Global Ionospheric Specifications Using the Global GPS Network
A capability of monitoring the global distribution of ionospheric
total electron content (TEC) has been developed at JPL using
dual-frequency observations from a
worldwide network of Global Positioning
System (GPS). Using the GPS data Combined with the Kalman filter
technique and an ionospheric model, global ionosphere maps
(GIM) of vertical TEC can be produced
with an hourly or sub-hourly resolution.
Validation of GIM and Calibration for Single-Frequency Altimetry Missions

The accuracy of the GIM solutions
can be assessed by direct comparisons with independent vertical
TEC measurements, such as those retrieved from the dual-frequency
altimetry data taken by the TOPEX satellite.
On the other hand, single-frequency satellite altimetry missions
will benefit from using GIM solutions
to provide global ionospheric corrections.