The Final Project has been developed in the framework of the ESA’s Soil Moisture and Ocean Salinity (SMOS) mission [1], during the development of Pre-Commissioning and Commissioning phases. The first steps of this work were in September 2009 with the Remote Sensing Laboratory group of TSC (Theory of Signal and Communications Department) at UPC [2]. One of the main objectives of any mission is to obtain and provide stable and accurate final products. So, a well-calibrated instrument provides the basis for stable and accurate measurements. The calibration of any Earth Observation sensor is a key stage which encompasses those tasks which are necessary to convert the raw measurement data into science data. The characterization of the instrument is a requirement for the development of the calibration activities. Characterization consists of the measurement of the typical behavior of instrument performances, including subsystems, which may affect the accuracy or quality of its response or derived data. The aim of this Final Project is to perform a comprehensive temperature sensitivity analysis of the instrument that is the SMOS payload. To do this, it is necessary to characterize the Power Measurement System (PMS) included in each receiver over the physical temperature. Additionally, the correlation phase related to the Local Oscillator (LO) located in each segment of the instrument is also analyzed. PMS calibration parameters (gain and offset) and the correlation phase (LO phase) are planned to be periodically updated during the mission to account for possible instrumental drifts. These parameters are tracked, initially on-ground and after in orbit, during the measurement mode using their respective corrections to remove physical temperature drifts.