[daip] [!10581]: AIPS - Unexpected results from VLBACCOR on VLBA data

[NRAO Helpdesk]

Amy Mioduszewski updated #10581
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       Staff (Owner): Amy Mioduszewski (was: -- Unassigned --)

Unexpected results from VLBACCOR on VLBA data
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           Ticket ID: 10581
                 URL: https://help.nrao.edu/staff/index.php?/Tickets/Ticket/View/10581
           Full Name: Tanmoy Laskar
               Email: tlaskar at cfa.harvard.edu
             Creator: User
          Department: AIPS Data Reduction
       Staff (Owner): Amy Mioduszewski
                Type: Issue
              Status: Open
            Priority: Default
                 SLA: NRAO E2E
      Template Group: Default
             Created: 25 June 2017 04:13 PM
             Updated: 25 June 2017 04:13 PM
                 Due: 28 June 2017 02:42 PM (2d 0h 0m)
      Resolution Due: 04 July 2017 12:00 AM (7d 9h 17m)


Hello,

I am attempting data reduction for VLBA project BL230 using the AIPS VLBAUTIL procedures, and have run into a curious issue while attempting to correct for errors in the sampler threshold using ACCOR. The steps taken were:
1. Load data into AIPS using VLBALOAD
2. Correct the Earth Orientation Parameters using VLBAEOPS (CL1)
3. Remove delays due to ionospheric dispersion using VLBATECR (CL2)
4. Decimate the data by a factor of 10 for processing using AVSPC (CHANNEL=10) and selecting only calibrator sources (CL3)
5. Attempted to derive sampler corrections using VLBACCOR.

This last step generates SN1 & CL4. Upon plotting the resulting SN table, we find our solutions to be milligains ~ 2300 (see attached plot), regardless of the time range or source selected and solution interval employed. The expected values of the gain is order unity (milligain ~ 1000 rather than ~ 2300), and I am concerned about these differences. Is this a significant issue, and if so, what must be done differently?

Thanks for your help,
Tanmoy Laskar
Jansky Fellow
NRAO & Berkeley

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