A dual-frequency microwave radiometer has been developed to remotely sense water vapor and liquid in the troposphere. An optimum frequency pair, 20.60 and 31.65 GHz, is adopted. The system consists of two Dicke radiometers (one at each frequency), both of which are controlled by a microcomputer system and mounted on a rotatable pedestal. The sensitivity at 1 s time constant and the accuracy of the brightness temperature are 0.2 K and 0.5 K, respectively, at each frequency.

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