The fluctuation of VLBI visibility phase can be occurred, predominantly caused by the irregular distribution and motion of water vapor in the atmosphere at high frequencies (>1GHz). This radio-seeing effect shows up on filled-aperture telescopes as an anomalous refraction (AR).
This can be shown as if the antenna pointing-offset increases, in other words the apparent displacement of radio sources from its nominal position happens.
We carried out the single-dish observations on KVN sites in order to check the effect of AR from 2010 to 2014. Orion KL, U Her, and R Leo were observed with 1second sampling time at 22.235GHz and 43.122GHz simultaneously. Each source was observed with the tracking mode for 30 minutes per a source.
We analyzed the structure function, power spectrum and Allan variance of the data according to a day and a night, a season and observatories.
Finally, we can infer that the AR effect depends on the atmospheric environment, especially tropospheric turbulence.