Chajnantor GPS Receiver
In 1998 June, a commercial
Global Positioning System
navigation receiver
(Garmin
GPS 35PC)
was installed on the roof of the NRAO instrument container at Chajnantor
to provide an absolute time reference for the
instrument computers.
The receiver antenna is mounted at the top of a solar panel bracket,
about 3.26 m above the ground level.
Starting at 1998 November 26 UT 19:30, the GPS receiver position
has been recorded every 15 minutes. Intentional degradation of
GPS signals (Selective Availability) was discontinued at
2000 May 2 UT 4:00.
Measurements recorded through 1999 April 1 UT 17:30 are analyzed in Memo
261
and measurements through 2000 June 7 UT 16:56 are analysed in Memo
312.
The figures below update the corresponding figures from
Memo 312 with
data recorded 2000 May 2 UT 4:00 through
2001 February 6 UT 14:13. See Memo 312 for discussion.
| Table 1. Chajnantor Position |
|
WGS 84 † |
SAm 56 |
| Latitude [South] |
23° 1¢ 22.42² |
± 50 mas |
23° 1¢ 9.42² |
| Longitude [West] |
67° 45¢ 17.74² |
± 30 mas |
67° 45¢ 11.44² |
| UTM Zone 19: |
Northing |
7 453 408 m |
|
7 453 773 m |
| Easting |
627 583 m |
|
627 772 m |
| Altitude |
receiver |
5062 m |
± 2.5 m |
| ground |
5058.7 m |
† Uncertainties estimated from Figure 6.
Figure 3. Measured positions of the NRAO equipment
container on Chajnantor, Chile, after 2000 May 2 UT 4:00,
when SA was discontinued.
In the right panels, the histograms show the actual distribution
of the measured positions
and the curves are normal (Gaussian) distributions for the
parameters derived from the data. Note scale difference between
latitude-longitude and altitude.
Figure 4. Positions measured after discontinuation of SA
and linear cross correlation coefficients.
Note scale difference between
latitude-longitude and altitude; 0.1² corresponds to 3.1 m.
Figure 5. Diurnal variation of positions measured
after discontinuation of SA.
Note scale difference between
latitude-longitude and altitude; 0.1² corresponds to 3.1 m.
Figure 6. Variance in the mean positions
for successively longer sets of measurements
after SA was discontinued.
The error bars illustrate the
sampling uncertainty for a normal distribution,
ss/s = [2/(N-1)]1/4 (Bailey 1971).
The dashed lines show the decrease with N1/2
expected for sequentially uncorrelated data.
Figures in gif and compressed postscript (.ps.gz) format.
Last modified 2001 March 7
Simon Radford