Vertical electron content from ionograms in real time

A new technique for calculating the vertical total electron content (TEC) from ground‐based ionosonde measurements is introduced. The ionogram provides the information to directly calculate the vertical electron density profile up to the peak of the F 2 layer. The profile above the peak is approximated by an α‐Chapman function with a scale height that is derived from the profile shape around the F 2 peak. The ionosonde TEC, or ITEC, is then calculated as the integral from 0 to ∞ over the entire profile. ITEC values from Digisonde observations at Millstone Hill, Wallops Island, and Jicamarca are compared with incoherent scatter radar and with Faraday and TOPEX satellite TEC measurements, showing very good agreement at middle latitudes and the magnetic equator.