[daip] Question about LOCIT

[Eric Greisen]

Dayton Jones writes:
 > Hi.  Thanks to Eric we now have a version of LOCIT that runs 
 > without complaint on the single-polarization from our JPL test 
 > interferometer.  However, I now have a question about interpreting 
 > the results.  The expected errors in our interferometer baselines 
 > are several cm (possibly as large as a few tens of cm).  LOCIT 
 > produces antenna position corrections that are sub-cm, with sub-cm 
 > uncertainties.  It seems implausible that the true antenna position 
 > correction could be so small.  Is there an implicit assumption in 
 > LOCIT that the a priori antenna positions are known to less than 
 > one wavelength (about 4 cm in our case)?  

LOCIT has not been tested in the mutiple wavelengths off regime nor in
the regime of only 3-4 antennas.  I would distrust its answers and
certainly any estimates of error.  Try applying its corrections to see
if your phases behave better or not.  I think we zero in a new VLA
station by other means and only use LOCIT when we know about where it
is.

I am Cc'ing rperley since he is the expert in this area.

Eric Greisen