Experiment setup

• alfa receiver (rotation angle fixed at 0deg)
• Alfa notes:
• beam 3b was turned off .. it was dead
• beam 6b has been bad.. but it think it had recovered (check cal deflection).
  
• jpl horizon ephemeris file was used to track the moon.
  
• one 6.4 MHz band  centered at 1410 MHz
  
• mock spectrometers used in voltage sampling mode
• the 6.4  MHz band was complex sampled  and recorded 16 bits (both pols)
  
• a +10MHz analog offset followed by a -10 MHz digital offset was used to get rid of a/d DC and analog 60 Hz.
  
• output was done using the pdev file format
• see pdev file format for the  output file format.
  

Observing  notes

14feb16:

• Start file: /share/pdata[1..7]/pdev/s3039.20160214.b[0..6]s1g0.00000.pdev
• there were 232 files for each alfa beam
  
• All times below are approximate.. except the start time is exact
• wait till on moon.
• adjust power levels for 1 sigma = 15 counts
• most were higher since all gain was removed and still about 15 counts.
  
• 16:49:54  (ast) start taking data (exact)
  
• 16:51:31  high cal turned on (manually)
• 16:5200   high cal off (manually)
• 19:16:00   high cal on .. still on moon
  
• 19:16:30   high cal off
• xxxx          off the moon
  
• 19:29:30    high cal on  (off the moon) (rms probably now has too few counts)
  
• 19:30:30    high cal off
  
• 19:30:xx    done with observation
  

15feb16

• start file: /share/pdata[1..7]/pdev/s3039.20160215.b[0..6].s1g0.000000.pdev
• had 3 separate scans
  
• 000 .. 021
• 100 ..172
• 200 .. 342
• Total of 238 files/beam
• Waited till on moon.
• adjust mock power levels. 1 sigma=15 counts
• 17:40:55  started scan file .00000.
• 17:32:00   high cal on for 30 secs
• 17:32:30   high cal off
  
• 17:05:00  cal on 10 seconds
• 17:56:41  started scan file 00100
• 18:48:34  start scan file 00200
• 20:22:00   high cal on for 30 secs (still on moon)
• 20:22:30    high cal off
  
• 20:27:00   high on for 30 secs (off the moon) rms counts probably now too low
• 20:27:30    high cal off
  
• 20:27:xx   done with observation
  

Quick look at the spectra: 

Pointing error.

What happened:     

  For the 14,15feb16 run there was an operator (me) generated pointing error. Here is what happened.

• We use an ephemeris file from jpl horizons to track the moon.
• the ephemeris file can be downloaded in J2000 or Apparent ra,dec coordinates (more info)
  
• the download was done requesting apparent ra,dec
• When telling  the pointing program to track the ephemeris, the user needs to specify the coordinate system of the ephemeris
• pnt tr 1 2 -cE   E --> J2000
• pnt tr 1 2 -cR   R --> ra dec apparent, receive ephemeris
• My mistake was to tell the pointing program that the ephemeris file was J2000 (when it was actually ra,dec apparent).
• this means that the precession, nutation, and aberration were done twice.

Computing the pointing error:

    To compute the pointing error:

• In the following let
•  _C  be the correct coordinates that we should have used
• _U be the coordinates we used. these are in error because of the j2000,apparent mixup
• Take the ra,dec from the ephm file and compute az_U,za_U  assuming the ra,dec was J2000 (this is what the pointing program did).
• compute the great circle error az,za . this is the beam 0 error.
• srcAz_Correct  - srcAz_Used ... za_correct - za_Used.
  
• Note: the ephemeris reports source, not feed az .. so the a error is source az error.
• Compute the ra,dec alfa bm offsets from the center of the moon.
• Assume that the moon center is bm0 of the correct ephemeris position.
• given the az_C,za_C for bm 0, back compute the ra,dec for each alpha beam.
• These are the ra,dec  positions the beams would have pointed at  if we had tracked the center of the moon.
  
• given the az_U,za_U for bm  0, back compute the ra_U,dec_U  for all beams.
• To compute the ra,dec offsets:
• convert raHours to deg
• ensure the bm0 doesn't get wiped out while subtracting..
  
• ra_offset_Cor[*,ibm]= (ra_cor[*,ibm] - ra_Cor[*,ibm0] )   * cosDec...
  
• ra_offset_Used[*,ibm]=(ra_Used[*,ibm - ra_Cor[*,ibm0]) * cosDec
• dec_offset_Cor[*,ibm]=(dec_cor[*,ibm] - dec_Cor[*,ibm0])
• dec_offset_Used[*,ibm]=dec_Used[*,ibm]-dec_Cor[*,ibm0]
• The total ra,dec errors is just the 2 offsets added in quadrature.

The plots show the pointing error (.ps) (.pdf):

• Page 1 bm0 pointing error. Zero would be pointing at the  center of the moon.
  
• top: az,za error (correct - used).
  
• * is za, + is sourceAz. black is 14feb16, red is 15feb16
• bottom: total great circle error.
• Page 2-3 14feb16
• 2- ra,dec offset for correct tracking
• top: raBm - raBm0_correct vs az  (great circle)
  
• middle: decBm - decBm0_correct vs az
• bottom: sqrt (raOff^2 + decOff^2
• 3- ra,dec offsets for the ra,dec used
• The reference is bm0 for the correct pointing
• Page 4-5. 15feb16 ra,dec offsets ..

processing: x101/170301/veena_moon.pro

 home_~phil