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ACA Calibration Plan

ACA Calibration Plan. B. Vila-Vilaro ALMA-J Project Office, NAOJ. SSR Meeting, Charlottesville, 20-21 Nov 2005. Glossary. 12m Array : ALMA-B, baseline array provided by NA/EU ACA (Full Array): (ACA) 7m Array + (ACA) TP Array

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ACA Calibration Plan

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  1. ACA Calibration Plan B. Vila-Vilaro ALMA-J Project Office, NAOJ SSR Meeting, Charlottesville, 20-21 Nov 2005

  2. Glossary • 12m Array: ALMA-B, baseline array provided by NA/EU • ACA (Full Array): (ACA) 7m Array + (ACA) TP Array • (ACA) 7m Array: 12 x 7m antennas provided by ALMA-J. Mainly used as an interferometer • (ACA) TP Array: 4 x 12m antennas provided by ALMA-J. Mainly used as single-dishes for TP (zero spacing) data. • Coordinated observations: Observations of a common program by 12m Array and ACA that are executed separately. No cross-correlations between 12m Array and ACA are taken. Main Mode • Combined Array (Mode): 12m Array + 7m Array (+ TP Array) operated as an interferometer. • Stand-alone Observations/Mode: ACA observing projects that are not included in the 12m Array schedule.

  3. The ALMA Site Pathlength error (microns) estimates due to tropospheric PWV fluctuations. Estimated extrapolating the SSF measured on site with the STI data at 300m and 11GHz. Computed at 60 degrees ELV. In red, conditions that cause 10% decorrelation at 950 GHz (2% at 345GHz) In blue, conditions that cause 10% decorrelation at 345 GHz

  4. A reminder on Sensitivities • Point-Source Sensitivity comparison ALMA 50 antennas vs. ACA 7m + ACA TP • Same Tsys and receivers, different correlators, current antenna specifications,no decorrelation

  5. ACA Design Properties • 2 types of antennas (ACA TP and ACA 7m) • Nutators on ACA TP Antennas • 2 configurations for ACA 7m Array, ACA TP Array on fixed stations • Two sub-arrays • Very compact configuration (wind crossing times ~few sec) • OPT telescopes on all antennas • WVR on (at least) the ACA TP Array • ACA correlator • Rest of Hardware similar/same as ALMA 12m Array • Coherence times > 100sec • Lower Point-source Sensitivities than ALMA 12m Array

  6. Main Calibrations • Things you want to know at the time of data collect. (ideally): a) Pointing, Focus, Feeds b) Main Reflector Shape, Beam Shape c) Station Location (Baseline) I d) Delay (electronic, atmospheric,structural,source position) I • Things that can be corrected offline: a) Amplitude b) Bandpass c) Phase (atmospheric, system) I d) Side-band Ratios e) Polarization

  7. Pointing Calibrator Requirements: ACA full, Interferometric:  350 mJy @ 90GHz (15s/point) ACA TP antennas:  510 mJy @ 90GHz (15s/point) Pointing pattern: TDB 5-point, scan, triangle, etc • All-Sky: ~2” RMS. Global positioning of antenna. Includes all structure-related terms and receiver offsets. Key in acquisition of sources separated by large angles. • Offset: ~0.6”RMS. Important for local positioning of antenna. Key role in switching to nearby calibrators. Up to 4deg separat. • Types: Continuum Spectral (TP only) • Modes: Interferometry Single-Dish OPT/NIR

  8. Tuning • Initial Pointing + Focus Loop • Main Pointing Sequence • Pointing: • Get next source from • Catalogue • b) Correct to apparent coordinates (refraction) • c) Move antenna(s) to apparent position • d) Execute Pointing Pattern • e) Solve pointing • f) Update antenna pars/Pointing File Pointing Focusing Pointing Pointing Pointing(I): All-Sky • Normal Operations: Interferometric, ALL ACA antennas, wide AZ and ELV coverage,continuum • Full Band 3 + Other Band Offsets • Frequency: ~monthly, ACA reconfiguration, etc • Duration: 1-2 hours • Other Modes: OPT, Single-dish (nutator, PSW) • Requirements: Refraction Correction,Model Fit

  9. Up to 2 bands tuned • (ref pointing band on stand-by) • At start/after some observing, switch from observing band to pointing band. • While slewing bring stand-by band up and set-up necessary relative focus positions/update pointing model • Pointing on Reference Band • Update Collimation pars of telescope • While slewing back bring back obs band and set-up adequate focus/pointing/Ref band to stand-by • Re-start normal observing • Tuning • Stand-by • Observing • RX Change • Wake-up + Other set-ups • Pointing Pointing(II): Offset • Normal Operations: Interferometric with ALL ACA antennas (spec up to 4 deg separation), single nearby calibrator (self-pointing possible),continuum • Referenced to Band 3 for high frequency bands, up to Band 4 pointing on same Band. • Frequency: ~15 mins (?) • Duration: ~1min • Requisites: Refraction correction, Band 3 stand-by, Focus Relative Offsets/Relative Pointing Models

  10. Tune RX to desired Band • Bandpass Calibration • Go to brightest countinuum point-source at desired ELV (can be same as BP) • Point loop • Raster Map keeping one of the antennas fixed while scanning others. Switch antennas at some point. • Output Data to disk for offline processing Tuning BP Calib Point+Foc Loop Raster Map Phase-retrieval & Interferometric Holography modes Optics Raster Maps/OTF • Main Dish Surface, Holography: OSF @ 90GHz AOS (TBD) 2 hour map, <1sec/pixel, 128x128 TP ant 68x68 7m ant 90GHz, 10m RMS  20-40Jy sources • Beam/Illumination Pattern Measurements (Including Polarization): ELV dependency, ALL bands • Feed alignment procedures: Only required when installing RX back on telescope • Focus (3 axes): TP Antennas, Focus curves 7m Antennas + TP, Interf Focus Frequency: As Needed (once per tuning+tracking?)

  11. Tune RX • Pointing/Focus Loop • Execute Loop of short synthesis observations of a Gain calibrator and several baseline calibrator sources • Loop involves going to next source in catalogue (apparent coordinates) and performing a ~30sec synthesis • Data output to disk for offline processing Tuning Pointing Focusing Pointing Gain Calibrator Calibrator Calibrator Baseline • Specification: 33m per antenna location (Takakuwa 2005) • Normal Operations: Continuum Interferometry with ALL ACA antennas • Band 3, objects distributed to cover wide range in Hour Angle and DEC. • All-sky pointing model is enough. Instrumental phase corrected periodically by observations of single calibrator. • Frequency: Once per array re-configuration, antenna addition, special situations • Duration: ~2hr/session • Requirements: As for pointing, good weather

  12. Electronic Delay Measurement • Tune each RX, both polarizations • Go to bright continuum point source • Short synthesis on source • Setting Band 3 as receiver delay reference one gets the IF terms • For other Bands, get Receiver delays from measured IF delays • Fit of phase slope done offline • Self-pointing/Focus optional (Default values possible) Tuning Delay 1 Delay 2 Delay • Source Positions: 1/10 of Max Freq. Synthesized Beam  0.1”, 12m Array 0.7mas • Atmospheric (bulk): Must be calculated per antenna (~130fs at low elevations for the ACA) • Structural: Metrology • Electronic (chromatic): bright compact continuum source. Needs to be done for all bands and polarizations. Should be fairly stable with time once measured. ALL ACA antennas

  13. Tuning • Tune to observing frequency • Initial Set-up Observations (pointing+focus loop) • Go to Target source • Start Observing loop that includes amplitude calibration and observations. • Amplitude calibration is in three steps (TP observation mode): • a) Input Load 1, Set ATTNs (if needed), Integrate 1-2sec, Release Load 1, reset ATTNs (if needed) • b) Input Load 2, Set ATTNs (if needed), Integrate 1-2sec, Release Load 2, reset ATTNs (if needed) • c) Move antenna OFF target source, Observe SKY and return to source • Data output from the three observations is used to calculate Tcal. Tau calculated/measured too. LD1 Relative Amplitude Cal LD2 Calibration TAU SKY Observ • For Jy/K synthesis observations of known calibrator are used Amplitude • Relative: Allows comparison of data within observing band and data merging between arrays. Repeatability of observations. • Absolute: Accurate physical quantities. Accurate line ratios. • Relative • 3% for up to Band 7, 5% above • Method: Dual-Load + Tau Measurement in TP mode • Requires: Atmospheric model, antenna parameters, SBR (TP),f • Frequency: a few mins • Absolute • 5% for all bands • Method: Standard Calibrator obs. • Requires: Boostrapping, good primary calibrators • Frequency: Once per dataset

  14. Tune to obs frequency • Set-up for Spectral Mode • Pointing/Focus Loop (on Self) • Synthesis Observations of Calibrator (~1hr) • Save data to disk for offline reduction • Proceed with other observations Tuning Spectral Mode Set-up Pointing Focus Pointing Synthesis Observ Bandpass • Use of combined modes: (10000:1 spec) • Rest of cases: (>1000:1) • Frequency: Once per tuning • Calibrators: Bright flat-spectrum cont. sources (compact) • Method: Traditional  high decorrelation at high freqs. Self-Cal/Phase cal  better • ALL ACA antennas involved! Required for spectral observations ONLY

  15. Phase • Short-Term: scales of a few sec, mostly due to random structural/environment terms and atmospheric PWV fluctuations. Affect more the sensitivity of the observations (decorrelation) • Long-Term: scales of minutes, mostly due to instrumental fluctuations and long term weather patterns Affect the quality of the imaging performance

  16.                WVR • TP Antennas MUST point in the general area of the ACA 7m • During Synthesis with the ACA 7m, the WVR are taking data at 1Hz continuously • Data from WVR must be labelled with a timestamp and the WVR of origin • Calibration is done POST-CORRELATION O B S E R V Phase(I): Short Term • WVR on the ACA TP antennas: 10(1.25+w)m • Decorrelation: Measuring 1sec average EPL along line of sight at 4 corners of array. Direct decorrelation for ACA TP, and extrapolated for inner ACA 7m. • Phase Variations: Relative to last long term value. Extrapolated to inner ACA 7m Array. Asaki(2005), ALMA Memo 535

  17. Tune up to 2 Bands. Reference Band on Stand-By mode until needed • Do some observations on Target band (pointing, synthesis, cals, etc) • While moving to calibrator bring stand-by band up and set additional parameters (pointing model, focus, etc.) • Synthesis on Calibrator (~a few secs) • Go back to target, put Reference band on stand-by and bring up Target Band with necessary parameters • Synthesis on Target • Cycles will be >100sec for the ACA Tuning Obs Stby Band Switch Phase(II): Long Term • Method: Low Frequencies  Phase Referencing to nearby calibrator High Frequencies  Phase extrapolation from Band 3 • Frequency:100sec (coherence time Band 10) Phase Transfer Schemes “Don’t Rock The Boat” “Controlled Roll-Over” Don’t move the subref much Track movement of subref Advantages: Advantages: You “know” where the tel. structure isYou “correct” for the tel. structure Difficulties:Difficulties: Loss of Sensitivity Subref tracking must be accurate Differential Pointing Model RequiredLonger Switching Time

  18. Side-Band Ratio • Important issue in DSB receivers and TP observations. Interf. quite time consuming. • Frequency: once per tuning • Calibrators: a) SSB standards/Referencing b) Artificial Line Injection c) two ELV method (ALMA Memo 505) d) Skydip + ATM modelling

  19. Polarization • Linear vs. Circular Reception: -Circular reception is easier to calibrate -BOTH TP and 7m Array should observe same type -TP is quite more challenging than Interf (Tsys term) -Effects of off-axis polarization on mosaicing need to be studied -Scaling of TP to Interf would be advisable • Calibrators: currently no good calibrators available for the high frequency ALMA Bands. Will require surveys.(Planets???) • Role of artificial signal injection is currently being studied

  20. ACA Calibration Issues • Refine Calibration Specs & Reqs • Detailed Calibration Use Cases • Optimization of Cal Techniques • Operation Cycles/Scheduling Impact • Imaging/TP Simulations • Combined Array Issues/Data Merging • Array Design Completion • Polarization • Hardware Issues (Nutators, WVRs, P-Cal)

  21. ACA Operation Concept

  22. Unification with baseline array under JAO JAO AIV Phase CSV ALMA AIV Phase CSV Unified Operation Partners

  23. Impact of ACA • Department of Science Operations: 1) Array Operations: not major 2) Program and Data Management: not major • Department of Technical Services: 1) Antenna Group: 20-25% increase, 3-5 turno personnel 2) Electronics Support for FE: 20-25% increase, 3 turno personnel 3) Electronics Support for BE: 1 turno personnel 4) Computing Group: not major 5) Maintenance Group: not major 6) System Enginneering Office: not major 7) Spectrum Management Office: not major 8) Technical Information System Office: not major • Others: Antenna Transporters, FE Service Vehicles (cost study), Maintenance Impact

  24. ACA Scientific Operation Timeline (TBD) 2009 Dec Early Science Obs with TP Array (1) 2010 Q4 Early Science Obs with 7m Array (6) 2012 Q1 Full Science Obs with ACA • Unification: IPRC  LTQ • ACA User Interface: As close as possible to that of 12m Array • Ops Scheme: a) Coordinated Obs (main) b) Combined Mode (BLC) c) Stand-Alone (minor) • ACA 7m re-configurations: inner 6 ant fixed 60:40 sky coverage ~bimonthly (TBD) • ACA Stand-alone: -TOO -Beam-size Matching Obs (hybrid?) -Absolute Flux Scale Maintenance • ACA availability: 95%

  25. Operation Modes • Long-Term: -Short time lags: Symmetric -Long time lags: ACA trailing • Short-Term: 7m and TP used during calib independent modes afterwards • Combined Mode: -Projects that require high calibration precision -Significant Increase in Sensitivity (Iono) • Stand-Alone Mode: Same as coordinated obs higher spectral resolution modes (TBD) Usually 7m + TP Array

  26. ACA Data Rates • 12m Array data rate to ALMA archive is ~6MB/s (average) and ~60MB/s (sustained) • Simple scaling by baseline numbers implies: ~0.36 MB/s (average) & 3.6 MB/s (sustained) • Combined Mode: 50 + 16 (init)  x 1.06

  27. Schedule Flow • ALMA arrays • 12m Array ONLY • TP Array ONLY (minor) • ACA ONLY (standalone mode) • 12 Array + ACA TP Array (coordinated) • 12m Array + ACA Full Array (coordinated) • 12m Array + ACA @ different frequencies • Combined Array • Combination of modes • ACA Necessity Checker • ACA Sensitivity Calculator Call For Proposals ACA? Proposals + ? • ACA Priority • Completion Policy • ACA Dynamic Scheduler (7m & TP), BALMA for Combined Mode(?) ACA PL ALMAB PL Review Scheduling 7m Array Re-Configurations -Normal: 12 weeks (TBD) -NS Extension: 8 weeks (TBD) + Execution Observations • Data Delivery • Data Proprietary period Data Data Pipeline

  28. Summary of Science Deliverables • ACA raw uv and visibility data for targets and calibrators (quality-assured) • ACA processed images and combined images • Off-line reduction software for data combination • Proposal preparation software tools (ACA) • ALMA users manual with ACA sections

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