Assessment of the Local Oscillator calibration frequency impact on the SMOS Sea Surface Salinity

The MIRAS instrument has a unique reference clock that is distributed to the Control and Monitoring units (CMN) located in the SMOS arms and in the hub. Each CMN uses the clock signal, provided by the Local Oscillator, to generate a reference tone and provide it to a group of six receivers. Although every CMN should generate exactly the same tone, the phase of the tones drifts due to the temperature dependency of the CMN electronics. A comprehensive analysis of the phase drifts with physical temperatures fluctuations was performed during onground characterisation [1]. The assessment of these phase drifts as a function of temperature changes was performed in [2], verifying that phase drifts could be mainly assigned to the LO temperature drifts. These phase drifts are adding noncoherent phase information to the measurements, therefore blurring the brightness temperature images.