Radiometric Phase Correction

We analyze the technique of using radiometers to measure the precipitable water vapor (PWV) content of the atmosphere in order to correct interferometric data for phase noise due PWV fluctuations in the troposphere. We present an idealized model of phase fluctuations due to PWV variations in the troposphere based on the Taylor hypothesis, and we summarize the radiometry equations. We then consider various options for radiometric phase corrections, including: (i) the very demanding technique of making an absolute measurement of PWV at each antenna assuming an accurate (absolutely calibrated) measurement of brightness temperature, TB , and using a theoretical model for the troposphere and measured physical parameters for the troposphere (temperature, pressure, etc...), and (ii) the less demanding technique of using a strong celestial calibration source to derive an empirical relationship between brightness temperature fluctuations and atmospheric phase fluctuations. Radiometric phase cor..