Sub-Daily Northern Hemisphere Ionospheric Maps Using the IGS GPS Network

Ionospheric total electron content (TEC) data derived from dual-frequency GPS signals from 30 globally distributed IGS network sites are fit to a simple ionospheric shell model, yielding, simultaneously, values for the satellite and receiver biases, and a map of the ionosphere in the northern hemisphere every 12 hours during the period of Jan. 1-15, 1993. RMS residuals of 2-3 TEC units are observed over the 20-80 degree latitude band. Various systematic errors affecting the TEC estimates are discussed. The capability of using these global maps to produce ionosphere calibrations for sites at which no GPS data are available is investigated.