Scintillations are rapid fluctuations of the phase and amplitude of satellite radio signals travelling through the ionosphere, caused by time varying electron density irregularities. Scintillations can have a considerable effect on the performance (e.g. Positioning Quality) of Global Satellite Navigation Systems (GNSS) as they may reduce the accuracy of the pseudo range and phase measurements and can even cause a loss of lock on the signal. The paper will discuss some tools which are under development to monitor the occurrence of scintillation and to assess the impact on the final positioning quality through Fugro's worldwide network of GNSS stations and a network of stations operated by the University of Nottingham.