Modifying Visibility Datasets

The task uvedit allows you to apply some specific sorts of corrections or modifications to your visibility dataset. For example, there may be a clock error that needs fixing, or the antenna coordinates were wrong so that u and v need to be recomputed, or the phase centre was wrong requiring a phase rotation and u and v recomputation. Note that any data not selected are copied to the output dataset unchanged.

The following example changes the RA phase centre by 10 seconds of time and also corrects a delay error of -3 ns on antenna 2 (by adding a phase gradient across the band). uvedit has the option to turn off the recomputation of u and v which might otherwise be done (options=nouv). This can be useful for say, entering a delay change (which does not need u and v to be recomputed) because Miriad does not compute u and v as accurately as the on-line ephemeris routines.

UVEDIT
vis=multi.uv	Input visibility dataset
source=0823-500	Specify source; unset means all
antpos	No change to antenna coordinates
dantpos
ra=10	Move RA phase centre
dec	No change to DEC
time	No clock offset
delay=0,-3,0,0,0,0	Delay error on antenna 2
out=multi_corr.uv	Output visibility dataset
options	Do the works

The task uvredo also `edits' a visibility dataset. Unlike uvedit, however, it only modifies ancillary data in the dataset that are derivate from other information. For example, it can recompute the sky feed angle (``chi'') and velocity information.