A Site Survey for Large Millimeter/Submillimeter Telescope

未来的大型射电望远镜，如日本计划的大型毫米波和亚毫米阵列(LMSA)，需要一个具有下列大气、气象和地理条件的建筑场地，以充分发挥望远镜的能力并获得许多良好的观测结果：1)即使在亚毫米波长，大气的低不透明度(即高透射率)，这意味着高海拔地区；2)良好的射电可见度，以达到0.1-0.01弧秒的分辨率；3)尽可能少的风的地方，以实现天线的良好指向，4)平坦或缓坡面积超过2平方公里，可放置和移动50个天线。根据这些条件，目前LMSA选址的候选地点是夏威夷的莫纳克亚和智利北部的高原。针对这两个潜在选址，我们研究了大气条件(无线电发射和无线电收看)、气象条件和地理条件。为了测量大气…为了使智利北部的大气和气象条件更好，我们在海拔2400-5000米的地区安装了两台220 GHz辐射计、两套无线电视宁仪和四个气象站，并于1995年至1996年对这些条件进行了测量。测量结果如下：1)智利北部的帕拉纳尔山(2600m)地区的大气和气象条件较好，虽然海拔不是很高(2600m)，是进行毫米波观测的好地点之一。然而，在智利北部的帕拉纳尔山(2600m)地区，虽然海拔不是很高(2600m)，但也是进行毫米波观测的好地点之一。然而，在智利北部的巴拉纳尔山(2600m)地区，虽然海拔不是很高(2600m)，也是进行毫米波观测的好地点之一，但测量结果如下该地区不适合亚毫米波观测。2)智利北部有非常干燥的高原(海拔4000-5000m)。高原具有极好的大气和气象条件：一年有50%的时间可以用于亚毫米波观测，无线电可见度通常可达0.5角秒。结论是，在统计上，高高原的大气和气象条件好于夏威夷的莫纳克亚(海拔4100米)。较少

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