The calibration of the SMOS payload: MIRAS "Microwave Imaging Radiometer using Aperture Synthesis" is achieved throughout a combination of internal calibration modes and external manoeuvres to point the instrument to deep-sky. During the external manoeuvre the Noise Injection Radiometers (NIRs) located in the MIRAS' central hub structure, are accurate calibrated in order to use their measurements in nominal pointing to absolute calibrated MIRAS' measurements: images of Earth surface brightness temperature in Kelvin. The main NIR's calibration parameter is the internal diode noise temperature (Tna) which is estimated during external manoeuvre. Its variation directly affect the final level of brightness temperature image hence the need to monitor the Tna evolution since the beginning of SMOS mission. Further monitoring of MIRAS' absolute calibration is performed with in-situ L-band brightness temperature measurements over Concordia station in Antarctica (Domex experiment) and globally over Oceans by using sea surface emission forward model. Results of MIRAS calibration long-term monitoring are presented in the figures collection available here.
IDEAS+, SMOS team