Intro

    On 12aug22 azimuth swings at low elevation were done to determine the horizon mask for  geodetic vlbi observations. We found that some bushes/trees were increasing Tsys at low elevation. Maintenance cut down the trees/bushes that were causing this. On 30aug22 the az swings at low elevation were repeated to see the improvement of Tsys at low elevation.
Some rfi info from the azimuth swings can be found (here).

---

Setup:

• The 12meter was set to xband.
• the setupwcalmap routines was used:
• Standard ifsetup xb
• cfr set to 8646  MHz.
• hardware winking cal used (25 Hz).
  
• 7 mock spectrometer were used:
  
• 172.032 MHz bw polA,B recorded
• cfr: 8219 8363 8505 8647 8789 8931 9073
• 142 MHz spacing
• 512 freq channels
• 2millisecond spectral sampling using 16 bit spectra

• The telescope pattern was:
• az swing at 1 deg/sec between -100 and 282 (and then reversing)
• swings were done at
  
• el=6deg CW
• el=10deg CCW
• el=15deg CW
• data taking started at 07:48
  
• each swing took 380 seconds
• we finished at 08:07
• During the observation the sun location was:
• 88 deg az +/-.75 deg
• elevation at start of swing:
• 6 deg swing: sun at 21.5  el
  
• 15 deg swing: sun at 23.75 el
• The tcl command file user/p12m/x101/220830_azswing.tcl was used to take the data.
  

---

Processing the data"

• Each azswing was read in with  the idl routine masazswinginp() with the hwc keyword set
• masgethwcal()  was used to  input the file
• input file
• separate out calon,caloff cycles
• average 16ms of each calon, off cycle spectra
  
• compute rms/mean for calOn ,calOff spectra
• linear fit to rms/mean.  flag outliers freq channels as rfi
• compute caldeflection (at 40ms intervals)
• do a 3rd order fit and use to correct total power for  electronic gain variations
• compute total  power (excluding rfi and correcting for electronic gain variation) at 40ms intervals.
  
• use the caloff total  power vs  azimuth for the analysis below.
• interpolate the 1 second azimuth positions the to 40ms total power samples
• select the data between -90 and 270 degrees azimuth
• We end up with 9000 (360/.04) samples  times 7 frequency bands (covering  total of 1 ghz)
  

---

Looking at the data:

    The first set of plots show the Tsys vs azimuth for the 3 azimuth swings for each frequency band (.ps) (.pdf)

• Each page is a separate 172 MHz frequency band.
• the 8788 and 8930 MHz band had strong 4sec periodic rfi. (more info)
  
• the colors correspond to the elevations of each azimuth swing
• 30aug20 after trees/brush cut
• black: elevation  = 6deg
• red: elevation = 10 deg
• green: elevation = 15 deg
• 12aug20  before the trees/bushes were cut
• blue: elevation =6deg
• lightBlue: elevation = 10deg
• yellow: elevation =15 deg
  
• The top Frame is polA, the bottom frame is polB
• The vertical axis is in deg K
• The purple vertical line is the azimuth of the sun during the observation
• there is no appreciable bump around the sun azimuth
  
• The sun was at an elevation of 21-24 deg during the test.
• Looking at elevation = 6deg
• blue: the wide bumps are from the trees/bushes (the narrow spike at 204az is tower12)
• black:the wide bumps are now gone. So the clearing of brush/trees was successful.
• There is a new narrow bump at az=19.4 deg in the 30aug22 data .
  
• It is there in all freq bands
• i  checked the ra,dec and there are no strong xband sources at this location.
• Need to check this out.
  
• The increase in Tsys when going from el = 15 deg to el=6deg is from the atmosphere (more info).

The 2nd plot is a blowup around the 12aug22 azimuth bumps (.ps) (.pdf)

• Page 1: the bumps are not present in the 30aug22 data
• Page 2: this is a blowup of the new az=19.4 deg bump seen 30aug22. It is much narrower than the brush/tree bumps seen 12aug22.
  
• It almost looks like a back lobe of tower 12.
•  204.4-180=14.4 deg.
• The structure at the top mimics that of tower 12.
• The widths are about the same.
  
• But it wasn't there in the 12aug22 data.
  

---

SUMMARY:

• 3 azimuth swings were done at elevations of 6,10, and 15 degrees
• The increases in Tsys seen at az=-53 +/-30deg and az=105 +/- 30deg are no longer present after the bushes were cut.
• The increase in Tsys at az=204 is still there (since T12 hasn't moved:)
• A new bump at el=6 az=19.4 was seen with a width of about 3 degs.
• 3 directions showed increase of Tsys when the elevation was 6 degrees

processing: x101/220830/horazswing.pro