system performance after hurricane maria
Plots of gain before,after maria
before after maria
Hurricane maria hit the observatory on
Recovery from the storm included:
- winds over 100mph
- rainfall of 39+ inches in 3 days.
- The linefeed broke off and fell into the dish
- multiple sections of the catwalk floor broke off and fell into
- A lake beneath the reflector (up to 8 feet deep) was
finally drained sometime in November.
- Up to 80 panels needed to be replaced
- 2 east/west cables were broken and had to be replaced.
- the cables were approximately 150 north of ao9 and 100 feet
east of north (these are ballpark numbers).
- 22oct17: platform tilt was checked with azimuth and the tilt
sensors in the dome.
- 27oct17:1400 lbw of ballast added to end of azimuth (ch side)
to compensate for loss of linefeed,
- 01nov17: tiedown tracking becomes functional
- 01-18nov17: data taken (with sbn) for a new pointing model.
- 09dec17: commercial power returns to AO.
- feb18: damaged panels and east-west cables repaired
Degradation of the telescope gain:
The telescope gain will be affected by:
- the accuracy of the reflector surfaces
- the position of the horn relative to the focal point of the
- the pointing error.
- this will normally not be a problem during calibration scans
since strips +/- 3 beam widths in length are used
for the beam fits.
- Normal tracking by observes will be affected by the pointing
Looking at the telescope gain before and after maria.
x102 calibration from Pre and post maria were
used to check the telescope gain. The calibration patterns do 4
strips through the source, each 6 beamwidths long.
- Pre maria: 01jan16 to 18sep17.
- postMaria: 01Nov17 thru 27jan18.
- frequencies/rcvrs used:
- sbn: 2380 MHz
- sbh: 3500 MHz
- cband: 5000 MHz
- xband: 9000 MHz
The table below has the telescope gain before/ after
maria by frequency:
Each file contains two pages:
- Page 1: Gain vs azimuth angle
- Each source is plotted with a different color/symbol
- Top frame: feed in the north half of dish (looking at
- Bottom frame: feed in the southern part of the dish (looking
at northern sources)
- For each frame the data is plotted rise to set.
- the left 1/2 of the plot is source rising (looking at the
west 1/2 of the dish)
- the right 1/2 of the plot is source setting (looking at
the east 1/2 of the dish)
- Page 2: Gain vs azimuth and za as an arrow plot:
- This is an arrow plot that tries to show the gain variation
vs azimuth and za
- The length of each arrow is proportional to the gain
- The top of each plot shows the K/Jy for a tick interval.
- It is not easy to compare different vector lengths (that
change by a small amount).
- The angle of the vector with the top of the page is also
proportional to the gain.
- The top of each page lists the gain for 0deg, 90 deg, and
180 deg rotations
- the range of gain for each plot varies.
- When looking for variations in gain, the eye can follow
vector rotations better than changes in length.
the gain before/after maria:
Gain vs az for common
sources tracked before and after maria (.ps) (.pdf)
- black * are sources tracked before maria
- red * are the same source tracked after maria.
- Comparing the same source before and after removes any error
in the flux measurement.
- pages 1-3 show sband 2380 MHz measurements
- 20 to 30% lower after maria
- pages 4-5 cband, 5000 MHz measurements
- about 50% lower after maria
- page 6 xband 9000 MHz measurements.
- 50 to 75% lower after maria.
Decrease in gain rise to set
- The plots show that the gain is generally decreasing rise to
- Sources that track the southern part of the dish have a larger
- This was visible before and after maria.
- This could be caused by the distance between the horn and dish
- the SE fill area has had sinking problems in the past
(the main cables had to be re-tensioned).
- It could also be a problem with the positioning of the
platform relative to the dish
- the 1az term was measured to be small , so there is
probably not a large tilt.
- The telescope gain has changed before/after maria. Typical
- 2380 MHz 20-30%
- 5000 MHz 50%
- 9000 MHz 50 - 75%
- gains are decreasing rise to set, especially sources that
track the southern part of the dish
- This was evident even before maria.
- the SE fill area of the dish has had problems in the past
- find out if the focal distance is too short or too long.
- track B1328+307 and/or B0134+329 rise to set
at cband or xband using the calibration scans.
- after each calibration scan, move the platform height.
Cycle above, on , and below the expected focal height
- As a function of azimuth see how the gain changes.
- This requires functioning distomats (which we don't have).
- It also needs to be done at night, so there is sufficient
tension in the tiedowns.
processing: x101/171212/ see Readme file.