MMT Observatory 3rd Trimester 2008 Elevation Tracking

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: http://hacksaw.mmto.arizona.edu/plots/tracking/plots.php

Webpage Display

Sample Reduced Tracking Data

Tracking File Issues

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 2008. 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”

RMS Error Histogram

RMS Error Totals

RMS Error, Guarded Data

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.

RMS Error and Velocity

RMS Error over Elevation

RMS Error over Azimuth

Wind Data from Vaisala 4

Wind Speed and RMS Error

RMS Error over Wind Speed

RMS Error over Wind Angle

RMS Error with Relative Wind and Elevation

RMS Error with Wind Angle and Intensity

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.