Abstract

A passive, multi-channel microwave radiometer includes an antenna-lens assembly for receiving, and a first waveguide designed to provide a common path for propagating, 23.8 GHz and 31.4 GHZ atmospheric signals. The 23.8 GHz signal is above the frequency of relative maximum water vapor absorption and the 31.4 GHz signal is near a relative minimum in the water vapor absorption spectrum. Circuitry is responsive to the atmospheric signals for generating output signals representing the respective water vapor and liquid content in and the temperature of the atmosphere. For realtime calibration a blackbody assembly is mounted in the near field of the antenna-lens assembly. The blackbody assembly emits known blackbody microwave signals at 23.8 GHz, 31.4 GHz and in the V band. The radiometer is calibrated during its normal operation by causing a mirror to select the blackbody signals for propagation along the common path. The circuitry responds to the blackbody signals to represent them as first blackbody reference signals. A factory calibrated noise diode assembly adds a known noisy microwave signal to the first waveguide when a blackbody signal is being processed. The circuitry separately responds to such combined blackbody and noisy signals to separately generate a second blackbody reference signal. These first and second blackbody reference signals and the known temperature of the blackbody assembly are used to provide realtime calibration data that is used in realtime to obtain the output signals in response to the atmospheric signals.

Other References

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