Model 19 was installed 30nov17 17:00

Links to plots:

Links to sections:

Introduction/ sequence of events (top)

• Hurricane maria hit AO on 20sep17 with high winds and > 34 inches of water (in 1 day).
  
• The linefeed fell into the dish, damaging panels and changing the weight distribution on the azimuth arm.
• on 27oct17 1.4 kips was added to the lead ballast at the end of the azimuth arm to compensate for the missing linefeed.
• calibration scans done immediately after maria (without tiedown control) showed problems with the pointing.
• The last model update was feb 2012 after the platform beam repair,  so a new model was overdue.
• 22oct17:
• The platform tilt was checked  using the tilt sensors and azimuth swings.
• 22-31oct17:
  
• Calibration data was taken, but not used since the tiedown tracking was not yet working
• 01-18Nov17
• Calibration data used to make the model was taken
• 19,21Novnov17
•  sbn tracked 6 sources with the new model (model19) installed.
• 22,25Nov17
•  the other receivers (327,430,lbw,sbw,sbh,cb,xb,alfa) tracked 1 or more of the 7 sources using model19.
• This was used to measure the constant offset between sbn and the other receivers.
• 01dec17 installed model
  
• 04,05,06,07 added B1005+077. tracked with sbn, 430,cb,xb,sbh
• 09dec17 - updated 430,cb,xb to offsets to include 04-07 source
• but they where added incorrectly. 4-7dec was taken with model19, not the model19verify.
  
• these had different offsets.. mainly affected 430.
• 11dec17:  added 05-07 offsets correctly and updated models.
  
• Note.. some of the text does not include the sources 04-07dec17..never got around to updating it.
  

Taking the input data for the model:(top)

• Before taking the data for the model, the platform tilt was checked:
• Azimuth swings using the tilt sensors were done on 22oct17 to check that the relative tiedown offsets were correct.
• If one or more tiedown cable lengths changed, then a tilt sensor azimuth swing would have a residual 1 azimuth term.
• The measured 1 azimuth term amplitude was <= .0021 degrees. This is a small value.
  
• The tiedown reference positions were left  unchanged.
  
• The data for  model19 data was taken with model18A installed.
  

• Each day the pattern  data points were examined (see daily plots)
  
• A pattern was excluded if any of the tiedowns lost tension during the pattern.
• There was a problem with this test 01-14Novnov17:
• tiedown 8 had 1 working load cell, and it had an offset of -8 kips.
  
• When the loadcell read 0kips, there was still 8 kips on the cable.
• Instead of throwing out all td8 points with 0 tension, i kept those points when the tension 1st read 0. I also looked at the pointing errors throwing out any that showed large offsets.
• This may have included some points with no tension.
• We ended up with 435 usable spider scan patterns.

Daily checks of the data quality. (top)

    Bad data could be caused by no tension in a tiedown , or the platform out of position. For each day, plots were made to find any points that needed to be excluded(not tiedown tension, or platform way out of position).

These plots included:

• Page 1: az,za errors for entire night
  
• top: za error vs pattern number (there is a separate pattern number for each frequency band of a cross).
  
•  each source is plotted with a different color/symbol
• red + are plotted where the td tension was less than 1 kip.
• The vertical dashed lines show the patterns that were excluded
• 2nd frame: az error vs pattern number
• 3rd frame: tiedown tension vs patten number. black: td12, red: td4, green: td8.
• The purple * occur where one of the td tensions was less than 1 kip. The dashed vertical lines were the patterns actually excluded.
• bottom: platform vertical offset (in cm) from the nominal position.
• dropouts are where the distomats failed to read
• Page 2-N. az,za errors vs za are plotted for each source.
• + (black) are the za errors, * (blue) are the az errors.
• The red + are the points that were excluded.
  

The data used to compute model 19. (top)

• Fig. 1 is the azimuth/zenith angle coverage.
• most models have strips spaced every 2 degrees in dec. We did not have complete coverage for model19.
  

• Fig. 2 az,za errors vs azimuth
  
• This is relative to model 18.
  
• The left half of each plot is the northern portion of the dish (southern sources with declination < 18.2 degrees).
  
• The right half of each plot is the southern portion of the dish (northern sources).
• You can see a large offset in the za error vs azimuth. Most likely a 1 azimuth term.
  

• Figure 3 az,za errors vs za.
• A linear ramp in za error vs za was fit to the data : zaErr(za)= 7.2 + .063*za [asecs](-1.6 + .28*za).
• This change could be from a change in the weight of the dome... but my guess is it is a 1 az term (see later plots)
  

• Figure 4 az,za errors by source
  
•  The sources are color coded.
• This is used to check for source position offsets.

• Fig. 5 arrow plot of total errors versus azimuth and za.
• The length of the arrow is the magnitude of the pointing error.
• The angle of the arrow is the direction (radial errors are za only errors)
  
•  1 tick mark on the plot  is 5 arc seconds.
•  At the bottom is a table of the average magnitude and rms for the entire dish and computed for every 5 degrees in za.
• the northwest quadrant (upper left) is the only one with smaller errors.
  

• Fig. 6 has the raw az, za errors plotted versus azimuth.
  
• The model 18 correction has been removed. Model 19 will be fit to this data set.
•  Fits to 1az, 2az, and 3az have been over plotted with the amplitude and phase angle of the maximum.
• The table below compares the values measured for model18 (feb12) and model19 (Nov17).
• 
  

• model		1az		2az		3az
  		amp asec	phase deg	amp asec	phase deg	amp asec	phase deg
  model18	zaerr	97.4	180.8	9.9	175.3	13.4	67.2
  	azerr	91.1	92.0	6.5	60.1	15.9	67.7
  model19	zaerr	107.4	175.2	4.3	180.3	8.2	124.1
  	azerr	88	76	24.7	50.5	47.4	65.4

  
  
• Notes on the values:
• with the model removed, these values should be measuring the underlying errors in the telescope (either structural or tiedown imbalance).
  
• the azimuth arm is suspended on the ring girder by the azimuth trolleys.
•  the wheels are spaced up to +/- 30 degrees from the central azimuth direction.
• so tilts in az or za are spread over an area of about 60 degrees.
  
• 1az:
  
• model 18. the az,za term have similar amplitudes and they differ by 90 degrees.
• model 19. The 1 az  amplitude for za increased by  10 asecs. The az amplitude decreased.
• The tiedown offset positions were not modified between model 18 and 19 (of  course the tiedown encoder position could have changed by a small amount).
• a tiedown change of 1.7 inches (1 inch at platform) would give a pointing error of about 12 asecs,
  
• 2az:
• model 18: the amplitude is small. 6-9 asecs
  
• model 19: the az error amplitude is 25 asecs
• there isn't an obvious 2az symmetry in the telescope  to cause this error,.
  
• 3az:
• model 18: about 14 asecs with phase angle of 67 degrees for both az and za.
• model 19: the azerr amplitude increased to 47.4 asecs
  

• Fig. 7 shows  the same raw errors plotted versus za.

Fitting the model.   (top)

• I excluded points below 2deg za (they had very large errors)
• I also excluded 4 bad points (error in az or za > 35 asecs)
  

• The encoder table is spaced every .5 degrees in za
• At each point a separate value is computed for the azimuth and za residual error.
• The encoder table is then removed from the model residuals.
• The final residuals are great circle errors.
• To point the telescope to the source, the model correction/encoder table is added to the computed position. .

• Fig. 1:the error residuals versus za for the azimuth and za errors.
  
• Raw errors - model is plotted (the encoder table has not been included).
  
• The computed encoder table is over plotted in red.

• Fig. 2: the error residuals (with encoder table) vs za for the az and za errors.
• raw Errors - ( model + encoderTable) ) is plotted

• Fig. 3: the error residuals (with encoder table) plotted vs azimuth.
•  There is more scatter in the azimuth residuals than the za. This could come from:
  
• The tilt sensor measurements showed a 6az term over part of the  dish.
•  The encoder rack gear for the azimuth also has some runout. This will cause  azimuth scatter (with a za dependence since these are great circle errors).

• Fig. 4: the error residuals (with encoder table) by source.
• B2337+227 (light blue) has larger az residuals.
  

• Fig. 5: the error residuals (with encoder table) by source declination:

• Fig. 6: arrow plot of residuals (with encoder table) vs az,za.
• The length of the arrow is the magnitude of the residual error ( 1 tick mark is 5 arc seconds).
  
• The arrow direction is the direction of the error (radial arrows are purely za errors).
  
• A table of the average error and the errors every 5 degrees za is at the bottom of the plot.
  
• The model parameters and values are printed in the lower right.

Checking the validity of the model.   (top)

• The raw errors for the source are removed (leaving 32 sources)
• The model is recomputed using the 32 sources.
• This is repeated for each of the 33 sources.
  

Fig 1 has the model residuals removing one source at a time.

 0 is the model without B2128+048, 1 is the model without B2338+132.. to 25=J1042+120

The black line is the total rms residuals while the red is the azimuth and the green is the zenith angle.

The top plot does not include the encoder table while the bottom plot includes it. 

Removing the 2nd  (count from 0) source B0116+082 makes the largest improvement in the model. Looking at  figure 6  from the previous section it looks like the last 6 points before setting for this source had large errors.

Figure 2 plots the mean pointing error and its rms for each source track that was not included in the model.

 The model was evaluated without source i

then the mean and rms of the pointing model along the az,za track for source i was computed.

processing:x101/model/oct17/chkmodel.pro

Azimuth encoder table.   (top)

• Fig 1 top is the azimuth encoder table made by smoothing to 1 through 6 degrees azimuth (bottom to top)
• Fig 1 bottom plots the azimuth encoder residuals (black line) for azimuth smoothing 1 through 19 degrees. The green line is the azimuth residuals without the azimuth encoder table. The red line is the total residuals (za plus az) for  the various smoothing.
• Using an azimuth encoder table smoothed to 10deg za  would decease the az error from 4.8asecs to 3.9 asecs.
  
• Fig 2 over plots the azimuth residuals and the az enctable smoothed to 3 and 6 degrees azimuth.
• Fig3 is a Fourier transform of the azimuth encoder table (built with 1 degree smoothing). The top plot is plotted versus cycles and the bottom plot versus period (in degrees). The power is at 4 ,8, and 12 cycles (90,45,and 30 degree spacing). 2,3, and 6 cycle terms were removed by the model. (I think the az encoder rack gear has  15 degree sections...see az rack gear)

The azimuth encoder table has not been included in the final output model ...

processing: x101/model/oct17/mkazenctbl.pro, pltazenctbl.pro

Measuring the constant offsets between sbn and other receivers.   (top)

    The model includes constant terms (great circle) in azimuth and zenith angle for each receiver. These terms can differ receiver to receiver because of positioning error of the horn on the rotary floor. The model is made with sband narrow. After the model we need to compute what the constant offsets for the other receivers are (ideally it would remain constant between models if nothing is moved).

• On 19,21Nov17 6 sources were tracked using the sbn receiver  and  model19 installed
• On 22,25Nov17 these same sources were retracked using the other receivers (cbw was not used).
  

The table below shows the sources tracked on each day.

•  The daily plots show:
•  the pointing error all sources, by pattern number
  
• tiedown tensions
• and platform height (to decide if the points should be used for the verify).
• plots of az,za error by source
  

Data sets used for verify, by date:

     The tracking error for each receiver is  plotted below:

(1 receiver per page.. 8 pages) with the sbn error for that source over plotted in black.

• When computing the receiver offset, I  excluded all points below za=3 degrees (since the azimuth is moving pretty fast and the pointing error can be large)
• The plots have 1 receiver per page.
  
• On each page the sbn errors for this source are over plotted in black.
  

• pages 1-8

• The red,green, blue, purple colors are different frequencies or bandwidths used for the observation
• the black plot is the error measured by  sbn.
• For each band  the offset is computed (median(sbnErr) - median(RcvrErr)) and then printed.
  
• If 1 source tracked,  then the az error is on the top ,and the za error is on the bottom.
• If multiple sources are tracked for the same receiver then az Errors are on the left and za errors are on the left.]
• Page 1: 327 rcvr, 3 frequency/bw bands
• B1040+123. first 4 az error points have large pnt error slope relative to sbn run
  
• Page 2: 430 rcvr. 3 frequency/bw bands
• B1040+123. only 2 points measured. The az error has same large slope (relative to sbn) that was seen in the 327 measurement using this source.
• The offset measured is unreliable (but the beam width is large... so maybe no too much of a problem).
• Page 3: lbw rcvr. 4 frequency/bw bands
  
• B2325+26.  stable offset measured.
• Page 4: sbw rcvr. 4 frequency/bw bands
• B0758+143.  offset not constant for  part of run. probably good to a few arcsecs.
• Page 5: sbh rcvr.  4 frequency/bw bands
• B0758+143.  offset good to a few asecs.
• Page 6 : cb rcvr.. 4 frequency/bw bands
• Sources: B0134+329,B0316+162,B0518+165
• This did not give repeatable results.
• az error differences: -3 to  +4asecs
• za error differences: -13.5 to -4 asecs.
• Page 7: xb rcvr. 4 frequency/bw bands
• Sources: B0134+329,B0316+162,B0518+165
• This did not give repeatable results. The xb za error went from way above sbn to way below sbn rise to set.
• the xband beam is not very well formed...
• 
  
• Page 8: alfa rcvr. 1 frequency band, beam 0.
• the offset is relatively stable.
• there is a 24 asec offset in za.
  
• page 9
• For each receiver:
• plot the median difference (median(sbnErr) -median(rcvErr)  for each band measured.
• If multiple sources tracked, over plot the errors in red and green.
• + are the az errors
• * are the za errors.
  

Misc: (top)

File locations.

• The new model is model19A
• enctbl19A is the encoder table for model19A
• While the model is being made and verified, the subdirectories in etc/Pnt  used are:
  
• OldModel18 - this holds all of the old model18 models
• NewModel19 - this holds the final version of model19
• VerModel19 - this has the models used to measure the offset between sbn and the other receivers.
• modelSB is the  model19A model
• All the the  other receiver models are the same as modelSB except:
• the offset for each receiver is computed using modelSB and making the offset term difference between sbn and the other receiver the same as model18
• Scripts to install the model:
• The pointing program uses the models in /home/online/vw/etc/Pnt
• There are 3 scripts in etc/Pnt that copy models from a disc location to the active location (vw/etc/Pnt)
• getModelsNew.sc - copies the final model19 to etc/Pnt from NewModel19/
• getModelsOld.sc  - restores model18 to etc/Pnt
• getModelsVerify.sc - copies the models used for the verify run to etc/Pnt
• Running any of these scripts in /home/online/vw/etc/Pnt will execute their function.

Summary: (top)

• model19A was made 01Nov17 through 25Nov17,
• It was  installed as the current model 30nov17 17:00
• 33 sources were tracked yielding 435 points (calibration patterns).
  
• We did not have a complete declination coverage for the sources.
• The sbn pointing error residuals were:

• 	za residuals asecs	az residuals asecs	total residuals asecs
  model 19 noEncTable	6.02	7.23	9.41
  model 19 with EncTable	3.06	4.76	5.65

  
  

• The other receiver constant offset measurement:
• The sbn run on 21Nov17 had trouble with some sources (lost distomats, for awhile) (3C48)
  
• cb,xb used this source for 1 of the 3 sources.
• The sbn pointing errors for these sources was:

• 	mean Asecs	rms Asecs
  zaError	-.93	4.76
  azError	.37	5.92

•  
• So the errors were reasonable (these sources were used in making the model).
  
• The offsets for 327,lbw,sbw,sbh and alfa were measured reliably
• The za offset for alfa changed by 24 asecs.
• The error may have been present in alfa for awhile (we hadn't done an alfa pointing run for over a year).
  
• The 430 offset only had 2 common points with sbn.
  
• The 430 za offset difference  had a large change with za.
  
• The 327 receiver saw this same pattern (since it used the same source).
• It may be that the sbn track of this source rising, had trouble.
  
• cband
• 3 sources were tracked: 3C48,CTA21,3C138
• The za error offsets varied -5 to -13 asecs.
• xband:
• 3 sources were tracked: 3C48,CTA21,3C138
• the az offsets varied -4 to +5 asecs,
• the za offsets varied 2 to 9 asecs.
• the beam was not well defined. the 1st side lobe got up to -10db or worse.
  

 home_~phil