[daip] TY table entries associated with wrong data set.

[Craig Walker]

It is VLBA only data.  And the time stamps are probably correct.  I 
think the reason I'm seeing the problem is that I have 4 minute scans. 
The Tsys measurements are for 2 minutes so 2 nominally just fit.  But it 
looks like there is commonly a third measurement that gets flushed out 
right at the end of the scan.  It is probably a very short integration 
and has a time stamp very close to the scan end time.  In fact, it is so 
close to the end time that it falls after the mean time of the last data 
point - which is what INDXR uses for the scan end, even though half of 
the last data point comes from data after that time.  Thus confusion, 
and a real mess for me.  Clearly, in splitting up the file, no attention 
is paid to the start time of the scan, or these particular records would 
just go to the bit bucket.

It's amazing how much pain we've had over the years trying to get 
calibration data associated with the right scan.  If from the start we 
had put some sort of scan association in the data records - starting in 
the antenna monitor data set, we could have avoided all this.  Is it too 
late to think about getting this right in the future?  In any case, 
perhaps INDXR should have something equivalent to ANTAB's OFFSET to push 
the scan boundaries out by at least half the integration time so it 
would encompass all of the time of the scan boundary records, not just 
to the mean times.  Of course, there is also the issue of how to deal 
with the EVN style calibration data that is intentionally measured 
outside the actual scan time.  Is that still done with OFFSET?

Cheers,

Craig


Lorant Sjouwerman wrote:
> On Wed, 9 Jan 2008, Craig Walker wrote:
> 
> 
> #Anyway, this would really screw up my calibration so I'm going to go with the
> #data loaded from the TSM file.  But some sort of tolerance or something needs
> #to be built into calibration transfer.
> 
> If this is vlba only data, then the tsys entries come directly from the 
> correlator jobs, ie from the monitor data, and unless FITLD changes time 
> stamps, this needs to be addressed in correlator software - nothing that 
> the preprocessing is doing with the time stamps or the OFFSET parameter
> 
> 
> Regards,
> 
> Loránt Sjouwerman - Scientific Services - lsjouwerman at nrao.edu
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     R. Craig Walker            Array Operations Center
     cwalker at nrao.edu           National Radio Astronomy Observatory
     Phone  505 835 7247        P. O. Box O
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