[daip] negative elevation values: BL149CC

[Yuri Y. Kovalev]

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).

Cheers,
Yuri
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