History: (top)

• 19jan15: had left off refraction correction (see main history). corrected 19jan15
  
• 27jan15: 17:00 model 2A installed.
  
• 28jan15: 325 crosses on casA using model2A to check the model.
• feb16-mar16: model3A made
• jul21     : switched to using regular mock cross scans to make model
• sep21    : model 4A
  

The 12meter model:(top)

• Use the model that is hard coded in the controller (defined by mark goddard ..8 parameters)
  
• load the model parameters into the  controller memory
• select the option for the controller to apply the refraction and then model correction
• You supply a value for dut1 to the controller (ut1-utc). The controller then runs its system clock on ut1 (not utc).
  
• You need  be sure and  update dut1 whenever needed.
• This ability is needed if you want to use the controller to track in ra,dec (it does the conversion to az,el and then model correction).
• The only problem here is that the controller does not do precession or nutation, so you must provide ra,dec of Date.
  

• The model is evaluated in the computer. this gives more flexibility in what kind of model we use.
• I'm using mark's model because it seems to work.
  
• We turn off the options for the controller to apply any refraction or model corrections (it is  done outside of the controller).
  
• We can set dut1 to 0. in the controller  (so it is running on UTC)
• So all of the time stamps returned from the controller do not need to be converted from ut1 to utc.
• the model values are added to the az,el computed by the ra,dec to az,el conversions before being sent to the controller.
  
• azenc=AzComputed + (azmodel)*gcToLittleCirle
• The model values are great circle errors...
  
• elenc = ElComputed  + elmodel (including refraction)
  

The model parameters:

    The model parameters were defined by mark goddard. There are 8 parameters in the model.
When converting ra,dec to azEncoder,Elencoder (that is sent to the controller):

• Convert ra,dec to az,el
• convert el -> elRefract   (apply the refraction correction to the elevation)
• evaluate the model use az,elRefract -> azModDelta, elModDelta (these are great circle)
• The values to send to the 12meter are then
• azEncoder= Az + azModDelta/cos(elRefract)   (to go greatcircle  to little circle)
• elEncoder = ElRefract + elModDelta

The AzModDelta,elModDelta are (the results are great circle)

Notes:

• P4 and P5 are common to the azimuth and elevation computation.
• P6 is not used
• azimuth axis tilt (phi) and direction (Ka) can be computed from P4 and P5
  
• azTiltDirection(Ka) = atan(-P4/P5) = atan( -(-phi*sin(Ka))/(phi*cos(KA))*!radeg
• azTiltAngle(phi)       =P5/cos(Ka) = -P4/sin(Ka)
• this should also be a consistency check. 
  

Making the model: (top)

• Taking the data:
• Currently only xband is used to make the model since the rfi from sband is saturating the system.
  
•  Crosses are done while tracking continuum sources.
• A strip in azimuth followed by  a strip in elevation
• spectral data is taken with the mock spectrometers during each strip (1 scan/file per strip).
• The total power is computed throwing out band edges and rfi.
• 7 172Mhz bands spanning 1 Ghz are taken during the datataking and processing.
  
• Computing the offsets:
• For each cross a 2-d gaussian is fit to the data giving beam offsets for pointing errors (as well as bmwidth,amplitude,etc)
• Fitting the model:
• After tracking multiple source across the dish (doing crosses), the  measured offsets are then fit to the beam model giving the 8 model parameters.

Taking the data: The crosses

    A cross consists of a strip in azimuth through the source followed by a strip in elevation through the source. The mock spectrometer takes a scan of data during each strip.  The newer models are using xband.

    The table shows the parameters used for the crosses.

• Mock setup:
  
• 7 mocks used
• Each mock:
• 172Mhz bw, 1024 freq channels, .1 sec sampling, 32 bit spectra
• If/lo setup
• mock 172Mhz bw spaced by 142 Mhz in iflo (for overlap) covering xb Rf: 8135 to 9159MHz (the downstairs IF has a 1 Ghz filter).
• mock cfr:8221.00 8363.00 8505.00 8647.00 8789.00 8931.00 9073.00 MHz
• The udc lo is set to map the center of the mock bands (8647MHz) to the center of the 1-2 GHz IF.
• The udc attn is set to 15,15 db (max)
• the software: basedir:/share/megs/phil/svn/aosoft/p12m/
  
• ./x101/   location to run on galfas2 tcl session
• contains the tcl scripts used for each days observation
• 210909_cross.tcl for 9sep21
  
• setupcross.tcl - generic cross setup
• ./tcl/pnet/cross.proc  - tcl cross procedure
• ./tcl/gen/ifsetup.proc - setup the if/lo
• ./tcl/pnt/pnt    -tcl interface to pointing.
• ./tcl/logfiles/user/.. user log files for a day (may continue into next day if datataking crosses midnight)
• user_20210909.log  .. has ra,dec, scan az,za and time for az,el scans.

 Computing the total power from the spectra

    The crosses are input using the idl routine crossinp.pro. When computing the total power from the spectra:

• Each spectral band is 172Mhz wide. There are 7 bands recorded covering the 1Ghz.
  
• By default 6% of the band is excluded on each side (where the filter changes rapidly)
• the user can input frequency ranges that will be excluded when computing  the total power
• currently 8319 to 8349 Mhz is excluded because of recurrent rfi. (see model/init.pro)
  
• the rms/mean by freq channel is used to further exclude rfi
• Only the azimuth strip is used (since the za strip has a larger change in tsys)
• the first 400 spectra and the last 400 spectra of the strip (1st 1/3 and last  1/3)  are used. the middle 1/3 is excluded so the  source does not affect the rms/channel.
  
• the rms/mean by channel is then computed for the 800 spectra and a linear fit is done to  the rms. Any freq channels with > 3sigma outliers are not included in the total power computation.
• We end up with 1200 total power numbers per pol per freq band per strip (there are 7 freq bands).
  

Fitting the 2d gaussians to the total power crosses.

    A 2d gaussian is fit to each cross to get the measured pointing offset (as well as other info). The total power from the two polarizations is combined prior to the fit.
The gauss fit is:

• There are 8 parameters. It includes a rotation of the gaussian in case the beam is elliptical.
  
• a0 - constant
• a1 : amplitude
• a2 : xoffset ,az coord direction
• a3 : yoffset ,el coord direction
  
• a4 : sigx^2  ,in prime coordinate system
  
• a5 : sigy^2  ,in prime coordinate system
• a6 : theta   ,rotate unprimed to primed system so xp,yp are aligned along ellipsoid of beam
  
• a7 : slope   ,fit for slope of Y (usually el during strip)
  
• z(x,y) = a0 + a1*exp[-xp^2/sigxp^2 - yp^2/sigyp^2]
• xm=(x - a[2])  . .remove x offset
• ym=(y - a[3])  .. remove y offset
• xp=xm*cos(th) + ym*sin(th)
• yp=-xm*sin(th) + ym*cos(th)  .. rotate to align xp,yp with ellipse major,minor axis
• The processing is done in idl
• The 2d fitting routines:
• /share/megs/phil/svn/aosoft/p12m/pro
• gsfit2d_12m.pro

Fitting the model to the pointing offsets:

    The pointing model used for the 305meter had separate parameters for the az and el (there were no shared parameters). That made it easier to fit to the measured az and el errors.

    The 12meter model parameters P4 and P5 are used in the az and the el error computation. I played around a little trying to fit the 2 data sets (azerr,elerr) separately but ended up fitting them both at once:

•  modAz=P1 + p2*cos(elR) + P3*sin(elR) ....
  
•  modEl =-P4*sin(az) + P5*cos(az) .....
  
• fitFunct= (MeasuredAzErrAsec  - modAz)^2 + (MeasuredElErrAsec- modEl)^2
• When calling the curvefit routine the expected value is 0. for all crosses.
• Prior to calling the non linear curvefit routine, i  do a linear fit on the az  and el errors separately (getting two values for p4 and p5). I use the output of these fits as the starting values for the nonlinear fit (averaging the two values for p4 and p5).
  
• the current idl fitting routine is in p12mfitmoda.pro (a is for all params at once).
  

Example session: (top)

Track  3C273  rise to set doing crosses

• connect to vnc session on galfas2
• cd /share/megs/phil/svn/aosoft/p12m/x101/
• If  the tclsh session is not running:
• tclsh
• source startup.tcl    .. to initialize things
• the commands to execute are in 210908_cross.tcl
• you could just source this  file , or copy and paste executing 1 line at a time.
• I'll list the commands here:
• chknewday  .. so log file names use current day.
• set source  3C461  ; will set variables ra,dec
  
• source setupcross.tcl ; inits for cross.
  
• #  spaced by 142 Mhz.
• setfreq -m 8221.00 8363.00 8505.00 8647.00 8789.00 8931.00 9073.00
• #move off to adjust power
• pnt tr 90 75 -cx
• pnt mode tr
• waittrk tmI 1
• # set power levels
  
• attn if2 5 8
• if2mp
• 1 -42.56 -42.44   ;; reply
  
• mockadjpwr 30 reply
• b0s1g0  rms:A  30.5   29.0 B  29.5   30.9 mn:A   0.1    0.5 B   0.4   -0.5 gn:  9  8  
• b1s1g0  rms:A  29.4   27.4 B  26.6   26.4 mn:A   0.1    0.6 B   0.1   -0.1 gn:  4 10  
• b2s1g0  rms:A  29.7   29.7 B  30.4   28.2 mn:A   0.4    0.5 B  -0.2    0.0 gn: 13 11
  
• b3s1g0  rms:A  29.8   29.2 B  25.1   26.1 mn:A  -0.1    0.4 B   0.5    0.7 gn:  6 11  
• b4s1g0  rms:A  32.1   29.8 B  28.8   28.3 mn:A   0.3    2.4 B  -0.5   -1.3 gn: 14 12 
• b5s1g0  rms:A  25.9   25.6 B  26.9   26.7 mn:A   0.2    0.7 B  -0.3    0.1 gn: 18 19 
• b6s1g0  rms:A  31.7   28.0 B  31.1   31.1 mn:A  -0.6   -0.7 B  -0.7    0.6 gn: 17 18 
• set scram(source) $source  .. so srcname ends up in header
  
• pnt tr $ra $dec                     .. track source ra,dec (variables set by srcget)
  
• pnt mode tr                         .. goto tracking mode
  
• waitsecs 20
• pnt dbg gc 0 0
• set toloop 1440                   ,, set times to loop on crosses
  
• cross $ra $dec j $toloop     ,, execute the crosses.. will kick out when source sets.
  
• pnt mode pwroff                 .. turn off the motors.
  

•  monitoring the cross's with a stripchart recording in idl. hitting the space bar will bring up a menu.
  
• 
  
• idl
• @phil
• @masinit
• maxpnt=1200*4   ; max points in window
  
• masmonstripch,bsg='b1s1g0',date=yyyymmdd,maxpnt=maxpnt 
  

Fitting 2d gaussian to each cross and then computing the model.

• Note that each model will use a separate directory in p12m/model
• you can copy the routines from model4A and update them.
  
• cd /share/megs/phil/svn/aosoft/p12m/model/model4A/inpdat/210908_inp.pro
• idl
• .run ../init
  
• .run 210908_inp.pro
• .. this will input all the crosses taken on 210908
• It will remove rfi and the compute total power from each spectra.
  
• A save file will be generated for each source with the total power and location info for each cross.
  
•  (eg inpdat/2109009_3C273.sav)
  

• when you've created all the save files with total power data, you can fit 2d gaussians to all of the crosses.
• in model4A
• .run fit2dall
• this will generate the save file fitI2draw.sav .
  
• .run fit2dfilter
• The routine fit2dfilter   will try and remove bad crosses (rain, etc).
• And then compute the median  values for each cross (there are 7 crosses . one at each of the 7 freq bands).
  
• it will generate the array of structs fitIM[] 
  
• .run plt2dfit
• plots the values, by running it multiple times you can adjust the final clipping limits for which crosses to exclude.
• It generates fitIMclp[]  
  
• .run computemodel
• this computes the model
• plotmodelres,... 
  
• this will plot the model residuals
• printmodfiti,..   this will print out the values for the model
  
• you can enter these values in the model parameter file
• /share/megs/phil/svn/aosoft/p12m/etc/model12m
• --> note that you will need to restart the p12mProg on galfas2 since it loads the model parameters at startup
• Just kill it.. see /etc/rc.local for starting it.
• All of these routines are gathered in model4A/doall.pro

Disc locations: (top)

• base directory: base=/share/megs/phil/svn/aosoft/p12m
• idl routines:
  
• $base/pro/: some p12m idl routines
• /share/megs/phil/svn/idl/p12m  .. generic p12m routines
• making a model
• $base/model/ : all models under this dir.
• $base/model/model4A/  - model processing , general
• $base/model/model4A/inpdat - holds routines to input and compute total power for each day.
• Pointing program source:
  
• $base/Prog/  : hold source code for pointing program: p12mProg.c
• etc routines
• $base/etc/model12m    - holds model parameters

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