Background emissions during cold sky calibration of Aquarius

The Aquarius instrument is a pathfinder to demonstrate the measurement of sea surface salinity (SSS) from space. The goal is to measure SSS with an accuracy of 0.2 practical salinity units (psu) and spatial resolution of 150 km, globally each month. To achieve this high accuracy in SSS, the radiometer requires accurate radiometric calibration. As part of the calibration plan it is planned to look at cold sky. The objectives of the Aquarius cold sky calibration (CSC) are to assist in the absolute calibration of Aquarius radiometer and to monitor calibration stability through repeated measurements. This manuscript describes the procedure being followed to identify optimum locations and times for the calibration. The goal is to find times with a stable signal from cold sky and locations around the orbit with a minimum contamination due to land and radiation from other external sources.