[daip] ANTAB problem reading WX table with 2001 data.

[R. Craig Walker]

I tried running APCAL on 43 GHz VLBA data taken in 2001.  I was trying
to fit the opacity.  For every station, I got a message of the form:
APCAL1: REAWX: *** NO TEMPS FOUND IN WX TABLE FOR ANT 8, LEFT AT 0 ***
INVERS is set to 1 and there is a WX table with valid looking
temperatures for all antennas.  So something is wrong, presumably in
reading that table.

I compared the table to a modern one from data taken last year.  I see
a couple of differences, but I don't know if they will confuse the
reader.  The old table has 10 columns while the new one has 11.  The
missing one in the old table is the subarray (not sure why the weather
data should depend on subarray, but oh well).  The other difference is
the column heading for temperature.  The old file had "TEMPE" while
the new one has "TEMPERA".

I plotted the data with WETHR, and that found the temperature data,
although it took some considerable staring at the help file to figure
out how to get it not to edit data.  I suggest a more obvious switch
than just OPTYPE='MULT'.  Using display programs that can alter your
data if you put in inappropriate parameters is always a bit scary to
me.  VPLOT is another example.

WETHR worked and there are reasonable looking temperatures (~63
points) for most stations.  Unfortunately there are some suspicious
data where various parameters step a lot (eg pressure from 650 to 980
mbar at NL) That's in the WX table according to PRTAB, so it is not
WETHR's fault.  Sometimes I think I shouldn't look at my data!  The
issue is not there in the weather data plots from tsm (outside AIPS),
so it appears to be a calibration transfer issue.

To salvage that, I ran VLOG and and tried using the resulting weather
file.  I see that there is a warning in the VLOG.HLP that the cal.vlba
file is based on the legacy system.  That will be changing in the
rather near future so we should remember to update the HLP file.

VLOG worked, after some fumbling, and produced an external WX table.
APCAL is happy with that and does give answers that are somewhat
different from what it got guessing values when it couldn't use the WX
table.

So the main thing I'm reporting here is that APCAL does not seem to be
able to read the old (2001) WX table even though PRTAB and WETHR can,
and APCAL can run properly with the same inputs when given an external
file.  If the cause is not obvious, I could produce a test file, but
the data are at home so that will take jumping through a few hoops.

Cheers,

Craig


---------------------------------------------------------------------
    R. Craig Walker            Array Operations Center
    cwalker at nrao.edu           National Radio Astronomy Observatory
    Phone  575 835 7247        P. O. Box O
    Fax    575 835 7027        Socorro NM 87801   USA
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