FP6 Workpackage 5: Advanced Radiometric Phase Correction (ARPC) JAO – ALMA Enhancement Team Meeting Bojan Nikolic (Project Scientist for Advanced WVR Techniques) John Richer (Project Leader for Advanced WVR Techniques) Cambridge 24 July 2009 Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 1)
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10–15 s (fast antennas!)I Expect calibrators about two
degrees from science targetI Can calibrate at 90 GHz and
transfer up to 950 GHz
+
Water Vapour RadiometryI Measure atmospheric
properties along the line ofsight of each telescope
I Use dedicated 183 GHzradiometers on eachtelescope
I Measurements at about 1 HzI Infer excess pathI Correct either in correlator or
in post-processing
+ Self-Calibration in a limited number of cases
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 5)
Fast switching phase calibration(Simulation)
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Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 6)
The 183 GHz Water Vapour LineBlue rectangles are the production WVR filters
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T b(K
)T b
(K)
175 177.5 180 182.5 185 187.5 190
ν (GHz)ν (GHz)
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 7)
Goal for ALMA Phase Calibration
I Formally:
δLcorrected ≤(
1 +w
1 mm
)10µm + 0.02× δLraw (1)
I For most projects the above means atmospheric fluctuations areeliminated as a scheduling constraint
I ALMA will rely on accurate phase correction→ If it doesn’t work as expected for a project, the scientificobjectives are likely to be compromised
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 8)
WP5 Description from Contract
Description of workDevelop more sophisticated atmospheric models both ab initio butalso through the empirical analysis of the radiometric data alreadytaken at the Sub-Millimeter Array (Hawaii) and later from the ALMAsite in Chile, from Early Science onwards. Implement and test thesemethods as part of the ALMA software system, with the deliverablebeing a turnkey system in the ALMA pipeline by the end of the project.
Deliverable D9Complete software package for correcting phase and amplitudeerrors applied to the ALMA astronomical data integrated into theALMA system. The software will be released in stages in accordancewith the standard ALMA Computing release cycle, with increasingfunctionality in each 6-monthly release.
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 9)
WP5 within the ALMA Project
Radiometric phase correction is a part of baseline ALMA.
It was however recognised thatI phase correction by water vapour radiometry is a complex
technique that needs an extended research and developmentprocess to become a simple and usable solution for astronomersand the observatory;
I ALMA had limited resources in the Science and Computing IPTbudgets for this work;
I Leadership and expertise in this within European institutionsmade it attractive to continue the technical development in here.
WP5 grew out of this: we recognised that we could significantlyenhance ALMA’s scientific capabilities using European expertise.Enhancement comes in two forms: better phase correction (hencebetter imaging and sensitivity) for a given observation; andcapabilities to exploit wider range of weather conditions (efficiency).
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 10)
Summary of current status of WP5
I All internal milestones as agreed at the start of the project havebeen achieved so far (and associated payments made by ESO toUC)
I Project is fully staffed (Richer/Nikolic/Curtis)I 4 ALMA memos covering aspects of WVR phase correctionI First field trip to the site commencing tonight!
I Tests at the OSFI Discussion/collaboration with ALMA staff
I We have requested a zero-cost extension to the work package toallow it to overlap with Early Science – end date Dec 2011
I No realistic test data yet – all work so far either theoretical or withshort sections of SMA data
I ‘Baseline’ radiometric phase correction only now being designedand implemented
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 11)
Internal MilestonesAssuming Dec 2011 completion
1 Oct 2007 Report on the testing at SMA. Report on effect of beam-mismatch.
1 Apr 2008 Initial version of on-line stub code. Reports on implications ofobserving strategies and antenna vs baseline correction.
1 Oct 2008 Initial version of physics-based algorithms and report on this.1 Apr 2009 Refined version of physics algorithm. Initial version of
machine-learning based algorithm1 March 2010 Report on initial testing at the AOS. Refinement of physics
algorithms. Measurement of empirical correlation phase andWVR output.
1 Dec 2010 Machine-learning algorithms based on real data. Report onthis approach.
1 June 2011 Near-final algorithms based on extensive AOS testing31 Dec 2011 Final revised versions of algorithms and documentation, and
report on their performance after Early Science feedback
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 12)
Primary outputs of WP5 so far I
I Full analysis of test data from the SMAI Written up as a note distributed to the project
Date Time Elev Baseline Raw σφ 5-minσφ Res. c Spec Sampling Comment(UT) (deg) (m) (µm) (µm) (µm) (mm) (µm) (s)
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 13)
Primary outputs of WP5 so far II
I Simulation of errors due to partial overlap of WVR andastronomical beams
I Documented as ALMA Memo # 573I Implemented in C++/Python and publicly available under LPGL
Turbulent layer at 250 m Turbulent layer at 750 m
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δθ (arcmin)δθ (arcmin)
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 14)
Primary outputs of WP5 so far III
I Simulation of ALMA phase correction strategy as a systemI Documented as ALMA Memo # 582I Implemented in C++/Python, publicly available under LPGL, and
compatible with CASA
Positional error Fractional flux error
0.001
0.01
0.1
1
√ 〈∆P
2〉(
arcs
ecs)
√ 〈∆P
2〉(
arcs
ecs)
0.01 0.02 0.05 0.1 0.2 0.5 1 2 5
φrms (rad)φrms (rad)
0.001
0.01
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1
√ 〈S2〉−
〈S〉2
/〈S
〉√ 〈S
2〉−
〈S〉2
/〈S
〉0.01 0.02 0.05 0.1 0.2 0.5 1 2 5
φrms (rad)φrms (rad)
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 15)
Primary outputs of WP5 so far IV
I Calculation of phase correction coefficients from ab-initio andempirical methods
I Documented in detail as ALMA memos #587 and #588I Fully implemented in standalone C++ and made publicly available
under LPGLEstimated Optimum
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m)
p(µ
m)
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m)
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m)
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m)
∆p(µ
m)
Residual RMS 74µm Residual RMS 71µmNikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 16)
Primary outputs of WP5 so far V
I Technical input for reviews of the production WVR hardwaredesign
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 17)
Highlight of recent progress
I Basic versions of both ab-initio and empirical algorithmsimplemented and shown to produce encouraging results with theSMA test data
I Emily Curtis joined us in April (working part-time on phasecorrection) and she’s now up to speed on the project
I First data from the OSF with production WVRs this monthI Mid-term review successfully passed
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 18)
Near-term plans
I Trip to OSF/AOS to collect WVR sky brightness data, talk toALMA staff, and familiarise with the operation of the telescopes(next two weeks)
I Analysis of sensitivity of the dispersive scaling factor toatmospheric conditions (e.g., ground level temperature, watervapour scale height)(some results already available)
I Analysis of the WVR sky brightness data from OSF/AOS(next three months)
I Initial design of the CASA interface(probably commence in September)
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 19)
Test Data
Realistic test data is a critical input to our work, in order toI Understand in which directions to further develop the algorithms
we already haveI Test how well the algorithms work and tune them from use in
productionCurrently we have:
I About five hours of useful test data from the SMA with theprototype WVRs
I Sky-brightness data from production WVRs in the lab at OSF(collected in the beginning of July)
Near term test plan exists and we fully support it:I Distributed by Richard HillsI 18 items of which about 5 completed already
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 20)
Test Data Shopping list
Ideally we would have simultaneous interferometric and WVR skybrightness data:
I With good instrumental phase stabilityI Taken at the AOS (but at OSF would be useful too)I Over a range of atmospheric conditions (daytime/nighttime and
winter/summer)I In a number of different configurations (compact to most
extended, where the challenge is greatest)I Over a range of observing frequencies (to understand dispersive
effects)Extension of work to December 2011 is crucial to getting the majorityof these data
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 21)
Integration plans
I It will be possible to do phase correction both on-line (based inthe TELCAL package) and off-line (CASA)
I All code already developed is standard C++/Python andcompatible with both systems
I The plan is to first integrate into CASAI Offline correction is better except in cases where limited by high
data ratesI Initial testing of algorithms will always be done off-lineI This integration is straightforward and can largely be done
independently of main CASA developmentI One proven, some algorithms will be integrated into TELCAL
I Only a subset of algorithms will be suitable for use in TELCALI Code already produced can be called from TELCALI Integration will be more straightforward once baseline algorithms
are implemented
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 22)
Risks/issues to keep in mind
I Availability of suitable quality/quantity test dataI Much reduced with the extension to Dec 2011
I Loss of key personnelI Will phase transfer from 90GHz work well enough? If not
alternative strategies will need to be developedI User experience of (offline) phase correction
I Integration into pipeline processing?I Added complexity to off-line data reduction?
I Role of WVRs in absolute flux calibration?I Input from phase correction algorithms into scheduling software
I How well can we predict residual phase fluctuation?I How do we decide on fast-switching cycle time?
Nikolic & Richer, U. Cambridge JAO – ALMA Enhancement Meeting: WP5 ESO 24 July 2009 (slide 23)