Impact of atmospheric water vapor on the design of a Ku band geosynchronous SAR system

We consider a geosynchronous Ku band system, and the defocusing effects due to the temporal and spatial variability of the atmospheric water vapor. Due to the very slow formation of the spatial chirp (minutes or even hours), the temporal change of the local water vapor content could be significant, thus preventing a correct image focusing and the formation of a coherent image. Using GPS and ground based radar data, we estimate and model the spatial temporal correlation function of the water vapor delay. Then, for a given spatial scale, we estimate the maximum time within which the temporal evolution of the water vapor should be carried out, to be able to track its temporal evolution. This requisite constrains both the EIRP and the apparent velocity of the satellite. Then, we evaluate the possibilities of real time ground motion analyses, as a function of the spatial and temporal resolution and the EIRP.