VLBA AIPS-to-CASA Primer

The primer (or "cheat sheet") is intended to help those VLBA users who are used to calibrating and imaging their data in AIPS transition to CASA.

It presents the AIPS VLBAUTIL procedures, the AIPS task(s) associated with those procedures, and the equivalent CASA task(s) and/or tool(s).

Loading Data

Both AIPS and CASA need to take the FITS-IDI file and convert it into a format they can use. AIPS uses the UVDATA format, and CASA uses the Measurement Set (MS) format.

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBALOAD	FITLD	importfitsidi

Observation Summary

Printing a summary of the observation is often useful for identifying the fringe finder, bandpass calibrator, phase reference calibrator, and science target. It is also useful for locating a good time range to use for the instrumental delay correction.

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBASUMM	PRTAN	listobs
	LISTR optype 'scan'

Total Electron Content Correction

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBATECR	TECOR	no equivalent CASA task yet

NOTE: Do not use the tec_maps tool with VLBA data. It does not work properly for VLBI observations.

Earth Orientation Parameter Correction

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBAEOPS	CLCOR opcode 'eops'	no equivalent CASA task yet

Sampler Corrections

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBACCOR	ACCOR	accor
	SNSMO	smoothcal

Instrumental Delay Correction

NOTE: Many VLBA users are likely familiar with the VLBAUTIL procedure VLBAPCOR and the associated AIPS task PCCOR, which use the pulse-cal tone information from the VLBA to correct for the instrumental delay. CASA does not currently have a means of working with the pulse-cal tones, so it cannot use this functionality. It is an area of active development for the NRAO and JIVE CASA software engineers and scientists.

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBAMPCL	FRING	fringefit
	CLCAL	applycal

Global Fringe Fitting

The VLBAUTIL package contains 2 methods for doing the global fringe fit:

• VLBAFRNG does a fringe fit on every source in the observation
• VLBAFRGP does a fringe fit on the phase-reference calibrator(s) and transfers those solutions to the science target(s)

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBAFRNG or VLBAFRGP	FRING	fringefit
	CLCAL	applycal

Bandpass Correction

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBABPSS	BPASS	bandpass

Final Amplitude Calibration

VLBAUTIL Procedure	AIPS Task(s)	CASA Task(s)
VLBAAMP	ACSCL	accor
	SNSMO	smoothcal
	CLCAL	applycal
	APCAL	gencal
	CLCAL	applycal