Calculation of total electron content in ionosphere

Abstract

Total electron content (TEC) measurements have become more common since the introduction of modern global dual-frequency Global Positioning System (GPS) networks. The largest data set available to ionospheric scientists comes from slant paths connecting GPS receivers and satellites at 22,000 km. The TEC can be calculated using the GPS Toolkit based on the time and phase delay of the GPS signal, but there will be an unknown bias. Furthermore, the electron content can be measured using UHF/VHF radio beacons on board low-Earth-orbiting satellites. The TEC measurements, on the other hand, are obtained by combining TEC differences between slant paths, but they also contain biases. The Global Positioning System has 31 satellites in six orbital planes, each with a 55-degree inclination (Spilker, 1996). At any one time, every place on Earth will view around 8–10 satellites, or 1/3 of the constellation's total number of satellites. Each satellite has a 12-hour sidereal cycle and spends around 8 hours in the field of vision of a terrestrial receiver (usually 160). The typical information rate is 33.3 MHz, corresponding to a 0.167-degree angular difference between consecutive slant pathways.