[daip] DEFLG

[Eric Greisen]

Naveen Yadav wrote:
> Hi
> 
> I want to use the task 'DEFLG' for removing scintillation corrupted 
> data. I think I understood from the explanation in the help file how it 
> would work  for a
> phase calibrator. But can it flag data for target source whose phase is 
> not expected to be steady? How will the algorithm work in that case?
> Can you please elaborate on the working algorithm of this task?
> 

I often suggest that it is good for students to read the code itself to 
see what it is doing.  Students should try to do some of this for 
pedagogical reasons.  It is found at $TST/Q/PGM/NOTST and, being 
Fortran, not too difficult to read.

You have identified, however, a limitation of this task.  Its purpose is 
to identify periods in which the atmosphere/ionosphere (high/low 
frequencies) is so unstable that the calibration observations are not to 
be trusted.  The DOALL adverb does allow for carrying flags from one 
scan through another (target) scan to the next calibrator.  You may have 
to do this by hand.

Note that DEFLG is an old task, not much used in practice.  SNFLG is 
useful to identify, on a baseline basis, those calibration scans between 
which there are excessive phase jumps due to atmospheric instability.
The new task RFLAG is useful for identifying unstable data - usually RFI 
- and removing it.  This task works on calibration and target sources 
although it may need different adverb values for the two.

Eric Greisen