Measurement of Atmospheric Attenuation at 1.3 and 0.87 mm with an Harmonic Mixing Radiometer

The atmospheric attenuation at 1.3 and 0.87 mm was measured above Mount Hamilton, California in the period December 5 to December 9, 1973. The measured value of the zenith attenuation varied from 1 to 5 dB at 1.3 mm over this five-day period, and was 2.5 dB at 0.87 mm on December 9, 1973. The total beamwidth of the 120" Lick Observatory telescope used in the Coude configuration was measured to be 3\´ at 1.3 mm.