Proceedings PaperMeasurements of anomalous refraction and tip-tilt compensation at millimeter wavelengths
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Radio seeing shows up on filled-aperture telescopes as an apparent displacement of a radio source from its true position, known as anomalous refraction (AR). The magnitude of this effect, as a fraction of the beam width, is bigger on larger telescopes. Here we report the partial results of systematic AR measurements conducted with the 14 m telescope of the Five College Radio Astronomy Observatory. The measured values range from approximately equals 2' (winter) to approximately equals 20' (summer). These data indicate that the pointing accuracy of large telescopes will be limited by tropospheric turbulence. We therefore discuss the basic concept and preliminary design of a tip-tilt compensation system at millimeter wavelengths that would use a 183 GHz radiometer as a wave front sensing device, capable of recovering most of the turbulence-induced pointing error.