Results survey2. Compare with survey1 (M_SUR2,M_SUR\1)

19oct03 links to plots:

All 38000 targets were measured on mar01 (M_SUR1). After this the dish was adjusted. In oct-nov01 another set of pictures were taken (M_SUR2). These were measured and analyzed by the vstars software that came with the photogrametry equipment. The results became available in oct03. Lynn baker then fit a sphere to the targets and came up with a radial error for each target. For the plots below, I took the two data sets and used only the common targets from both surveys (37752 common targets).

The coordinate positions of the targets.. How they've changed survey1 to survey2. (top)

The targets have an x,y,z position using the center of the dish as the origin, x positive is east, y positive in north, and z positive is up. There is an associated measurement error computed by the vstars software. The two plots below show how the coordinate position of individual targets moved between the first and second surveys.

Fig 1 (1mb). Motion of the targets (survey2-survey1) vs position on dish. The top plot is versus x (east,west), the middle plot is versus y (north,south), and the bottom plot is versus z. For each plot the x,y,z differences are plotted in color: deltaX black, deltaY red, deltaZ blue. To keep the size of the file manageable i sorted the data by x,y,z smoothed by 5 and then decimated by 5. This reduced the scatter in the data, but the trends remained. The x coordinate of the targets moved by an average of 1.2 inches ramping from +.5 inches to +2 inches as you move west to east.
Fig 2 (1.8mb). Magnitude of the target position motion vs position on dish. This is the fig 1 data combined to just plot the magnitude of the target motion sqrt(deltax^2+deltay^2 +deltaz^2). It has not been smoothed so the scatter is that of the original data.
Fig 3 (1.7mb). The change in the measurement errors vs position on the dish. For each target the measurement error ( SigMeas=sqrt(sigx^2+sigy^2+sigz^2)) was computed for survey 1 and survey 2. Then the difference in the measurement error (sigMeasSurvey2 - sigMeasSurvey1) was plotted versus the x, y, and z coordinate of the targets. For most of the data, the errors were smaller on the second survey. The exceptions are points with z less than 10 feet (za le 9 degrees) and 50 feet north of the center were the errors have increased. This might be showing us the degradation of the targets with time.

The normal errors (radial direction) of the targets. (top)

The radial errors are the residuals from fitting a sphere to all of the measured targets. The sign convention is: positive means the target is too far from the center of curvature, negative is too close to the center of curvature.

Fig 4 (.4 mb). Survey2 radial errors arrow plot and fractional change. This only includes data with radial errors gt than 2 mm. The top of the plot is north, the left of the plot is west. There are many things coded in this plot:

The length of the arrow is proportional to the error (2mm per division). The arrows are clipped at 10 mm.
The angle of the arrow is computed from -Err2/Err1. 0 Degrees is perfect, -60 degrees is no motion, + 60 degrees too far times 1, -120 is turned the wrong way...
Color Red has not been corrected enough (also points to the left), black has been corrected too much. Green is ge 10mm (and clipped) blue is le 10mm (and clipped).

Fig 5 (.04mb) Histogram of radial error ratio Surv2/Surv1 (.ps) (.pdf).This is a histogram of the radial error Surv2/Surv1 using all the data.. The y axis is fraction of all targets (rather than number of targets). The histogram was binned to .02 mm. The jumps at -1,1,2 are flagged with what they are caused by. I'm not sure why there is a jump at 0 (maybe this is just a binning problem??). The histogram is centered at .1 so on average the correction was not enough by about 10%.
Fig 6 (.2mb) Image of survey2 radial errors.The image includes all the survey 2 points, not just the points common between survey1 and survey2.

top

The color bar at the top extends from -5 mm (blue) thru 0 error (green) to +5 mm (red). The black spots are missing targets. I interpolated the x, y projected target positions onto a grid of 3,1.5 feet using a tophat function with a radius of 3.4 feet. Some grid points have averaged together more than 1 target. The blue spots in the lower right stand out. They correspond to areas that were over corrected (see fig 5). The red ring at a radius of 200 feet stands out clearly (the moat??). Some of the red horizontal lines that go across the entire dish are probably the new east west cables that were installed during the upgrade. They are probably stretching causing them to sink lower.

Normal errors moving along the north/south cable direction. (top)

The panels are 3 by 6.25 feet and are mounted with the long direction east-west. Targets are positioned at the corner of each target. As you look down on the dish, the targets make columns running north/south spaced every 6.25 feet (161 columns in total). Every 25 feet a column of targets sits atop of one of the main support cables.
I arranged the targets in columns of constant X by sorting the 38000 targets in X (east/west) and then I found the locations where they jumped by 6.25 feet. Each of these columns was then sorted in Y (north/south).

Fig 7 This shows the normal error along each north/south column (.ps) (.pdf).The first plot is the west half of the dish while the second plot is the east half. Up is north and down is south. The lines are targets. Deflections left/right on the line are proportional to the normal errors. To the right implies the target is too low (the dish is sagging) to the left has the target too high. A deflection that equals the separation of two lines is 6.25 mm (each tick would be a normal error of 10 mm). The blue lines sit atop the main cables. The red lines are the target columns between the main cables. This plot will show the larger errors. Errors less than a few mm will not be apparent.

In general you can see that the targets over the main cables have much less scatter than the intercable targets.
Some patches have an oscillation on the intercable targets low,hi,low,hi as you move along Y. The adjacent cable targets do not show this.
The horizontal lines that point to the right (too low) are where new east,west cables have been installed. They must be relaxing. The targets over the main cables do not show this. At this point there should be a strong scalloping on the dish.
You can see some bad spots at X=100, y=50To100 where both the main cable and intercable targets are bad. This is where the cables cross the moat. For reference, td4 is at (166,-96). I looked at this spot of the dish and it looks like there are diagonal tieback cables that might block an adjustment trolley from passing thru. Figure 4 showed that some of these points did not change between survey 1 and survey2.

Fig 8 The median and rms normal errors along a north/south column of targets (.ps) (.pdf). After throwing out 3 outliers, I computed the median and rms of the normal error along each of the north/south columns (see fig 7). The top plot is the median of the normal error, the bottom plot is the rms of the normal error along each north south column. There are 161 columns spaced 6.25 feet apart. Every 4th column there the targets are above a main cable. The red * are above the main cables, the black * are in between the main cables. The median value shows a sag of up to .6 mm between the support cables. The rms (bottom plot) shows a larger variation as you move away from the column over the main cables (up to 2mm rms along the center column between two main cables). The west half of the dish shows a large variation of the rms than the east half. It also has a lower rms along the main cables than the east half. The large rms's around 50-100 feet are from the bad points at y=-150 to -200 in y.

processing: x101/dish/M_SUR/dorsur1_2.pro

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