Total Electron Content (TEC)
Total Electron Content (TEC) maps are being produced from dual-frequency GPS observations in the form of Spherical Cap Harmonic (SCH) coefficients over Canada and adjacent regions. Slant TEC estimates at Ionospheric Pierce Points (IPPs) on a single layer model are obtained from GPS interfrequency, phase-smoothed, geometry-free pseudorange measurements corrected for satellite and receiver differential code biases. These slant values are converted to the vertical (vTEC) using an empirical mapping function. The IPP coordinates are transformed to a spherical cap coordinate system centered over Canada. Using vTEC at all IPPs in this coordinate system, SCH coefficients are estimated and a regional TEC map is generated. The fitting is performed using a maximum degree-index of 4 for a spherical cap having an angular radius of 30° centered at 62° latitude and -90° longitude.
Two TEC mapping products are available: near-real-time and daily maps. Near-real-time TEC maps are generated every 15 minutes using data from about 40 high-rate (1 Hz) GPS stations using differential code biases estimated the previous day. Near-real-time maps are automatically generated and displayed online every 15 minutes based on all measurements within the 15 minute interval indicated. Previous maps can be viewed using the Total Electron Content (TEC) Archive. Daily maps are produced every 2 hours based on data from about 90 GPS stations tracking at 30 sec. Daily maps for a given day are calculated the following day so that the 24 hour observation file for that day can be used to estimate the satellite differential code biases. Daily maps for the previous days can be viewed using the Total Electron Content (TEC) Archive.
For further information on how space weather affects GPS positioning please visit the Space Weather effects on GPS page.
Ghoddousi-Fard, R., P. Heroux, D. Danskin, and D. Boteler (2011), Developing a GPS TEC mapping service over Canada, Space Weather, 9, S06D11, doi:10.1029/2010SW000621.
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