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The magnificent Chilean Andes as seen from the CCAT Observatory site on Cerro Chajnantor

The magnificent Chilean Andes as seen from the CCAT Observatory site on Cerro Chajnantor

Descending from the summit

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Cerro Chajnantor Station Position


On 2006 May 11, a commercial Global Positioning System navigation receiver (Garmin GPS 35PC) was installed in the equipment shelter on Cerro Chajnantor to provide an absolute time reference for the instrument computer. The receiver antenna is mounted about 1.5 m above the ground level.

Since installation, the GPS receiver position has been recorded every 15 minutes. From these data, a high accuracy position has been determined for the station. ALMA Memos 261 and 312 discuss the analysis method and limitations for similar measurements made since 1998 November with a receiver mounted on the NRAO instrument container located at the ALMA site on the Chajnantor plateau. The table and figures below correspond to those in ALMA Memo 312.

Table 1. Cerro Chajnantor Station Position
  WGS 84 † SAm 56
Latitude [South] 22° 59'   8.30" ± 10 mas 22° 58' 55.3"
Longitude [West] 67° 44' 25.00" ± 10 mas 67° 44' 18.7"
UTM Zone 19: Northing 7 457 516 m ± 0.3 m 7 457 880 m
Easting 629 119 m ± 0.3 m 629 308 m
Altitude (receiver) 5611.8 m ± 0.3 m


† Uncertainties estimated from Figure 6.

Figure 3. Measured positions of the equipment shelter on Cerro Chajnantor, Chile, after 2006 May 11. 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. Measured positions and linear cross correlation coefficients. Note scale difference between latitude-longitude and altitude; 0.1" corresponds to 3.1 m.

Figure 5. Diurnal variation of measured positions. Note scale difference between latitude-longitude and altitude; 0.1" corresponds to 3.1 m.

Figure 6. Variance in the mean positions for successively longer sets of measurements. The error bars illustrate the sampling uncertainty for a normal distribution, σs/σ = [2/(N-1)]1/4 (Bailey 1971). The dashed lines show the decrease with N1/2 expected for sequentially uncorrelated data.

Graphics format: acrobat (pdf).