[evlatests] OTF Holography Tests

[Ken Sowinski]

On Thu, 10 Feb 2022, Bryan Butler via evlatests wrote:
>
> Almost certainly easiest to get it from the Pointing table in the SDM.

I have been trying to convince myself that the Pointing table
contains all the necessary information to implement Barry's second
suggestion, but have not yet succeeded.

Ken


> 	-Bryan
>
>
> Barry Clark via evlatests wrote on 2/10/22 16:29:
>>  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.
>>> 
>>>
>>>  _______________________________________________
>>>  evlatests mailing list
>>>  evlatests at listmgr.nrao.edu
>>>  https://listmgr.nrao.edu/mailman/listinfo/evlatests
>>
>>  _______________________________________________
>>  evlatests mailing list
>>  evlatests at listmgr.nrao.edu
>>  https://listmgr.nrao.edu/mailman/listinfo/evlatests
>
>
> _______________________________________________
> evlatests mailing list
> evlatests at listmgr.nrao.edu
> https://listmgr.nrao.edu/mailman/listinfo/evlatests
>
>