Absolute Ionosphere Slant Delays From Ambiguous Carrier Phase Data

A new method for computing absolute (unambiguous) levels of Total Electron Content (TEC) in the ionosphere and subsequently the L1 and L2 phase advances of GPS is presented, dubbed “ICON” (for its primary purpose of modeling the Ionosphere over CONus). Unlike previous computational methods, this method relies solely upon dual-frequency, ambiguous carrier phase data with no reliance on pseudo-range, a-priori values or other external information. The only requirements for this method are that mapping functions between sufficiently close slantviews of the ionosphere are available, and that the GPS data come from a network of ground stations, geographically separated so as to allow satellites to be viewed by a variety of stations at overlapping times. This method can be applied either through independent least squares adjustments (such as one day of data at a time), or may be applied in an on-the-fly mode, where new data are adjusted into pre-adjusted values epoch-by-epoch. Sensitivity analyses are presented, showing both the advantages and current limitations of this method. Additionally, comparisons between ICON and the IGTEC and MAGIC models of the ionosphere are presented and discussed. Plans to improve the method, as well as its application toward forecasting of the ionosphere are also included.