The ALMA TelCal subsystem

Dominique Broguière , Institut de RadioAstronomie Millimétrique (IRAM)

Casa Developers meeting - 12/05/2010

12/05/10

TELCAL subsystem 2

Introduction• TELCAL is the on-line calibration software for the ALMA array

– 50+16 mm/submm antennas on Chajnantor Plateau (5000m) in Northern Chile– financed by Europe, Japan, Northern America.

• People involved in TELCAL :– Robert Lucas (lead), Dominique Broguiere, Jean-Christophe Roche, Juan Pardo (ATM)– Former members : Fanny Cosson, Takeshi Nakazato

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TELCAL subsystem 3

TelCal Requirements

2 important requirements in the SSR (Science Software Requirements) document :

• The TelCal subsystem must use ACS (Alma Comm on Software) services to retrieve data, publish data, log errors.

• The TelCal subsystem must return results typically 0.5 second after having received the data, for some time-critical operations, like pointing, focusing, …

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TELCAL subsystem 4

Data processing

• Calibration results sent to other subsystems (not applied by TELCAL on the raw data)

• TelCal process only calibration scans (scan intent = pointing, focus, delay, atmospheric calibration…)

• Observed sources : calibrators

• Data origin : – in singledish mode : totalpower data or autocorrelation data– in interferometric mode : crosscorrelation data

• Input dataset : ASDM • Output result : ASDM containing calDM tables

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TELCAL subsystem 5

Calibration engines

Frequency based calibration : the results are used by Telcal to combine data from several basebands• Bandpass => frequency based polynomial (phase and amplitude)• Sideband gain ratio => gain ratio

Calibration engines : pieces of software associated to each type of calibration. According to the calibration intent, the Telcal engines can be classified in 4 categories :

• Instrumental adjustments : the results are used to apply some corrections to the instrument• Pointing => pointing offsets in X and Y (singledish or interferometry)• Focus => focus offset in X or Y or Z (single dish or interferometry)• Delay => delay offset (interferometry)• Antenna position => antenna position offsets (x,y,z) (interferometry)• Pointing Model => pointing model coefficients (singledish or interferometry)• Holography => panels adjustment to improve the surface RMS

• Monitoring of the system on astronomical sources : the results are used to monitor the quality of observations

• PhaseCal => phase rms on each baseline• AmpliCal => efficiency (K/Jy) • PhaseCurve => time based polynomial fit of the phases• AmpliCurve => time based polynomial fit of the amplitudes

• Atmospheric calibration : the results are used to correct the data from the atmospheric variation effects. Based on ATM library

• TemperatureScale (power measured on 2 loads + sky) => tsys, water • Skydip => forward efficiency and water• WVR => coefficients used by correlator software to correct for the path-length variations due to atmosphere

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TELCAL subsystem 6

TelCal and the other ALMA subsystems

TELCAL

CONTROL

CORRELATOR

EXECUTIVE

ARCHIVE

Results(ASDM)

Results (ASDM)

Start/stop

Metadata (ASDM)

Correlator data

Totalpower data CONTROL(DataCapturer)

• ACS (Alma Common Software) infrastructure based on CORBA (components, containers, events,…)

• AudioVideo streams for binary data transfer

• ASDM format for input (metadata) and output (results=ASDM containing Calxxxx tables)

WVR data

CONTROLantenna adjust.

quicklook

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TELCAL subsystem 7

Conclusion

TELCAL – CASA relationship

• Calibration code of TelCal available in casa tasks (see J.C Roche presentation)

• casa is a useful tool for the TelCal software development :– casa script developed to test the validity of the path delay correction using WVR

data– plotms can be used to analyze the content of ALMA datasets

• Reduction of IRAM interferometric data with casa :– 2 fillers : PDBI format -> ASDM and ASDM->MS– First goal : prepare astronomers for CASA inside IRAM ARC (ALMA Regional

Center) node– Second goal : use specific features of CASA (polarimetry, …) not implemented in

IRAM data reduction software (gildas)