[daip] [!13162]: AIPS - DTSIM, still not ok

[Thomas Krichbaum]

DTSIM, still not ok
-------------------

           Ticket ID: 13162
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/13162
                Name: Thomas Krichbaum
       Email address: tkrichbaum at mpifr-bonn.mpg.de
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Eric Greisen
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template group: Default
             Created: 13 December 2018 04:54 PM
             Updated: 17 December 2018 07:32 PM
           Reply due: 19 December 2018 07:32 PM (2d 0h 0m)
      Resolution due: 08 September 2021 12:00 AM (995d 4h 27m)

yes, DPARM(4)= 0 looks ok to me. We want to simulate data which are as
close as possible to what we get from a 'real' pol-VLBI experiment. In
such an experiment the 1st thing we do is always to apply the
parallactic angle correction (PANG in CLCOR) and then fringe on top of
this. So in the final data we don't expect any parallactic angle
dependence of I, Q, and U. DTSIM now seems to do this.

I still wonder why I could not recover the D-terms from a simulated data
set using PCAL, when I use the same polarisation model as input? I will
do some more checks later.

for DPARM(4)=1 I do see strong parallactic angle effects in the cross
hands, as expected. But in the parallel hands the phase rotation seems
to be less pronounced. Wouldn't one expect that both are similar ?
Anyhow DPARM(4)=1 is not so important for me right now.

Thanks again for help !

regards Thomas

On 12/15/18 1:41 AM, Eric Greisen wrote:
> Yes - in fact the old code is correct.  RR and LL do wander apart
> in phase due to the difference in parallactic angle between the
> 2 telescopes.  I suspect that the DiFX correlator "corrects" this
> with a phase shift.  I have added to the old code two corrections
> 1. We must do this whether or not the D terms are non-zero
> 2. By default, I will correct for the parallactic angle (a la CLCOR)
> so that a point source at the origin has a constant I visibility.  To
> get the actual observed vis one can set DPARM(4) > 0 and then
> the code does not do the correction.
> 
> Note that I also changed to polarization type to APPROX from
> VLBI.  I am not sure what the latter does.
> 
> Eric Greisen
> 
> 
> Ticket Details
> ------------------------------------------------------------------------
> Ticket ID: 13162
> Department: AIPS Data Reduction
> Type: Issue
> Status: Open
> Priority: Default
> 
> Helpdesk: https://help.nrao.edu/index.php?

-- 
Dr. Thomas P. Krichbaum
Max-Planck-Institut fuer Radioastronomie
Auf dem Huegel 69
D-53121 Bonn / Germany

Mail: tkrichbaum at mpifr-bonn.mpg.de
Tel.: (Germany +49)-228-525-295
Web : http://www.mpifr-bonn.mpg.de/research/vlbi


------------------------------------------------------
Staff CP:  https://help.nrao.edu/staff
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listmgr.nrao.edu/pipermail/daip/attachments/20181217/501505e1/attachment.html>