[mmaimcal]TP detectors as atmospheric monitors, continuum band mismatch

[Al Wootten]

Folks,

Several items came up in discussion today which I thought I would report 
back for discussion/comment.

Webber noted that bandpass shape/extent may differ between correlator 
with tunable filter and TP devices--hence the TP device may find itself 
contaminated with a line not seen in the correlator.  This would pose a 
problem in image reconstruction using TP and interferometer data.  The 
tunable filter sections overlap to avoid aliasing; this cuts their 
nominal bandpass below what they would have in the baseline correlator. 
  The do have a bypass more.  Use bypass? We may want to define 
'standard continuum band' without strong spectral lines.  This has been 
discussed before.

Baudry asked if we had considered using the output of the total power 
detectors as a continuum channel which we could compare or complement 
the WVR data on line variations with.  In a discussion, we noted that 
the WVRs (effect seen at OVRO, VLA, IRAM) seem to have a variable 
scaling factor over time which might be traced to 'dry component' 
variations.  Lucas noted that this had been noted at IRAM, though the 
continuum channel did not show this.  Baudry noted that we might wish to 
use the 8GHz TP detector channels for this sort of monitoring.  I think 
this is possible but I'm not sure about the sensitivity of those 
devices.  Earlier in the week, we had decided that owing to 1/f noise it 
was probable that only the 2 GHz channels would be useful for TP 
continuum owing to their lessened susceptibility to 1/f noise.

Discussion or comments?

Al