Theodolite survey of dome from ao9 monument (origin=Reflector)


     The dome position was surveyed from the ao9 monument on 9aug01 starting at about 10pm. This shows the data moving the origin to the center of the reflector (1.34 in east of AO9, .69 in south). See theodolite survey (AO9 origin) for the results relative to AO9. The dome was moved through the following positions:
  1. a za strip from 2 to 19.6 degrees in 1 degree za steps at an azimuth of 242.87 degrees (pointing at tower 8).
  2. a za strip from 19.6 to 1.09 degree in 1 degree za steps at an azimuth of 302.87 degrees.
  3. an azimuth swing from an azimuth of 242.87 to 602.87 degrees in 30 degree steps. The dome was at 19.6 degrees za.
  4. an azimuth swing from an azimuth of 602.87 to 242.87 degrees in 60 degree steps with the dome at 10 degrees za.
Differences between the encoder and reflector  az and za positions-->platform offset from reflector center.
The pitch, roll, and focus errors versus az and za.
Fitting the pitch, roll, and focus.

 Differences between the encoder and reflector  az and za positions-->platform offset from reflector.  (top..)

    The dome and azimuth were positioned using the az, za encoders with no model corrections included. The theodolite vertical is determined by gravity while the theodolite azimuth is arbitrary. To calibrate the theodolite azimuth I used:
TheodAzCorrection= mean(EncoderAz-theodoliteAz)
The average was done over the two azimuth swings and then the correction was  added to the theodolite azimuth encoder values. The theodolite positions were then translated to the center of the reflector (offset .69 in south, 1.34 in east of AO9). The offset was measured using the photogrametry data and a survey of some of the optical targets.  The position differences (reflector - encoder) are shown in the plots:    The azimuth rotates about the main bearing. The bearing is offset relative to AO9 where the theodolite was positioned. AO9 is then offset from the center of the reflector. The combined  offsets create a 1 azimuth term in the differences of the measured azimuth positions (reflector - encoder). The difference was computed as ReflectorZa-encoderZa (and similar for az values). The peak of the sine wave  has the Reflector angle greater than the encoder angle. For this to occur the distance from the center of the reflector to the dome must be greater than the distance from the main bearing to the dome. So the platform is displaced along the direction of the peak. To compute the horizontal distance I generated a circle and then offset by .01 inch steps from 0 to 5 inches. I then computed the differences in the two circles. The offset distance corresponding to 123 arc seconds was 3.09 inches. Projecting this along the phase direction of 339 degrees gives the offsets of the platform relative to the reflector:
radial offset of platform dx offset (east positive) dy offset (north positive)
3.09 inches  -1.11 inches  2.88 inches
    The platform offset relative to the reflector will create a pointing error. The raw pointing errors that were used to build model13 (jan02) do not agree with the measured translation:
pointing error amplitude,phase offset error ampltidue,phase
za:  98 asecs, 185 degrees za: 122 asecs, 339 degrees
az: 98 asecs,  94 degrees az: 122 asecs, 249 degrees
The pointing error is the direction you must move the telescope to correct for the pointing offset. It is 180 degrees from the actual motion. The pointing errors agree a lot better with the offset of the platform relative to just AO9.
processing: survey/010809/reducR/

The pitch, roll, and focus errors versus az and za.  (top..)

    The directions of the pitch, roll, and focus errors are defined as:
  • positive pitch error: the uphill portion of the dome is to high (far from the dish).
  • positive roll error: looking uphill, the right side of the dome is too low (close to the dish)
  • positive focus error:  the dome is too far away from the reflector.

  • The plots show the pitch, roll, focus errors:
    1. Figure 1 top is the pitch, roll, focus errors versus za. Black is pitch, red is roll, and green is focus. The vertical access is degrees for pitch and roll, and inches/10 for focus (.1 == 1 inch). The zastrips and azimuth spins are plotted with different symbols. The  measured radius of curvature for the reflector was used (869.781 feet).
    2. Figure 1 bottom is the same errors plotted versus azimuth angle.
    3. Figures 2-4  plot the absolute value of the  pitch, roll, and focus errors versus azimuth and zenith angle. You can see the two za strips plus the two azimuth swings. For pitch and roll 1 tick mark is .03 degrees. For focus 1 tick mark in .3 inches. The angle is set so that 180 degrees from pointing up is 50% of the maximum error. The za values of 19.6 and 10 at azimuth of 242.87 were repeated three times (twice with the azimuth spin and once with the za strip). The points 19.6 and 10 za at azimuth of 302.87 were repeated twice. These pitch values vary by about 8% max. The roll value lie on top of each other. The focus error varies by up to 14 %.
    4. The last figure shows the motion of the platform about 1256.35 feet as measured by the distomats while the survey was being taken. The maximum motion was .2 inches so using 1256.35 feet as the average value will not create large errors.
    5. processing:survey/010809/reducR/

    Fitting the pitch, roll, and focus.  (top..)

        The pitch, roll, and focus measurements were fit to a cubic in (za-10) degrees and 1,2, and 3 az terms in azimuth. The figures show the az,za  fits.
    1. Figure 1 has the pitch data (black) and the fit (red).
    2. Figure 2 is the roll data (black) and the fit (red). This fit is pretty good.
    3. Figure 3 is the focus data (black) and the fit (red). A different  fit was used for focus. It used (za-10) for the za variable. It was 3rd order in (za-10) for the za part. The az terms had 1a,3az and sin(za-10)*[cos(3az)+sin(3az)].
    4. The last figure shows the azimuth terms of the fits (1az,2az,3az) as well as the fit coefficients. The rms for the fits are: pitch .013 degrees, roll .0085 degrees, and focus  .13 inches. The 1az term of .028 degrees for pitch  may be from the horizontal offset of the platform. This offset should not give a roll term so i don't know where the .035 deg 1az roll term is coming from. When the tilt sensors were run on 04aug01 the 1az term was .003 for these tiedown positions. The 3az term for pitch and roll is similar to what we measured back in feb00 and what the tilt sensor measured in 04aug01. The fit to focus is what will be used to compute the focus error over the entire dish (since the tilt sensors don't measure focus).
    5. processing:survey/010809/reducR/
        This data will be used to connect the pitch and roll centered on the reflector to the pitch and roll as measured by the tilt sensors. We can get a complete sampling of az, za with the tilt sensors to help us with the model. We use the the reflector based  data to remove any offsets that the tilt sensors have.
    processing: survey/010809/reducR/ for initial analysis.