Characterization of autoemission reflection for precise radiometer calibration

Calibration of spaceborne microwave radiometers to precisions required for assessing climate trends requires biases less than 0.05 K to be identified. The use of warm pyramidal blackbody targets closely coupled to the radiometer antenna to establish thermal reference points has become standard for this purpose, although the effects of small standing waves generated by the radiometer itself can be considerable. We show these effects using a 55GHz radiometer and precision scanned pyramidal target, along with coherent processing of the detected power. The study illustrates the importance of the radiometer front-end architecture in minimizing standing wave biases.