Satellite radiometer pre-launch sensitivity estimation using anechoic chamber and channel inter-comparison

The sensitivity of a radiometer to the brightness temperature variations of the target is one of the critical parameters of any radiometric measurement. The sensitivity is limited by the noise in the measurement and the stability of the instrument. In this study measurements in an anechoic chamber are used to evaluate the sensitivity limit of radiometers, which are the noise injection radiometers of European Space Agency´s SMOS (Soil Moisture Ocean Salinity) satellite. The sensitivity is especially important for the measurement of sea surface salinity (SSS), one of the retrieval objectives of SMOS. The methods used include comparisons of the measurements to the physical temperature estimation of the chamber, both in relative and absolute sense, and comparison of different radiometer channels with each other. The analysis demonstrates the reliability of the methods in consistency of both brightness temperature values and physical temperature measurements. Finally, the results show that the noise injection radiometers satisfy the measurement requirement for SSS retrieval.