[mmaimcal]FYI: EVLA Memo # 73 WVR results from the VLA

[Al Wootten]

EVLA Memo # 73

RESULTS OF WATER VAPOUR RADIOMETRY TESTS AT THE VLA

C. J. Chandler, W. F. Brisken, B. J. Butler, R. H. Hayward,
and B. E. Willoughby

NRAO, Socorro

August 9, 2004

We report on the results of one year of tests of a three-channel water 
vapour radiometer (WVR) on two VLA antennas.  The output from one of the 
circularly-polarized feeds of a standard VLA 22-GHz receiver is split on 
exiting the dewar; one signal path leads to a temperature-stabilized 
plate on which the WVR detection system is mounted, the other leads to 
the normal astronomical system electronics.  We measure the correlation 
between fluctuations in astronomical phase (assumed to be dominated by 
the troposphere), phi,  and the WVR difference output from the two 
antennas, on various timescales.  We find that in all cases applying a 
correction derived from the WVR improves the rms phase, for observing 
frequencies ranging  from 8 GHz to 43 GHz.  The improvement is most 
dramatic when the sky  is clear and the tropospheric phase fluctuations 
are large.  When there are clouds present the WVR output is contaminated 
by the fluctuations in system temperature caused by liquid water, and 
the correlation between phi and the WVR output is not as good.  However, 
even in this case the RMS phase is still improved by applying a 
correction derived from the correlation.

View a pdf or ps version of EVLA Memo #73 at:

http://www.aoc.nrao.edu/evla/memolist.shtml