Improved method for the estimation of the ionospheric irregularities by site dependent total electron content (TEC) amplitude fluctuation index

The scintillation effects are known to degrade the tracking performance of a GPS receiver. Possible Doppler shift observed on the GPS signal due to rapid phase variations could extend the bandwidth exceedingly, forcing the phase locked loop to its tracking limits, and the lost of signal can be observed especially at the frequency L2. For this, accurate estimation of the ionospheric irregularities is often not possible since ionosphere is usually assumed to be locally isotropic. In this study, short time (15 min.) amplitude fluctuation index (f/sub a/) that is function of time, orbit number and satellite number, and hourly amplitude fluctuation index (F/sub a/) that function of hour and orbit number only, are defined. f/sub a/ can be calculated at any point on the surface of the Earth for each 15 minute long time section using only one satellite, and F/sub a/ can be calculated hourly and using satellites in the vicinity of the receiver. It is shown that utilizing the amplitude fluctuation indices f/sub a/ and F/sub a/, oblique examination of the index is possible, without assuming a perfect vertical path. Finally, the variations on the total electron content corresponding to different cases are discussed on numerical results.