Pointing model gradients

• If you move by the slew speed (maximum velocity) in 1 second, how much does the model change.
  
• This can be useful if you want to evaluate the model correction for the current az,za but you have the az,za  position of the previous  second.
• Measure the model correction at az,za, subtract the model correction, and then recompute the model correction for the new az,za. How much does the model correction change?
  
• This is useful if you want to remove the model correction from then az, za measured by the encoders.
• The encoder position already has the model correction included. You really want to know the model correction for the az, za before the correction is added.

An az,za grid of 1 degree steps in za and 5 degree steps in az were used to evaluate the model.
The plots show the changes in the model correction for various steps (.ps) (.pdf) :

•  Top: the model errors vs za. Black is error in az, red is err in za. The vertical spread comes from the az going 0 to 360.
• 2nd: The change in the model Az,Za errors when the az, za motion is .4deg and .04 degrees. This is the maximum that the az,za can move in 1 second.
• 3rd: The change in the az, za errors if you move the az,za position by the model error at that position.
• Bottom: The total error for the 2nd and 3rd plots. The az, za errors have been added in quadrature.
• Page two shows the same changes plotted versus azimuth.

Conclusions:

• You can probably ignore the changes at za=2,3 degrees since you spend little time their.
  
• If you evaluate the model 1 slew step away, the largest error is around 2 asecs.
• If you evaluate the model without removing the model correction, you can be off by about 1 asec.
  

page up
home ~phil