A transportable 16-GHz solar telescope for atmospheric transmissivity measurements

A transportable, 16-GHz solar telescope is now being used to investigate the atmospheric transmission of solar radiation, with special emphasis on the effects of precipitation. An equatorial mount and digital-clock drive direct the pointing angle of the antenna to follow the sun's path to within 0.05° of arc. A 40-inch offset paraboloid antenna with twin prime focus feeds is used. The dual feeds alternately sample (at a 1-KHz rate) the transmitted solar energy and the atmospheric emission, so that the detected difference signal is a direct measure of the atmospheric transmissivity. The superheterodyne, double-sideband receiver has an approximate overall noise temperature of 740°K and IF bandwidth of 225 MHz. Attenuations up to 35 db can be measured. The fast switching rate along with a high-speed data-acquisition system allow measurements with a time constant less than 0.1 sec. The transportability of the instrument permits studies of attenuation in various climatic regions.