# extracting visibility information from CASA measurement set

I am trying to export the UV wavelengths, visibilities and weights from a measurement set in CASA, but I haven't been able to find the right commands to do this.

'exportuvfits' might be what I am looking for, but I can't find a clear explanation of what this format really is.

Any CASA users out there that can help me?

• Have you tried it to see what happens? If so, can you add to your question a description of the results and if they are not suitable, what you need instead? Thanks!
– uhoh
Jan 30 at 0:41
• What is CASA? More details/links please. Jun 14 at 12:23
• @ProfRob CASA is the Common Astronomy Software Application, and is used for data processing of ALMA/VLA data (casa.nrao.edu) Jun 21 at 9:47

UVFITS is a file format that has a history of use in AIPS, so it likely won't be much use here.

It looks like an easy way to get what you're looking for is to use the export_uvtable task of uvplot (see documentation here). Since uvplot is not a standard CASA library, you'll have to install it with pip from within CASA (if you are using a mac and CASA 5 or above):

pip install uvplot


Then run split to isolate the visibilities you wish to extract, e.g.:

split(vis='FULL.ms', field="0", spw="0~2", outputvis="TEST.ms", datacolumn="data")


And finally run export_uvtable

from uvplot import export_uvtable
export_uvtable("uvtable.txt", tb, vis="TEST.ms", datacolumn="DATA")


The resulting uvtable.txt file contains columns of u, v, Real(V), Im(V), and weight.

• Thank you for your answer - this looks like a good way to achieve what I was looking for. In the meantime, I was able to write some python within CASA to do what I needed (with some help from a colleague). Jun 21 at 9:49