Presented at the Global Ocean Salinity and the Water Cycle WorkshopKey Aquarius science objectives were to (1) map the mean SSS field, (2) measure the annual SSS cycle, and (3) document interannual variations, within a three-year minimum duration. This presentation addresses objectives (2) and (3) by analyzing the radiometer calibration drift on these time scales using co-located in situ data. The analysis converts the in situ data to an expected radiometer brightness temperature (Tb), and differences these from the Aquarius radiometer Tb. The crux of the analysis is separating the sensor drift from the varying environmental corrections in the retrieval algorithm. The approach is to take differences between geographical zones and regression analyses to isolate the sensor variations from the environmental ones. I will explain this calculation and present the results achieved until now with this work-in-progress. Calibration curves for each of the six Aquarius radiometer channels are derived, and are sensitive to the calibration method used in the processing for a few algorithm test versions being evaluated for the new V5.0 data release. Understanding the residuals due to environmental model errors remains more problematic. The future goal will be to adapt the technique to SMAP, and eventually SMOS measurements to enable a systematic cross-calibration of the different satellite systems and obtain a reliable combined multi-year time series for studying ocean trends.