[daip] negative elevation values: BL149CC

[Eric Greisen]

Yuri Y. Kovalev wrote:
> Dear colleagues,
> 
> I am writing you again about AIPS / VLBA data problems during American 
> holidays. There must be some reason why I am so "lucky" during these 
> days. Anyway, here it comes.
> 
> AIPS ver 31DEC08.
> MOJAVE 512 Mbps experiment BL149CC.
> Problem: I got negative elevation values.
> To track it down I have loaded just one pass (using FITLD) - 
> BL149CC_1_FPOL4IF8MHZ16CH_15.3256GHZ00 (taken from the NRAO archive) 
> than have plotted elevation versus time for the refant 2 (FD). You can 
> see results attached. Any ideas what is wrong and how to fix it?
> 
> Two comments:
> 
> I have discovered this problem while doing APCAL with opacity 
> correction. Opacity correction was doing strange things which pushed me 
> to check the elevation values. After discovering the problem I have 
> deleted everything, loaded one pass and the problem was there.
> No VBGLU involved.
> 
> To check if this is my local AIPS issue I have loaded into the same AIPS 
> one of my recent BK150 U-band datasets 
> (VLBA_BK150K_FPOL4IF8MHZ16CH_15.3495GHZ03.uvfits) and everything looked 
> fine (positive meaningful elevation values).

You are indeed unlucky.  There are actually two problems - the use of 
the uvfits files means that you are getting 31DEC09 format AN files. 
These do not work well with 31DEC08 and will not get correct elevations 
etc.  There is a second problem as well - I believe that the data you 
are looking at was run through our pipeline when it had an error.  That 
error would cause some of the antennas in the AN file to have the wrong 
By sign - actually those antennas will have the correct sign so far as 
31DEC08 is concerned and the ones we think are correct will be wrong for 
you.


You can try fixing the By by hand with GETTAB and PUTTAB.  The following 
stations should have By positive in 31DEC08:

'SC','GB','HN','AR','RO','YS','JB','DEF','KNO','DAR','MK2','TAB'
'BR','FD','KP','LA','NL','OV','PT','Y','MK','GO'

This probably covers all your stations and then some (I tried looking 
for your data bet there are 1000's of files seemingly...)

A better alternative would be to download the FITS-IDI files for your 
experiment.  The uvfits files are currently corrupted until we fix the 
archive.  So in either 31DEC08 or 31DEC09 your only choice is to 
download FITS-IDI and run FITLD from there plus all of the simple fixup 
procs.

Eric Greisen