| Ionospheric correction using tomography (1997) | |||||||||||||||
Abstract | |||||||||||||||
| The most demanding application of wide area di erential corrections to GPS is vertical positioning of aircraft on precision approach. Here the Wide Area Augmentation System (WAAS) combines accuracy requirements on the order of ones of meters with safety of life integrity requirements which specify that any vertical position errors greater than the Vertical Protection Limit be enunciated to the ight crew within six seconds. The ionosphere is the foremost impediment to satisfying these requirements. Stanford, as a member of the National Satellite Test Bed (NSTB), is developing techniques for estimating the ionosphere in real-time. Previous research has established a connection between ionospheric error and vertical positioning error within the framework of modal decomposition. Ionospheric tomography isa natural extension of modal decomposition to the estimation of the ionosphere's three-dimensional electron density. We present a tomographic estimation algorithm and its implementation over the NSTB network. This estimator supplies not only corrections to the user but also appropriate con dence information for predicting the accuracy of those corrections in the aircraft. The tomographic approach to ionospheric correction obviates the troublesome obliquity factor associated with typical gridded vertical delay algorithms. The capability of ionospheric tomography is demonstrated by a time series of 3D electron density reconstructions over the Coterminous United States (CONUS). The accuracy, integrity, and availability afforded the user by this approach is quanti ed through application on live NSTB observations. | |||||||||||||||
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