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The ALMA TelCal subsystem

The ALMA TelCal subsystem. Dominique Brogui è re , Institut de RadioAstronomie Millim é trique (IRAM) Casa Developers meeting - 12/05/2010. Introduction. TELCAL is the on-line calibration software for the ALMA array

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The ALMA TelCal subsystem

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  1. The ALMA TelCal subsystem Dominique Broguière , Institut de RadioAstronomie Millimétrique (IRAM) Casa Developers meeting - 12/05/2010

  2. Introduction • TELCAL is the on-line calibrationsoftware 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 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, … 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 TELCAL subsystem

  5. Calibration engines 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 : 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 • 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 TELCAL subsystem

  6. TelCal and the other ALMA subsystems EXECUTIVE CONTROL antenna adjust. Start/stop CONTROL (DataCapturer) CONTROL TELCAL Totalpower data Results(ASDM) Metadata (ASDM) quicklook CORRELATOR Correlator data ARCHIVE Results (ASDM) WVRdata • 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) 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) TELCAL subsystem

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