1. MMT Observatory 3rd Trimester 2008 Elevation Tracking

2. Tracking Data Collection
Data is automatically collected on the mount computer for every slew, and at 10-minute intervals during tracking. Tracking data is sampled at 100Hz for 120s.
A back-end matplotlib routine based on a reduction routine written in Matlab m-code reduces the previous night’s data and writes it to the MMTO MySQL database every morning.
The reduced data, along with relevant wind data and skycam images, can be viewed via a webpage here:

3. Webpage Display

4. Sample Reduced Tracking Data

5. Tracking File Issues

6. RMS Error Statistics
A combined MySQL query for tracking data over the dates of interest, at least 120s long, with the wind data correlated to the timestamps of the tracking files, produced 5064 members for the 3rd trimester of The RMS error statistics of the whole population were, in arcseconds:
Min
Max
Median
Inter-Quartile Range
0.007”
1.76”
0.072”
0.056”

7. RMS Error Histogram

8. RMS Error Totals

9. RMS Error, Guarded Data

10. Error Distributions
To investigate the influences of tracking velocity, position, and wind, both the complete population and outlier-trimmed populations were sorted and plotted as histograms. The distribution data were separated out as functions of velocity, position, and wind speed, as well as relative wind angle and speed.

11. RMS Error and Velocity

12. RMS Error over Elevation

13. RMS Error over Azimuth

14. Wind Data from Vaisala 4

15. Wind Speed and RMS Error

16. RMS Error over Wind Speed

17. RMS Error over Wind Angle

18. RMS Error with Relative Wind and Elevation

19. RMS Error with Wind Angle and Intensity

20. Conclusion
Median elevation RMS tracking error was 0.065”, with a spread of ±0.04” (using guarded data).
A lower limit to tracking smoothness, related to encoder quantization and friction, exists at about ±2 encoder counts, or ±0.02”.
Wind rejection could be tweaked; tracking degradation is strongly correlated with increasing wind intensity. Tracking at and below ~15mph is good.
Positions at high elevations away from the prevailing wind are more favorable for good tracking.
More study is needed for explanation of the poor tracking entries in the data population.