A Site Survey for Large Millimeter/Submillimeter Telescope

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Future large radio telescopes, such as Large Millimeter and Submillimeter Array (LMSA) planed by Japan, need a construction site having the following atmospheric, meteorological, and geographical conditions to bring out the capability of the telecopes to the full extent and to get many good observational results with the telscopes : 1) low opacity (i.e. high transmission) of the atmosphere even at submillimeter wavelengths, which means a high altitude place, 2) good radio seeing to achieve 0.1-0.01 arcsec resolution, 3) less windy place as possible to achieve good pointing of antennas, 4) flat or gently sloped area of more than 2km sqaure to place and move 50 antennas.According to these conditions, the present candidates of the LMSA site are Mauna Kea in Hawaii and high plateau in northern Chile.For these two potential sites, we researched atmospheric conditions (radio transmission and radio seeing), the meteorological conditions, and the geographical conditions.In order to measure atm … More ospheric and meteorological conditions in the northern Chile, we installed two 220 GHz radiometers, two sets of radio seeing monitors and four meteorological stations to the sites with altitudes of 2400-5000m and mesured these conditions from 1995 to 1996.The results of the measurements are in the following.1) Mt.Paranal (2600m) area in the northern Chile has a good atmospheric and meteorological conditions, although the altitude is not so high (2600m) and one of good sites for millimeter-wave observations.However, the area is not good site for sub-millimeter wave observations.2) There are very dry high plateaus (with an altitude of 4000-5000m) in the northern Chile.The high plateaus have extremely good atmospheric and meteorological conditions : 50% of a year can be used for sub-millimeter observations and radio seeing is as good as typically 0.5 arcsecond.It is concluded that the atmospheric and meteorological conditions in the high plateaus are statistically better than those of Mauna Kea (altitude is 4100m) in Hawaii. Less