[mmaimcal] pointing-introduced phase errors scale with surface rms?

[Harvey Liszt]

Darrel--

Take a look at what started this from Bryan Butler,

Gorham, P.W., and D.J. Rochblatt, Effect of Antenna-Pointing Errors on 
   Phase Stability and Interferometric Delay, JPL TDA Progress Report 
   42-132, Feb. 15, 1998.

which is in the back issues available at

http://tmo.jpl.nasa.gov/progress_report/

The 1st issue in front of us now is whether the phase errors measured on the 
DSN antennas scale with wavelength and diameter (only), in which case an
0.7" pointing rms might affect short wavelength observing for the mma, for
the reasons discussed there.

I agree that extended sources have phase structure which point sources don't 
have.  Isn't how we map them?  But do pointing errors then distort extended 
sources (which you seem to be arguing).

regards, Harvey

ps

isn't this why, for instance, we want the axes to intersect to high accuracy?
we hope that this sort of error is either negligible or repeatable so it 
can be removed.
 
>     There's another subtle effect that's probably of no consequence.  The
> phase center of the dish won't in general correspond exactly to its axis
> of rotation.  So, even looking at a point source, this will introduce a
> phase change as a function of antenna pointing, just because of the
> geometry of the motion of the antenna phase center.  My guess is this is
> quite negligible in our context.
>