This task serves to convert a CASA visibility file (MS) into an ALMA or EVLA Science Data Model dataset. They are mostly identical and mostly use the general SDM and ALMA ASDM terms interchangibly. A description of the SDM format can be found here

The main purpose of creating this task was to (a) enable the creation of simulated ASDMs and (b) facilitate the testing of (A)SDM to MS conversion. The user may think of other purposes.

The sbduration parameter controls the number of execution blocks (EBs) into which exportasdm subdivides the visibilities from your input MS. If the total observation time in the MS is shorter than what is given in sbduration, a single EB will be created.

Note concerning ALMA data: exportasdm presently is not able to export from MSs containing WVR data. If you attempt to export such an MS, you will receive an error message saying that you can only export data of processor type "CORRELATOR". It will also give you the list of SPWs which contain CORRELATOR data. You will then have to split out these SPWs using the task split and run exportasdm on the resulting MS.

Also EVLA data can be exported. Note here that exportasdm does not produce online flags and that a subsequent re-import of the data must be done with online=False. Also, importevla will only work on your ASDM if you have exported it with apcorrected=False (the default), as shown in the following example:

# Import EVLA SDM
importevla(asdm='xosrosdm', vis='')

# Export ASDM, with apcorrected=False
exportasdm(vis='', asdm='xosroasdm2', apcorrected=False)

# Re-import ASDM, with online=False
importevla(asdm='xosroasdm2', vis='', online=False)