[evlatests] OTF Holography Tests

[Barry Clark]

The l,m can be easily calculated from the time and the reference time in 
the script.  Easiest way is probably to do the calculation and store the 
results in the u,v slot.  Problem is knowing what the reference time was 
and where the antenna was commanded to be pointed at the reference 
time.  These can be grepped from the .evla script, but that's pretty 
inelegant.  Alternative is to calculate true az-el of the source for 
each time, and subtract from the antenna position stream - probably 
easier in CASA than AIPS.

On 2/10/2022 3:49 PM, Rick Perley via evlatests wrote:
> A few weeks back, Ken requested some help in testing out a new 'OTF' 
> scanning mode -- to be used for antenna holography.  This initiative 
> was spurred by suggested holography measurements for the ngVLA 
> prototype antenna.
>
> Last week, a short test was done to see if Ken's initial stab at this 
> was in the right direction.  I generated an SB with two orthogonal 
> cuts using our traditional 'stop and stare' method. The test had 31 
> positions, each 10 seconds, done at X-band on 3C84. 5X oversampling 
> was used (i.e., the grid spacing was lambda/5D radians).
>
> To this Ken added two paired orthogonal OTF cuts:  The first pair with 
> a scanning speed set to 'match' the stepped test, the second pair to 
> go twice as fast.
>
> The usual difficulties expected when trying something new were 
> experienced, but with Bill Cotton's help, a data file readable by 
> BDFIn was produced.
>
>  Attached are ten UVPLT files -- no calibration was done.  Single 
> baseline (fixed x moving:  ea28 x ea01) single polarization.  No 
> averaging.
>
> The first two (#1 and #2) show the standard 'stepped' profiles. First 
> in Elevation, second in Azimuth.  (The overshoot on the steps show 
> that ea28 has an old ACU).
>
> The last eight show Ken's OTF cuts.   The first four are each 95 
> seconds long, the last four are half that (twice as fast).  By 
> comparing the heights of the sidelobes, I can tell that:
>
> #3 and #7 plots are in azimuth, reversed direction from #1.
>
> #4 and #8 are in azimuth, same direction as #1.
>
> #5 and #9 are in elevation, reversed direction from #2
>
> #6 and #10 are in elevation, same direction as #2.
>
> The profiles are just gorgeous!  The motion is clearly smooth and 
> continuous.  No sign of problems at beginning or end.  The 
> 'double-speed' profiles look identical to the 'half-speed' ones. 
> Phases look good as well.
>
> That's the good news.
>
> The bad news is that the (l,m) coordinates are rubbish.  All zeros for 
> the first seven 'OTFRASTER' scans, and some enormous numbers for that 
> last scan.
>
> Ken is now thinking about how to get proper (l,m) coordinate 
> information, and in adding various other options.
>
>
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