone telecon.  Discussion focussed on the current planning for deployment of a semitransparent vane at the IRAM 30m duriing the summer of 2003 and

tests which will be made there.  Reviews of Memos were discussed;  no review has yet been received of Memo No. 423 on the theory of the semitransparent vane, so a call for reviews was urgently renewed. Wootten provided Minutes of the meeting.

 

2.9.4    Site Characterization

 

Radford and Nyman held an organizational meeting and constructed a proposed plan for construction phase activities.

 

Radford spent much of the month at the site upgrading, repairing and testing equipment--this included replacement computers for the 225 GHz tipper and the Site Testing Interferometer, installation of two new surveillance cameras, reinstallation of the seismometer, restarting the lightning detector, installing updated radiosonde software and diagnosing and repairing submillimeter tipper at Sairecabur.  Radford also observed

with the SAO team at Sairecabur.

 

2.9.5        Science Software Requirements  

 

       Myers worked on responding to comments on his work with the Science  Software Requirements group on audit requirements for aips++.  Mangum also works with this group, as do the project scientists.

 

2.9.6        Imaging

 

Holdaway has added 1/f noise to the total power atmsopheric simulations, which observe in both beam switched and on-the-fly modes.

 

Holdaway has made a preliminary study of a fast switching decorrelation correction, in which the atmospheric phases measured on the calibrator are used to estimate not only the mean phase correction to apply to the target source visibilities, but also the degree of decorrelation to correct the amplitudes by.  This work indicated that the correction worked well to correct the flux scale and recover the correct peak flux, but that it increased the image noise level.  More detailed studies will follow.

 

 

2.9.7    Organization

 

The organization and planning for the Science IPT during the construction phase of ALMA was reviewed and discussed with Science IPT members during the monthly telecon.  Weekly telecons between the three project scientists continue, and there is a monthly telecon of the NA Science Team.

 

2.9.8    Meetings, Outreach and Public Education

 

Appendix A to the ASAC Report presented October 2002 was 'Report of the ASAC Subcommittee on Site and Stringency' which included efforts of the Science IPT Site Characterization Group, including undergraduate summer student Selby Cull.

 

Science IPT Meetings during November, along with topics discussed, included:

 

Science IPT Telecon 19 November 2002 News-- Science IPT Organizational Chart, Milestones, Subgroup Reports, Upcoming Meetings

 

NA Science IPT Telecons

5 November 2002 News-- ACC Meeting, ASAC Meeting and Report, FE/BE Reviews, Milestones v3.

26 November 2002 News-- FE/BE Reviews, Total Power on ALMA, Calibration discussion

 

 

 

 

            Report for ALMA Calibration and Imaging

                         November 2002

                       NA Progress Report  

 

Overview

 

Milestones Achieved

    

 

Configuration

 

 

Calibration

 

 

Site Characterization

 

 

Science IPT ALMA Papers