We report measurements of the atmospheric opacity of the South Pole at 225 GHz for the period from day 3 to day 180 in 1992. These opacity data were derived from continual radiometric measurements of the sky-brightness temperature as a function of the zenith angle. These radiometric measurements were performed with a 225-GHz heterodyne atmospheric radiometer on loan from the National Radio Astronomy Observatory. This radiometer was previously used to characterize other candidate millimeter and submillimeter radio-telescope sites. We found that the atmospheric opacity was below 0.098 air mass−1 75% of the time from day 3 to day 70 in 1992, and below 0.055 air mass−1 75% of the time from day 70 to day 180 in 1992. Thus, our data demonstrate that the South Pole is an excellent site for performing millimeter- and submillimeter-wavelength radio astronomy.
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