ACA Calibration Plan

B. Vila-VilaroALMA-J Project Office, NAOJ

SSR Meeting, Charlottesville, 20-21 Nov 2005

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.

Glossary

The ALMA Site10m 20m 30m 40m 50m

10 7.2 10.7 13.6 16.1 18.3

20 10.2 15.4 19.6 23.3 26.6

30 13.6 20.7 26.5 31.6 36.1

40 17.9 27.4 35.1 41.9 48.0

50 23.7 36.4 46.7 55.7 64.0

60 31.7 48.7 62.5 74.6 85.6

70 43.7 66.7 85.3 101.6 117.0

80 63.6 95.4 120.9 143.0 162.9

90 108.6 154.2 190.6 221.3 248.2

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

A reminder on Sensitivities

Point-Source Sensitivity comparison ALMA 50 antennas vs. ACA 7m + ACA TP Same Tsys and receivers, different correlators, curr

ent antenna specifications,no decorrelation

5

6

7

8

0 200 400 600 800 1000

Freq(GHz)

Sens

itivi

ty R

atio

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 st

ations 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

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

Pointing All-Sky: ~2” RMS. Global positioning of antenna. Includes all str

ucture-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

ACA 7m

ACA TP ACA full

Interf (X) (X) X

OPT X X (X)

Single-Dish

(X) X

Calibrator Requirements: ACA full, Interferometric: 350 mJy @ 90GHz (15s/point) ACA TP antennas: 510 mJy @ 90GHz (15s/point)

Pointing pattern: TDB5-point, scan, triangle, etc

Pointing(I): All-Sky Normal Operations: Interferometric, ALL ACA ant

ennas, 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

Pointing

Focusing

Pointing

Pointing

• Tuning

• Initial Pointing + Focus Loop

• Main Pointing Sequence

Pointing:

a) 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(II): Offset Normal Operations: Interferometric with ALL ACA ante

nnas (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, Fo

cus Relative Offsets/Relative Pointing Models

•Tuning

•Observing

•RX Change

•Stand-by

•Wake-up + Other set-ups

•Pointing

•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

Optics Main Dish Surface, Holography: OSF @ 90GHz AOS (TBD) 2 hour map, <1sec/pixel, 128x128 TP ant 68x68 7m ant 90GHz, 10m 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?)

Raster Maps/OTF

Phase-retrieval & Interferometric Holography modes

Tuning

BP Calib

Point+Foc Loop

Raster Map

•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

Baseline Specification: 33m per antenna location (Takakuwa 2005) Normal Operations: Continuum Interferometry with ALL ACA ant

ennas Band 3, objects distributed to cover wide range in Hour Angle a

nd DEC. All-sky pointing model is enough. Instrumental phase corrected

periodically by observations of single calibrator. Frequency: Once per array re-configuration, antenna addition, s

pecial situations Duration: ~2hr/session Requirements: As for pointing, good weather

Tuning

Pointing

Pointing

Focusing

Gain Calibrator

Calibrator

Calibrator

•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

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

Electronic Delay Measurement

Tuning

Delay 2

Delay 1

•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)

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

Relative Amplitude CalTuning

LD1

LD2

SKY

Observ

Calibration

•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.

TAU

•For Jy/K synthesis observations of known calibrator are used

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 obse

rvations ONLY

Tuning

Spectral Mode Set-up

Pointing

Pointing

Focus

Synthesis

Observ

•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

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

Phase(I): Short Term

WVR on the ACA TP antennas: 10(1.25+w)m Decorrelation: Measuring 1sec average EPL alo

ng 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

O

B

S

E

R

V

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

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 is You “correct” for the tel. structure

Difficulties: Difficulties:

Loss of Sensitivity Subref tracking must be accurate

Differential Pointing Model Required Longer Switching Time

•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

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

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 studie

d -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

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)

ACA Operation Concept

Unification with baseline array under JAO

AIV Phase CSV

AIV Phase CSV

ALMA

Partners

Unified

Operation

JAO

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), Maintenanc

e Impact

ACA Scientific Operation 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%

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

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

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

Schedule Flow

Proposals

Scheduling

Execution

Data

Call

For

Proposals

ACA?

•ACA Necessity Checker

•ACA Sensitivity Calculator

Review+

?

ACA PL

ALMAB PL

Observations

•ACA Priority

•Completion Policy

•ACA Dynamic Scheduler (7m & TP), BALMA for Combined Mode(?)

+

Data Pipeline•Data Delivery

•Data Proprietary period

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

7m Array Re-Configurations

-Normal: 12 weeks (TBD)

-NS Extension: 8 weeks (TBD)

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