EVNMERGE

EVNMERGE translates data from the "EVN120" format of the European VLBI
Network  into  the  Caltech MERGE format.  The EVN120-format file must
first be copied from tape onto disk.

     To run the program use the command EVNMERGE:

$ EVNMERGE


     The program asks for

     1.  Output file name, for the new MERGE file (eg 3C84.MRG).

     2.  Control  parameters:   free-format,  ended   with   /.    The
         parameters  are the same as for MERGE; the important ones are
         SOURCE, STATIONS and TITLE.  The source name (SOURCE) [up  to
         8   characters]   and   the  station  names  (STATIONS)  [two
         characters  each]  must   match   those   recorded   in   the
         EVN120-format  file; you may want to use parameter NEWSTAT to
         provide different station names  for  the  output  file  (see
         MERGE).

     3.  Input file names (name of the EVN120-format file).  More than
         one EVN file can be merged into the same output dataset.

     4.  Whether  the   amplitudes   are   uncalibrated   (correlation
         coefficients) or calibrated (correlated flux density in Jy).



The EVN120 format

The EVN120 format is a text file, with one record  of  120  characters
for  each visibility measurement.  Program EVNMERGE uses the following
fields in each record:

Columns Format  Description

1:3     I3      UT day number
4:6     I3      UTC hours
7:9     I3      UTC minutes
10:14   F5.1    UTC seconds
15:19           - ignored -
20:26   F7.3    Amplitude (correlation coefficient x 10^6, or
                        correlated flux density in Jy)
27:32   F6.3    Standard error on amplitude
33:38   F6.1    Phase (degrees)
39:43   F5.1    Standard error on phase
44:68           - ignored -
69:70   A2      First station name
71:72   A2      Second station name
73:80   A8      Source name
81:120          - ignored -

EVNMERGE                                                          Page 2


     The EVN120 file should  also  contain  header  records  supplying
additional parameters.  These are identified by a code in columns 1:4:
RUN (reference time  and  GAST);  SOU  (source  coordinates);  or  ANT
(station  coordinates).   If these records are missing, the parameters
must be entered in the merge-file header using VLBEDIT (see below).


Warnings


     1.  The time recorded in the EVN120 file is assumed to be the UTC
         at the middle of the integration.

     2.  EVNMERGE changes the sign of the phase to match  the  Caltech
         convention.

     3.  It  is  assumed  that  all  necessary  corrections  (retarded
         baseline,  etc.)  have  been  applied  to  the phases so that
         correct closure phases can  be  obtained  simply  by  summing
         around triangles.

     4.  If the EVN120 file does  not  contain  the  necessary  header
         parameters  (source  and  station  locations, etc.), EVNMERGE
         will issue a warning ("no data found") for each station  that
         has  no coordinates.  It will be necessary to add the missing
         parameters to the MERGE-file header using VLBEDIT, specifying
         parameters  RA, DEC, RAP, DECP, FLUX, X, Y, Z, YEAR, DAY, UT,
         GST, and FREQ.  Note that it is vital  to  have  the  correct
         year  (YEAR), antenna coordinates (X, Y, Z), precessed source
         coordinates  (RAP,  DECP),  frequency  (FREQ),  and  GAST  at
         reference time (GST).  The choice of reference time (DAY, UT)
         is arbitrary:  usually 0h UT on the first day of  observation
         is  used.   The  source coordinates (RAP, DECP) should be the
         geocentric apparent position at  this  epoch.   Use  LIST  to
         verify that all the header parameters are correct.



Limitations

This version of EVNMERGE accepts the EVN120 format defined in  a  memo
from   Lars   B. Baath  dated  13-Apr-1984.   It  has  not  been  very
extensively tested.  The program should be used  with  care,  and  the
resulting  MERGE  file  should  be checked very carefully for possible
errors.


History

Version 1.0:  1984 Jun 5 - T.J. Pearson.
Version 2.1:  1990 Feb 1 - revised for Unix (Sun/Convex).