Description

Subtracts model visibilities from the corrected visibility data in a MeasurementSet.

This task subtracts the model visibilities in the MODEL_DATA column of a MeasurementSet from the corrected visbilities in the CORRECTED_DATA column. The MODEL_DATA column can either be the scratch column or a virtual one. The residuals after subtraction are placed in the CORRECTED_DATA column. If the parameter reverse is set to True, the process is reversed and the model will instead be added to the corrected data. The DATA column is left untouched. If the MeasurementSet has no CORRECTED_DATA column, one is created and the content of the DATA column is copied into it ahead of the uvsub process.

NOTE: uvsub does the subtraction over the whole MS. The model visibilities are usually populated by the tasks clean/tclean, ft and setjy. If only a subsection of the MS was used in these tasks (e.g., when selecting field or spw in clean or ft), then only this subset of model visibilities will be populated and the uvsub operation will give expected results only for this subsection of the MS. The remainder of the MS will get the CORRECTED_DATA added/subtracted with whatever was there originally in the MODEL_DATA column (on initialization, the model visibilities are 1 for parallel hand and 0 for cross hand).\

WARNING:  Currently, uvsub will not work if the frequency axis is different between the MS file the model is derived from and the MS file you are subtracting from. Please use cvel2 to regrid the frequency axis of the MS to match that of the model.

See also the CASA Docs chapter pages on Subtracting and Adding Model Visibilities.

 

Parameter descriptions

vis

Name of input visibility file (MS).

reverse

Reverse the operation (add rather than subtract). Default is reverse=False.