A Preliminary Study of the Effect of Ionospheric Scintillation on WAAS User Availability in Equatorial Regions

摘要: While Wide Area Augmentation System (WAAS) user performance is expected meet aviation requirements under most conditions, infrequent ionospheric anomalies may result in significant degradation at certain times and locations. Scintillation, caused by local ionospheric plasma anomalies that intercept the path of GPS signals, can cause severe signal fades and phase vacillations that may lead to loss lock or increased measurement errors. The degree which scintillation will affect user availability not well known, however, detailed models phenomena are limited the sparse amount data available. To evaluate threat may pose to WAAS users, existing models have been adapted provide probability distributions for signal amplitude variations. Samples from these distributions fed into a simplified receiver simulation that outputs losing given a specified nominal signal-to-noise ratio. These results are integrated with an WAAS Service Volume Model (SVM) assess resulting user availability for an example network covering South America. The indicate susceptible locations, moderate high of loss-of-lock low-elevation satellites, strong scintillation does same higher-elevation satellites. The problem particularly bad codeless L2 tracking used networks generate ionosphere measurements. However, when compared case of large ionosphere delays without scintillation, precision approach much worse because these periods higher errors thus signifi-cantly diminished relative nominal ionosphere conditions. Non-precision applications retain even under scintillation. Better assessments effect on WAAS will be possible once upcoming solar peak in 2000-01 delivered National Satellite Testbed (NSTB) Phase 1 reference stations.