[daip] [!9298]: AIPS - Suggestion to change behaviour of keyword antennas in AIPS task IMAGR

[Eskil Varenius]

Eskil Varenius updated #9298
----------------------------

Suggestion to change behaviour of keyword antennas in AIPS task IMAGR
---------------------------------------------------------------------

           Ticket ID: 9298
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/9298
           Full Name: Eskil Varenius
               Email: varenius at chalmers.se
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): -- Unassigned --
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 19 November 2016 12:25 PM
             Updated: 19 November 2016 12:25 PM
                 Due: 24 November 2016 12:00 AM (4d 11h 35m)
      Resolution Due: 30 November 2016 12:00 AM (10d 11h 35m)



Hello,

A few years ago I discovered that the "antennas" keyword in the task IMAGR works differently to other tasks in AIPS, e.g. CALIB. Every now and then, I run into confused colleagues who make mistakes when calibrating and imaging their data as they get confused by this particular keyword. Allow me to explain the situation through an example.

Imaging a data set with five antennas, 1,2,3,4,5. In, for example, the task CALIB I can de-select antenna 4 in two ways. Either I specify antennas = -4, or I specify antennas = 1,2,3,5. Both ways give identical results, and this is also what most people find intuitive in my experience.
In IMAGR, it is different. If I want to deselect antenna 4, I can do so in these two ways:
a) specify antennas = -4
b) specify antennas = 1,2,3,5 AND baselines = 1,2,3,5.
If I just specify antennas, without setting the baseline keyword, some baselines are still included to antenna 4. This has confused many persons.

I suggest to do one of two things.
1) Change the behaviour of the IMAGR task, so that it works the same way as CALIB.
2) Clarify the documentation of iMAGR with a very clear explicit example, and pointing out the differences to other AIPS tasks. Preferably with capital "WARNING:" written early in the text. This would save many people a lot of trouble.

The main problem, as I see it, is that people sometime find bad antennas in their data. They think they make an image without those antennas, while in fact they are including some of the data because they misunderstand the syntax in IMAGR. This means that the results they present are not what they think, and in the worst case they may be severely worsened by the bad antennas included.

Best regards,
Eskil

------------------------------------------------------
Staff CP:  https://help.nrao.edu/staff