Theodolite survey of dome from ao9 monument (origin=AO9)

aug,2001

The dome position was surveyed from the ao9 monument on 9aug01 starting at about 10pm. This page shows the results using AO9 as the origin. See ao9 survery (reflector as origin) for the results relative to the center of the reflector. The dome was moved through the following positions:

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).
a za strip from 19.6 to 1.09 degree in 1 degree za steps at an azimuth of 302.87 degrees.
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.
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 theodolite az and za positions-->platform offset from AO9.
The pitch, roll, and focus errors versus az and za.
Fitting the pitch, roll, and focus.

Differences between the encoder and theodolite az and za positions-->platform offset from AO9. (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. The correction was then added to the theodolite azimuth encoder values. The position differences (theodolite - encoder) are shown in the plots:

The first figure is the azimuth differences plotted versus za (top) and azimuth (bottom). These are great circle azimuth (the difference has been multiplied by the sine of the zenith angle). The bottom plot contains a sin fit to the 1az term for both of the spins. The offset, amplitude, and phase of the peak are printed.
The second figure plots the zenith angle differences versus za (top) and azimuth (bottom). The bottom plot also contains a fit to the 1az terms of the swings. The the amplitude for the az swing at 19.5 degrees is 80 asecs instead of the 88 for the other 3 fits. Looking at the fit, the peak to peak excursion is closer to an amplitude of 88 asecs so the sine wave probably got messed up a bit.

processing:survey/010809/pltazzadif.pro

The azimuth rotates about the main bearing. The bearing is offset relative to the AO9 monument where the theodolite was positioned. This offset causes a 1 azimuth term in the differences of the measured azimuth positions. The difference was computed as TheodoliteZa-encoderZa (and similar for az values). By definition the peak of the sine wave has the theodolite angle greater than the encoder angle. For this to occur (using the za data), the distance from AO9 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 88 arc seconds was 2.23 inches. Projecting this along the phase direction of 6 degrees gives the offsets of the platform relative to AO9:

radial offset of platform	dx offset (east positive)	dy offset (north positive)
2.23 inches	.2 inches	2.2 inches

The platform offset will create a pointing error. The raw pointing errors that were used to build model13 (jan02) agree with the measured translation:

pointing error amplitude,phase	offset error ampltidue,phase
za: 98 asecs, 185 degrees	za: 88 asecs, 5 degrees
az: 98 asecs, 94 degrees	az: 88 asecs, 277 degrees

The pointing error is the direction you must move the telescope to correct for the pointing offset. It is 180 degrees from the direction of the motion and the amplitudes are within 10%.

processing: survey/010809/reduc/cmpao9offsets.pro

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:

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.
Figure 1 bottom is the same errors plotted versus azimuth angle.
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 %.
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 so the platform was relatively stable during the measurements.

processing:survey/010809/reduc/pltprf.pro

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.

Figure 1 has the pitch data (black) and the fit (red). The fit is good except for the bump at za of 8 degrees, 1 degree, and za >= 19.

Figure 2 is the roll data (black) and the fit (red). This fit is pretty good.

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)].

The last figure shows the azimuth terms of the fits (1az,2az,3az) as well as the fit coefficients. The rms for the pitch fits are: pitch .013 degrees, roll .0085 degrees, and focus .1 inches. The 1az term of .02 degrees for pitch and roll may be from the horizontal offset of the platform. 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).

processing:survey/010809/reduc/pltfit.pro

The fit data will eventually be used to connect the pitch and roll of the theodolite 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 theodolite data to remove any offsets that the tilt sensors have.

todo:

Do some more tilt sensor azimuth swings to make sure that the platform is not tilted. The tiedown encoders were changed back in sep01 (lightning) and we should verify that the tiedowns were set back to the same values.

processing: survey/010809/reduc/doit.pro for initial analysis.

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