Modeling the  azimuth pointing errors



Intro  top

        The pointing model residuals have coherent errors in the azimuth axis. We should be able to remove them and improve the fit by:
    This page looks for other terms to add to the current model fit. The steps were:
  1. Use the raw pointing errors that were used as inputs for model 15 (apr04). They are great circle errors on the sky in units of arc seconds.
  2. Fit for some basic terms that have physical significance and then remove them from the raw data:
  3. See if the azimuth encoder rack gear runout error corresponds to the errors.
  4. Look at the tilt sensor roll residuals to see if they correlate with the pointing errors.
  5. Take into consideration the za dependence in the mapping of the platform tilt to the error on the sky.

The Measurements   top

    A simple fit to the raw errors was done to remove the large scale errors. The fit in azimuth  was:
    The plots show various steps in fitting the model 15 input errors (.ps) (.pdf) :

Conclusions  top

To do:

  1. write program to compute pointing errors for various physical motions of the telescope (rotating platform, translating in x,y, etc..)
  2. Using program in 1, see where the 1 az  and 3az terms  really come from. Should there be a za dependence in the 1, 3az terms for az errors?
  3. look at the tilt sensor data. Use program in 1 to see if the pointing residual errors correlate with them

processing: x101/model/azenctbl/

page up
home ~phil