Presented at the 2012 International Geoscience and Remote Sensing SymposiumAquarius is a passive microwave radiometer operating at L-band that is designed to measure ocean salinity. Launched in June 2011, the instrument has since been the subject of on-orbit calibration to evaluate its performance and characterize its stability. This study addresses external calibration methods, using observed antenna temperatures to characterize instrument behavior by computing the oceanic global average and vicarious cold statistics. Results indicate that a slow drift in antenna temperature is present throughout the mission, as well as shorter time scale variations. Implementation of a noise diode deflection ratio-based correction algorithm mitigates most of the short term variations but the slow drift remains present in both statistics. It is most apparent using the global average statistic. The drift can be largely removed by adjusting the instrument calibration to force agreement between observed and modeled global averages over long time intervals.