One of major challenges facing Earth's science in the next decade and beyondis the development of an accurate long term observational data set to study global change. To accomplish this, a wide range of observations will be required to provide both new measurements, not previously achievable and measurements with a greater degreee of accuracy and resolution than the ones which are presently and currently available. Among the parameters that are currently retrieved from satellite vertical sounding observations, temperature and moisture profiles are the most important for the description of the thermodynamic state of the medium. Other parameters, like those describing the cloud fields, the surface state