As the EUMETSAT Polar System-Second Generation (EPS-SG) is being prepared, a new generation of the IASI instrument has been designed. The IASI New Generation (IASI-NG) will measure at spectral resolution and a signal-to-noise ratio improved by a factor 2 compared to its predecessor. Measurement precision will be improved as well. The high amount of data resulting from IASI-NG will present many challenges in the areas of data transmission, storage and assimilation and the number of individual pieces of information will be not exploitable in an operational Numerical Weather Predictions (NWP) context. For these reasons, an appropriate IASI-NG channel selection is going to be performed aiming to select the most informative channels for NWP. In this paper the propaedeutic study towards a channel selection is displayed. More in details, the construction of a simulated observation database, to be used as a basis for selection, and the use of a diagnostic method to build a full covariance matrix of the observation errors (R matrix), will be here described.