Development of a high stability L-band radiometer for the Aquarius ocean salinity mission

The NASA Earth Science System Pathfinder (ESSP) mission Aquarius, will measure global ocean surface salinity with ~100 km spatial resolution every 7-days with an average monthly salinity accuracy of 0.2 psu (parts per thousand). This requires an L-band low-noise radiometer with the long-term calibration stability of ≤0.1 K over 7 days. A three-year research program on radiometer stability has addressed the radiometer requirements and configuration necessary to achieve this objective. The system configuration and component performance have been evaluated with radiometer test beds at both JPL and GSFC. The research has addressed several areas including component characterization as a function of temperature, system linearity, noise diode calibration, temperature control of components and optimum switching of the Dicke switch for lowest noise performance. A breadboard radiometer, utilizing microstrip-based technologies, has been built to demonstrate this long-term stability. This paper will present the results of the radiometer test program and details on the design of the Aquarius radiometer. The operational sequence that will be used to achieve the low noise and stability requirements will also be discussed.