The telescope observes from the southern slopes of Cerro Toco in northern Chile, near the town of San Pedro de Atacama. The site, belonging to the Universidad Catolica de Chile, was made available through the generosity of Prof. Hernán Quintana, Dept. of Astronomy and Astrophysics. The proposed ALMA site is nearby.
NRAO has performed extensize site testing using a weather station, a 225 GHz tipper radiometer, and an 11 GHz interferometric phase monitor. Summaries of these data are available at NRAO. These data were crucial in our decision to observe from Cerro Toco.
Using these data, Tom Herbig put together an approximate picture of the atmospheric conditions for observing at the site:
We intend to present a more sophisticated analysis derived from the TOCO datasets in the near future. In the meantime, here is a plot of the atmospheric emission and DC levels for the Ka2 and D1 channels (raw data: Ka2, D1).