[evlatests] C-Band Imaging comparisons: VLA vs. WIDAR

[Bryan Butler]

so is the conclusion from this that aside from the closure corrections 
needed, the WIDAR data is good?

	-bryan


Rick Perley wrote, On 7/7/09 13:59:
>     I've now been able process the C-band parallel data sets taken last 
> July 4/5. 
> 
>     1) As noted before, all WIDAR images are rotated by 180 degrees 
> about the phase center. 
> 
>     2) The calibrator was 2007+404, an excellent unresolved source.  The 
> VLA data, after closure corrections (recall that both VLA and EVLA 
> antennas are included here) provided a decent map with 28000:1 DR.  
> (There's a weak background source, 2 mJy, located 30 arcsec to the NW). 
>        The WIDAR data are expected to provide a slightly better Dynamic 
> Range:  10 antennas with 512 MHz total BW, vs. 15 antennas with 200 MHz 
> total BW, so the sensitivity should be slightly better.  To obtain this, 
> I had to apply closure corrections to the WIDAR data as well -- the 
> corrections are distressingly large:  typically 0.2% for subbands 1 and 
> 2, and up to 2% for subbands 3 and 4.  (These latter two sub-bands were 
> placed outside the old polarizers' range, and four of the antennas in 
> the WIDAR subarray have old polarizers.  The large corrections needed 
> for subbands 3 and 4 should not be viewed with especially concern, as 
> they are likely due to the polarizers.).  The 'final' DR was 40,000:1.  
> The same weak secondary is easily seen -- reflected about the origin. 
> 
>     3) Cygnus A:  The VLA image, after standard self-calibration, 
> provided a nice image with perhaps 1000:1 DR -- about what is expected 
> for this very powerful and heavily resolved object with the old 
> correlator. 
> The WIDAR image provides about the same formal DR, but is notably poorer 
> in its true fidelity.  I attribute this primarily to the poor (u,v) 
> coverage -- we have a lack of intermediate spacings which are needed to 
> better link the long and short spacings.  
> 
>     I'll now move to the very messy 20cm data. 
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