Further analysis of elevation pointing

The table below shows the pointing data of the last few months which ought to have revealed such a trend . These data are identified by typically having

• a sufficiently large size (N-points > 10 )
• an uncomfortably large residual elevation pointing error ( rms-del > 2.0" ), particularly when compared to that for azimuth
• a sufficiently large span of temperature or front-to-back temperature differential.

1. the dataset - by date
2. the FE
3. the number of data
4. the raw rms scatters in daz
5. the raw rms scatters in del
6. the slope of the best fit line in the del - vs- (Tf-Tb) plane
7. the rms scatter of del about this line
8. the slope of the best fit line in the del - vs- 0.5*(Tf+Tb) plane
9. the rms scatter of del about this line

      1       2  3     4   5        6         7         8          9

  dataset    FE  N    raw rms    del-vs-  new_rms     del-vs-   new_rms
                      daz del    (Tf-Tb)            0.5*(Tf+Tb)

  961011_17   S 26    1.1 1.5  -6.2 +- 7.4   1.5    1.3 +- 1.6    1.5    
  961128_01   A 12    1.9 1.8   4.2 +- 4.7   1.7    1.3 +- 0.6    1.5
  961207_20   B 21    1.8 2.0  -6.4 +- 2.1   1.7    1.1 +- 0.9    1.9
  961218_16   B 10    2.1 2.0   3.7 +- 1.4   1.5    0.8 +- 0.3    1.5

  970127_01   A 17    2.1 3.9  -5.5 +- 0.9   2.2   -4.3 +- 0.6    2.0
  970130      B 15    3.4 3.6  20.3 +-12.1   3.3   -2.0 +- 1.2    3.3
  970201-03   B 17    4.0 3.6  15.0 +- 8.6   3.3    1.4 +- 0.6    3.0
  970207_20   A 84    2.8 3.7   2.8 +- 6.2   3.7    3.4 +- 0.2    1.6   *

  970223_05   A  7    1.3 3.2   3.7 +- 1.2   2.1    2.5 +- 0.5    1.5   *c
  970228_16   A  9    2.0 2.8  -4.4 +- 5.0   2.7   -1.5 +- 1.5    2.7
  970306-07   A  7    1.7 2.4   0.6 +- 2.2   2.4    0.5 +- 0.4    2.1
  970309_05   B  6    1.2 2.4   2.4 +- 0.9   1.7    1.2 +- 0.4    1.5   *c

  970312-13   A  8    1.2 2.7  18.0 +- 4.6   1.6    1.3 +- 0.4    1.8
  970313_17   A 10    1.9 3.8   9.5 +- 2.0   2.1    2.2 +- 0.8    2.9
  970319_17   B  8    1.4 4.0  10.0 +- 1.3   1.4    4.5 +- 0.9    2.0 
  970321_05   A  7    2.2 4.7  12.6 +- 0.7   0.9    0.1 +- 0.6    0.9    c

  970325_21   A 34    1.6 2.4  11.8 +- 3.0   2.0    0.1 +- 0.4    2.0
  970401_01   A  6    1.9 4.2  18.3 +- 4.4   2.1   -1.2 +- 1.1    2.0
  970405_07   S 29    2.1 4.5  18.3 +- 1.7   2.0    0.0 +- 1.0    2.0    c
  970405      S 70    1.3 2.9  11.6 +- 1.0   1.7    0.2 +- 0.2    1.7
  970406_02   S 18    2.4 4.2  15.9 +- 1.3   1.4   -0.1 +- 0.5    1.4    c

  970406-07   S 28    1.5 3.2   8.0 +- 2.6   2.8    1.1 +- 0.3    2.2   *c
  970407-08   S 25    1.9 3.0   4.1 +- 4.5   3.0    1.0 +- 0.2    2.0   *
  970408_17   S 75    1.3 2.3  12.7 +- 0.7   1.0    0.7 +- 0.3    1.0   

  970409_18   S 42    1.9 2.3   3.2 +- 0.9   2.0    0.9 +- 0.3    2.0
                                                    0.0 +- 0.3    2.0

  970416-17   B 13    0.7 1.3   2.5 +- 3.1   1.2    0.7 +- 0.2    0.8   *
                                                    0.7 +- 0.1    0.7

  970420      S 15    1.3 2.3   4.7 +- 1.0   1.4    1.1 +- 0.2    1.1   *c
                                                    0.3 +- 0.2    1.3    

  970424_01   A 12    0.5 1.6  -6.0 +- 2.5   1.3    1.2 +- 0.5    1.3
                                                    0.7 +- 0.4    1.2

  970425_01   S 11    0.5 1.7 -13.0 +- 2.7   1.0    2.4 +- 0.4    0.7   *
                                                    0.4 +- 0.4    0.9

  970425-26   S 17    1.2 2.2  -4.1 +- 1.9   1.9    1.0 +- 0.2    1.2   *c
                                                    0.9 +- 0.1    1.1   

  970426_17   S 16    1.6 2.3   4.6 +- 2.1   2.0    1.4 +- 0.2    1.0   *c
                                                    1.0 +- 0.2    1.4   

  970428_20   S 10    1.3 1.3   6.3 +- 3.0   1.1    1.3 +- 0.3    0.7   *
                                                    0.5 +- 0.4    1.0

  970501-02   S 15    1.4 1.8   1.3 +- 1.8   1.8    0.8 +- 0.1    1.0   *
                                                    0.7 +- 0.2    1.2   

Note the following :

• Prior to 970320 the value of TEMP_SLOPE was 6.5"/deg. This parameter corrects elevation pointing for differential front-to-back leg temperatures. On 970320 the value of TEMP_SLOPE was incorrectly adjusted to 16.5"/deg, and on 970409 it was adjusted to 3.5"/deg. The elevation data between 970320 and 970409 have therefore been corrected by the derived del-vs-(Tf-Tb) relationship before deriving the slope in the del -vs- 0.5*(Tf+Tb) plane shown here. The fact that the derived slopes in the 0.5*(Tf+Tb) plane are then essentially 0.0 shows that, within that period and prior to 970406, there was no observable trend .
• For data after April 09th the table shows the fit of del -vs- 0.5*(Tf+Tb) both before and after correction for the del-vs-(Tf-Tb) relation, in order to produce fits comparable with those for the period 970320-970409.
• An asterisk at the end of the line implies a significant improvement (reduction) in the scatter in del by fitting against 0.5*(Tf+Tb) when compared to either the raw residuals or to the fit with (Tf-Tb), and a >3-sigma determination for the slope of the line in the del-vs-0.5*(Tf+Tb) plane.
• A 'c' indicates that the data were taken while observing comet Hale-Bopp or in the 24 hours thereafter.

• The first observed instance of the trend occurred on 07 Feb, although comet-observing had been in progress before that.
• 3-days-per-week observing of the comet started in March, while it was occasionally being observed 2-days per week even in October 1996.
• There are 12 instances with significant trends , half of which are linked to comet observing, and there are 3 other datasets linked to comet observing where no trend is seen. So, 2/3 of comet-related pointing data for which this analysis is possible show the effect, while it occurs occasionally in other data.

There is insufficient data to suggest, for instance, that the effect lingers for some period after comet observing before disappearing. Continuous monitoring of the elevation pointing ought to reveal whether this effect is permanent or transient.

Return to POINTING REPORTS

Iain Coulson
05 May 1997