[mmaimcal] Meeting

[Mark Holdaway]

Leonia,

This "noise" that is in question is due to opacity fluctuations in the
atmosphere, due in turn to nonhomogeneously distributed water vapor.  The
emission from these fluctuations is not correlated on interferometric
baselines, but seriously limits total power observations.  It is not
a standard sort of noise in anyone's noise equations, but you can
convert these brightness fluctuations (or residual brightness
fluctuations if you have a switching scheme) into an equivalent noise
level.
 
Since the opacity as a function of frequency for a given amount of water
vapor is sort of a smooth function (it certainly isn't random) the
atmospheric brightness fluctuations will be correlated over the sorts of
bandwidths we are talking about (ie, several GHz).

	-mark