[daip] CLCOR position shifting question

[Leonia Kogan]

Mark

As I understand:

You run CLCOR with correction of the source position by 1as.
You use the virgin CL table (GAINVER) to correct. So the corrected table 
will include single band delay, rate, and multi band delay ... which 
CLCOR calculates based on the Geometry.
CLCOR puts the same value for the single- and multi- band delay.

Now you run FRING with DOCALIB = 1 APARM(5) =2 and find the solution for 
delays and rates. You expect to see the solutions identical to the CLCOR 
result but with opposite signs. CORRECT?

FRING finds solution for multi band delay fitting by least square the
value into set of single source delay or something like that.
I have never understood it :(

So it can easy find zero solution for multi band delay, if the 
instrumental delays (single band delays) are different for different IFs.

So I'd recommend you to compare rates (you did it) and single band 
delays instead of multi band ones, using APARM(5)=1 in FRING

You wrote:

 > So, the question: does CLCOR/ANTC put in frequency dependent phase
 > shifts that would correspond to the desired changes in multi-band
 > delays when one shifts source positions?

The answer is YES but it would correspond to the desired single band 
delay, which apply to the multi band delay also.


Leonia





Mark Reid wrote:
> Leonia,
> 
>    I have a question about CLCOR and shifting source positions.
> I am writing a program to take multi-band delays and rates and solve for 
> source position offsets.
> 
> For a quick check on my code I took some well calibrated data (meaning 
> the multi-band delays and rates are near zero) and shifted the positions 
> of some sources by about 1 arcsecond (with CLCOR/ANTC).   Then I reFRING 
> to get new multi-band delays and rates.
> 
> When I fit the new delays and rates for source position shifts, I find 
> it works for the rates, but not for the multi-band delays. Specifically, 
> it looks like the multi-band delays are pretty small.
> 
> So, the question: does CLCOR/ANTC put in frequency dependent phase 
> shifts that would correspond to the desired changes in multi-band delays 
> when one shifts source positions?
> 
> Thanks,
> Mark
> 
> PS: regarding the ionospheric code you put into CLCOR a while ago, we 
> haven't forgotten about it.  We've been temporally sidetracked getting 
> our huge VLBA project started.  However, a postdoc in China and I are 
> just getting back to testing it.
> 
> 
> 
> -------------------------------------------------------------
> Mark J. Reid                 Phone: 617-495-7470
> Harvard-Smithsonian CfA      Fax  : 617-495-7345
> 60 Garden Street             Email: reid at cfa.harvard.edu
> Cambridge, MA 02138, USA     Web  : www.cfa.harvard.edu/~reid
> -------------------------------------------------------------