MEM-VIS and Visibilities
The main difference between MEM-Sato and MEM-VIS is that the former uses
countrate profiles and the latter uses visibilities.
What are visibilities?
- The visibility of a point source:
- The function analogous to the modulation profile is the sequence of
terms Vj on a circle in the (u,v) plane:
- The V values have both amplitude and phase
Visibilities offer certain advantages over countrate profiles:
- Visibilities are hardware independent
- And they are in inertial coordinates.
- Visibility profiles can be added together (count profiles can't).
- The tools of radio astronomy are available for use with visibilities.
Disadvantages
- One disadvantage of visibilities is that they have to be computed from
the countrate profiles.
- but this is relatively straightforward,
- and the computation time is very small compared to the imaging time.
- Another disavantage is that they involve complex arithmetic,
- but astronomers are usually used to this
- and the software does all the dirty work
RETURN
Ed Schmahl
Last modified: Thu Apr 11 09:37:03 EDT 2002