Known Issues

ALMA Restores

The ALMA Restores are only available for 12m and ACA data that were pipeline calibrated in Cycle 5and beyond (select Cycle 4 datasets processed in Cycle 5 may also be available). Data that were manually calibrated cannot be restored by this process and require a full download and execution of the calibration script. Single-dish (Total Power) datasets are also not supported for restoration at the present time.

Certain pipeline-processed projects that were sent for manual imaging can be restored via this process, but some additional flags may have been added during manual imaging and these will not be applied to the restored dataset. These flags may not be of significant consequence, but users should check if flagdata commands are present in the *scriptForImagingPrep.py included with the auxiliary package from the ALMA data archive.

What to do if your ALMA Cycle 5 restore is failing?

When attempting to restore ALMA datasets from Cycle 5 (typically those with a project ID like 2017.1.XXXX.S), the restores may fail when using the default CASA version 5.6.2. If a failure is encountered, the restore should be resubmitted, but with CASA version 5.1.1-5 selected from the drop down box. This workaround is required because the data are imported to a measurement set differently in CASA 5.4.2/5.6.2/6.1.2 versus the CASA version 5.1.1-5 that was used for processing. This prevents the flags from being reapplied properly. In the future, the restore feature will automatically select the proper version of CASA for restoration.

ALMA User-Defined Imaging

ALMA Cube Imaging runs a modified recipe of the ALMA imaging pipeline to produce cubes with custom channel width, overall spectral width, and velocity or frequency-defined channels. Cleaning uses the same automasking procedure as the ALMA Imaging Pipeline and low signal-to-noise emission may not be fully encompassed within a clean mask. Imaging results for Cycle 5 data may differ from the archived products because ALMA Cube Imaging uses the most recent imaging pipeline and incorporates the recent improvements to functions such as continuum finding and automasking.

The same limitations of the restorations also apply. This also means that those ALMA Cycle 5 datasets that cannot be restored in CASA 6.1.2 also cannot be imaged. This is because imaging requires CASA 6.1.2 or later and it is not currently possible to restore with one version of CASA and image with another.

At present, the archive does not allow ingestion of more than one cube with the same combination of MOUS and source. These jobs will fail, even if a different spectral window is requested for imaging compared to the initial ingest,

Why Do I Not Get the Angular Resolution I Requested?

The modified ALMA imaging pipeline recipe uses a pipeline task called hifas_imageprecheck to set the appropriate tclean settings (robust and uvtaper) to get an angular resolution as close as possible to the requested resolution. Based on the data being imaged, there will be a maximum (smallest beam) and minimum (largest beam) angular resolution allowed by the pipeline. So requests for a beam smaller or larger than the limits will simply be set to the appropriate limit for a large or small beam.

VLA Restores

The VLA data and calibrations within the archive have not undergone rigorous Quality Assurance and flagging for observations executed prior to June 17, 2019 and even after this point not all data will have Quality Assurance. The flux calibration accuracy is not likely to be better than 10% and uncertainty could be higher, especially at frequencies > 20 GHz. Furthermore, portions of the science target data may have significant RFI that was not flagged by the pipeline and further flagging may be required to produce optimal images, especially for frequencies < 20 GHz.

Spectral line detection and imaging from restored datasets should not be regarded as science quality. The calibration pipeline uses RFI flagging throughout the spectral range that will flag spectral line data, also the statistical weighting of visibilities is optimized for continuum and will downweight emission lines. Users aiming to do spectral line science are advised to recalibrate the data using the pipeline recipe modified for spectral line data.