990128 report
Pointing: update central bearing solution (19990128)
January 28, 1999
A NEW 'EMPIRICAL' SOLUTION WAS INSTALLED AT THE TELESCOPE ON 27-JAN-1999 AT
15:33:12.09
19990124 Measurements
The plot below shows pointing observations of 990124 without the
empirical correction active The plot shows the (green), with at the bottom the residuals
(red line) resulting from the current
empirical solution (black line).
The blue lines show the new model and
the new residuals for the best dataset: the horizon errors over the
range of the CB feature are within 1".
As an independent test, the magenta
line in the bottom plot shows the residuals applying the new
solution to a 19990120 data set. Because this data set was very
noisy (weather and source strength), I smoothed it in AZ. Nevertheless
the new solution also appears to agree well with those data: the residual
horizon error is less than 2".
Check on new empirical correction for central bearing defect
SUMMARY:
The new empirical corrections for the central bearing defect
are tested and appear to work well.
The last measurements ( 990124 )
, confirmed the empirical correction to be overestimating the current
size of the defect. A new version of TEL_EMPIRICAL.DAT was installed
yesterday (1/27/99 15:33) and tested here by tracking 3c120 from
(az,el) = (117,61) at HST 18:44 to (130,69) at 19:22, with the
correction enabled. The pointing residuals are shown below :
The rms scatter in the elevation residuals is 0.6".
There is a linear baseline trend in daz,
but no obvious sign of systematic residuals near az=125,
where the defect is expected to occur. Given the elevation
at the time (66 degs), azimuth pointing errors
resulting from the new model, at the horizon, may therefore be
estimated as < 1.8"/cos(66) = 4.4" at the 3-sigma level.
Please address any comments,
suggestions or requests to:
Iain Coulson
28 Jan 1999
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