This work presents a study on the enhancement of Numerical Weather Prediction (NWP) model simulations when assimilating SAR interferometry (InSAR) Precipitable Waver Vapor (PWV). A 3dVar assimilation scheme is used to assimilate InSAR data. The rotationally invariant spectrum of PWV maps obtained by GNSS, InSAR, and the NWP model is computed before and after the 3dVar assimilation. The average distance of GNSS stations in this region is about 100 km. The spatial resolution of NWP model simulations is 3 km. The spectra analysis shows that there are two cut frequencies, at 10-5 m-1 ÷ 2.10-5 m-1 and at 2.10-4 m-1 ÷ 3.10-4 m-1. The lower and higher cut frequencies seem to be related to the average distance of GNSS stations and the spatial resolution of NWP simulations.