[daip] forwarded message from Mark Reid

Mon Sep 23 12:22:45 EDT 2002

Mark,

I'll be a person (probably) who will add the new option to CLCOR.
I am sorry to inform you that I can not start doing that emmidiately,
because I am very busy with other activity. I hope to start it in three
- four weeks.

Right now I have found a time to infer more precise formulae for delay 
at the given elevation (ZA) having had the vertical delay.

These formulae consider a model of the atmosphere: the homogenios belt 
around the Earth with the belt thick equaled to the vertical delay.

The formulae are full precise in comparison with the aproximate 'cosec(el)'
for the plane model of the atmosphere.

My question is:
The actual model of the atmosphere can be more complicate than the homogenious 
sphere belt around the Earth and can be variable in time. 
Do you still belive that the sphere belt around the Earth describes the
atmosphere effect with enough accuracy?

Thanks

Leonia
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From: Mark Reid <reid at cfa.harvard.edu>
To: egreisen at cv3.cv.nrao.edu
cc: Andreas Brunthaler <brunthal at mpifr-bonn.mpg.de>
Subject: Request for help on CLCOR
Date: Fri, 13 Sep 2002 15:37:54 -0400 (EDT)

Eric,

We are doing astrometric VLBA projects, trying to measure
the proper motions of galaxies.  This requires correcting
for small errors in the atmospheric model of the correlator.
We use multi-band delays and fringe rates on sources of known
position to solve for the error in the vertical delay through
the atmosphere for each station as a function of time.
Now, we would like to be able to input these vertical delay
errors and have CLCOR update a CL table for the resulting
phase shifts.

Currently, there are two problems with CLCOR:

  1) One must input a full atmospheric model, instead of
     small adjustments.  We have no good way to get this 
     information from the correlator residuals.

  2) One must re-run CLCOR for each antenna, one at a time.
     For 10 stations this is very clumsy.

So, could you change CLCOR to do what we need?

This would involve the following:

1) Reading a text file containing the following:

    Station_1       Time_1        Vertical_delay_error
    Station_1       Time_2        Vertical_delay_error
    Station_1       Time_3        Vertical_delay_error
    Station_2       Time_1        Vertical_delay_error
    Station_2       Time_2        Vertical_delay_error
      .
      .
      .

2) Interpolating the Vertical_delay_errors in time

3) For each station, calculating expected delay changes,
   essentially by scaling by sec(ZA).  (We have slightly
   better "mapping functions" and could supply them to
   you.)

4) Adding the changes to a CL table.

Thanks for considering this request.

Mark

- -------------------------------------------------------------
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  : cfa-www.harvard.edu/~reid                  
- -------------------------------------------------------------

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