[daip] forwarded message from Greg Ball

[Eric Greisen]

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From: Greg Ball <gball at cfa.harvard.edu>
To: egreisen at nrao.edu
Subject: Atmospheric opacity solutions with APCAL
Date: Wed, 9 Mar 2005 16:05:59 -0500 (EST)

Hi Eric,

I'm trying to assess the quality of opacity fits by APCAL.  I have Tsys 
values down to very low elevations (about 2 degrees) and fits for several 
of the antennas don't agree well with these points; the asymptotic Tsys 
values for low elevation differ between the data and model.  I'm wondering 
whether this makes the zenith opacity determination suspect or not.

On the one hand, the plane parallel atmosphere approximation will break 
down where sec(z) is high, so I don't expect exact agreement.  But on the 
other hand, my guess would be that at low elevation Tsys tends to a limit 
of Trecvr + Tatm, and the model should reflect this;  therefore the 
discrepancy might indicate a badly fit Trecvr or something wrong with the
weather data...

any hints?

Thanks,

Greg Ball

- --
Gregory H. Ball             Harvard-Smithsonian Center for Astrophysics
Graduate Student            60 Garden St MS #10, Cambridge MA 02138, USA
Astronomy Department        Email: gball at cfa.harvard.edu
Harvard University          Office: +1 617 496-4946
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