[evlatests] OTF Holography Tests

[Bryan Butler]

Almost certainly easiest to get it from the Pointing table in the SDM.

	-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