VLBA AIPS-to-CASA Primer
This 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.
VLBAUTIL Procedures
This section 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 | |
| CLCAL | applycal |
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 |
Parallactic Angle Correction
| VLBAUTIL Procedure | AIPS Task(s) | CASA Task(s) |
|---|---|---|
| VLBAPANG | CLCOR opcode 'pang' |
set parang=True in applycal, fringefit, and bandpass |
Additional Tasks
| AIPS Task | CASA Task |
|---|---|
| SPLIT | split |
| IMAGR | tclean |
| CALIB | gaincal |
| POSSM | plotms |
| SNPLT | plotms |
| UVPLT | plotms |
| UVFLG | flagadata |
| FITTP | exportuvfits or exportfits |
