[daip] amplitude in AIPS

[Shen Zhi-Qiang (NAO VSOP)]

To whom it may concern,

I have a question regarding weighting or the error of the visibility. 
What are those amplitudes immediately after the data is loaded into 
AIPS using FITLD (probably plus ACCOR)? Are they exactly the same as 
the outputs from the correlator, i.e. the correlation coefficients? 
If not, how are they related? I wonder what is the noise level for 
each visibility. Seems they are all set to the unity since the weighting 
for the visibilities is ~1.0 after FITLD. If so, how can we estimate the SNR? 

The reason that I am asking above questions is that we are developing
a method to deal with the amplitude closure. For this, any amplitude 
calibration in AIPS is not necessary and the amplitude directly from 
the correlator (i.e., the correlation coefficient) is preferred. But
of course we need to perform fringe fitting in AIPS before exporting
the data. For the correlation coefficient, the noise can be determined
from the data sampling. So, I want to know if AIPS FITLD can keep the
correlation coefficients or how the amplitudes in AIPS connect to the
correlator outputs.

Looking forward to hearing your answer and suggestions if any.

Cheers,
Zhiqiang Shen