December 2001 - January 2002
Progress Report - Overview
Milestone Achieved - Configuration Design
Review Socorro, N. M. 24-25 January 2002
During December and January the ALMA Configuration
entered its final phase, beginning with the campaign at Chajnantor and
culminating in the Configuration Design Review held in Socorro. From several
possible designs for the array, one incorporating a semi-compact central
configuration designed by Leonia Kogan, mated to a scale-free spiral design
designed by Conway, was selected for further improvement. The Review Committee
drafted its recommendations, to be submitted to project management in February.
Several studies on ALMA calibration by Holdaway
were published in the ALMA Memo Series. These included an investigation
of the tapered illumination misalignments on the primary dish and how to
correct them (Memo 402), "Fast Switching Phase Correction Revisited for
64 12 m Antennas" (ALMA Memo 403) and "Atmospheric Dispersion and Fast
Switching Phase Calibration" (ALMA Memo 404).
The group also worked on the new version of the
project book. Holdaway, Wootten and Guilloteau took advantage of their
face-to-face meeting in Socorro to plan revisions to the calibration chapters.
Conway will revise the configuration chapter in concert with a revision
of the web material by Butler. Holdaway will revise Chapter 13, Data Analysis
and Imaging Requirements.
Plans were laid for discussions on Calibration
of ALMA, and on The ALMA Configuration during ALMA Week in April.
Among the Education and Public Outreach activities of the Science group were one major publication and several public lectures. The Proceedings of the conference 'Science with the Atacama Large Millimeter Array' held at Carnegie Institution of Washington during October 1999 was published.
Wootten gave the ALMA talk at the Hale Observatories,
and a version of it at the Caltech Submillimeter Observatory colloquium.
He also gave a science colloquium in Green Bank. Mangum and Radford attended
the URSI meeting in Boulder, where Mangum chaired a session on "New Millimeter
and Submillimeter Arrays" for Commission J (Radio Astronomy). Mangum also
gave a general astronomy (with emphasis on radio astronomy) lecture to
an enthusiastic crowd of about 60 retirees with lots of good questions
at the Sun City Astronomy Club.
Wootten worked on an ALMA article for a book on "Sensing Science and Technology at Terahertz Frequency". He planned an ALMA poster for the "Second Workshop on New Concepts for Far-IR Submillimeter Space Astronomy" at The University of Maryland March 7-8, 2002 and at the STScI
Symposium on "Astrophysics of Life" May 6-9 2002.
Mangum produced a poster on ALMA and stellar debris disks for the April
11-13 symposium "Debris Disks and the Formation of Planets: a Symposium
in Memory of Fred Gillett".
ALMA Software and Simulations
During the group's face-to-face meeting in Socorro, Guilloteau installed the IRAM GILDAS simulation software on Wootten's laptop and gave a brief demonstration. This powerful software allows the rapid evaluation of the imaging capabilities of ALMA. Myers produced the ALMA Offline Data Processing
Requirements document for the software group
and received ImCal and referees comments.
Holdaway has been setting up simulations for
a multi-scale clean imaging paper he is writing. Multi-scale clean is a
most promising deconvolution condidate for mosaicing algorithms.
Configuration
Site Characterization
Radford planned and executed the December Chajnantor site campaign. Participants included B. Butler, P. Gray, S. Radford, and R. Sramek (NRAO), G. Delgado, J. Eschway, D. Hofstadt, A. Otarola, and R. Rivera (ESO), J. Conway and L.-A. Nyman (OSO), S. Sakamoto (NAOJ), S. Yamamoto (U. Tokyo), M. Diaz and S. Paine (SAO), and R. Villanueva (road engineer). Butler had been getting the
hygrometer ready for deployment at the site during this campaign. The campaign executed a preliminary survey of configuration designs; deployed a frost point hygrometer; redeployed a second submillimeter tipper to Sairecabur (5525 m); redeployed upgraded radiosonde equipment and launched both old (AIR 5A) and new (Vaisala RS-80) sondes; reorganized the instruments in the ESO container; experimented with supplemental oxygen therapy; and performed other minor equipment repairs and
improvements. The crew also undertook various
ASTE and APEX activities, including soil resistivity tests. Radford continues
to deal with communication on the Inmarsat ISDN link.
Radford received the newest map from McLain Aerial,
covering the region south of the previous map to Toconao and reformatted
it for distribution. He also processed site data through 8 January and
updated web pages accordingly, including the radiosonde summary web page.
The tipper failed 19 December. Angel Otarola arrived in Tucson to work
on integration of the weather instrumentation system with the monitor and
control system.
Configuration
Several telecons readied new material for the
Configuration Design Review. Butler summarized all new material into a
document included with the agenda, which he also prepared as the local
organizer of the Review.
At the Review, the report of the Preliminary
Review held February 2001 was confronted with work presented by Kogan,
Conway, Webster and Boone. Although the design of configurations for radio
telescope arrays is a mature field, a number of new ideas were introduced
during the course of ALMA design: the elegant design theory developed by
Boone, the sidelobe optimization techniques presented by Kogan, the Delaunay
uv optimization introduced by Webster, and the hybrid uv then beam optimization
employed by Conway. However, the scaling and snapshot performance in extended
configurations of the Boone array were felt to compromise its suitability
without modification. The committee preferred the zoom spiral design presented
by Conway, mated to a compact design developed by Kogan, and recommended
several improvements for these designs. It further recommended that Conway
lead the effort to finish the design effort. This begins with the compact
design, with a report due during ALMA Week, and then the more extended
arrays, including consultation with road engineers, with a report due at
the occasion of the Site Development Review in the early Fall. Wootten
wrote the report of the Configuration Design Review and transmitted it
to Review Committee members for review.
Holdaway began work on a multi-resolution array
optimization algorithm. This algorithm could be applied to the compact
configuration to optimize the sidelobes in a new way. At the CDR Otarola
had noted that the access road to the site from the OSF might be used for
a larger Y-shaped array, taking advantage of existing roads and eliminating
the necklace around Chascon which had characterized earllier work. Holdaway
and Otarola began an investigation which appears to be very promising.
Holdaway also performed some simple analysis of the various compact configurations'
properties with respect to source declination and hour angle.
Calibration
A calibration meeting was planned for ALMA week,
including what site characterization group can do, water vapor monitoring,
IRMA (deployment perhaps in May), and ATF testing plans (semi-transparent
vane, hot loads in the subreflector and the photonic phase calibration
system).
Holdaway reported on his investigation of the
effect of tapered illumination misalignments on the primary dish. Detailed
numerical imaging simulations indicate that after simply correcting the
(u,v) coordinates to offset the misalignment, the image quality is restored
to the level expected when illumination offsets are not present. This work
is published as ALMA Memo 402.
Holdaway studied fast switching phase calibration using a more complete optimization with fewer assumptions, updated sensitivity, antenna slewing, and atmospheric information. He concluded that the slew profiles provided by Vertex are sufficient. The residual phase errors resulting from fast switching will cause baseline-dependent decorrelation. Some minor algorithmic work should proceed on fixing this decorrelation. It seems likely that the phase information gleaned from observing the calibrator will be sufficient to accurately estimate the decorrelation correction on a per baseline basis
(ALMA Memo 403). Dispersive phase problems in
the submillimeter wavelength windows may very well complicate or even limit
the fast switching calibration (ALMA Memo 404). During the 10th percentile
atmospheric stability conditions, on baselines of 1000 m, the fast switching
residual phase will be dominated by the uncompensated dispersive phase
at the edges of the sub-millimeter windows (ie, at frequencies where the
transmission is less than 50% of the peak transmission for that window).
This will markedly affect the ability of fast switching to correct atmospheric
phase errors for sub-millimeter observations. Longer baselines could be
accommodated by observing during better conditions or by observing near
the window center where the dispersive phase is close to zero. If dry phase
fluctuations are smaller than the dispersive phase, as will almost certainly
occur far from the window centers, the dry phase can be ignored and a correct
accounting for the dispersive phase from a transmission model such as ATM
can be applied.
Holdaway also began work on overhauling the Imaging
and Calibration chapters of the project book.
Mangum worked on pointing of the ALMA antennas. He started into the task of developing the subroutine which will calculate refraction for the prototype antenna control system. Wootten and Mangum visited the Owens Valley Radio Observatory to observe and to review the status of the Water Line Monitoring (WLM) system there. The WLM is best used for long baselines at high frequencies; the array was in its longest baselines but the weather was pretty poor. They had discussions with John Carpenter regarding software interface to phase correction system. OVRO has developed a very nice IDL-based interface to their hardware. The system is not, however, in general use yet at OVRO.
They also became reacquainted with the java-based
monitor and control system used at OVRO. This is a very nice interface
which naturally allows for remote observing (one only needs a browser to
run it). Much of the look-and-feel is similar to the 12m monitor and control
system, which was widely heralded as a well-designed system.
Science IPT ALMA Memos
405 Unaddressed Issues for ALMA Configurations M.A. Holdaway (NRAO) 01/02
404 Atmospheric Dispersion and Fast Switching Phase Calibration M.A. Holdaway (NRAO/Tucson) and J. R. Pardo (Inst. Estructura de la Materia Dpto. Fsica Molecular Serrano) 12/01
403 Fast Switching Phase Correction Revisited for 64 12 m Antennas M. A Holdaway (NRAO/Tucson)
12/01
402 Illumination Taper Misalignment and Its Calibration M.A. Holdaway (NRAO/Tucson) 12/01
400 A Proposal of Optimized Configurations for the ALMA Frederic Boone (Observatoire de Paris) 01/02
Meetings Held
ALMA/NA Imaging and Calibration meetings and list of topics discussed
* Telecon on 18 December 2001: Report of Visit to Chajnantor, Bore Holes, Configuration Design and Review
* Telecon on 15 January 2002 Configuration: CDR Agenda
* Configuration Design Review Socorro, N. M. 24-25 January 2002
ALMA Science Advisory Committee Meetings and list of topics discussed
* Telecon on 5 December 2001: AEC Meeting Report, US Funding Status, Configuration Crew on Chajnantor
* Telecon on 16 January 2002: AEC Project Definition, Antenna Progress, Configuration Design Review, Chile Status, Regional Science Centers, aips++ Tests
ALMA Co-ordinating Committee Meetings
* Telecon on 11 December 2001 Attended by Wootten