Space Based Communications

The presence of free electrons in the ionosphere modifies the propagation of radio waves. To the first order, the effect on range measurements (radar altimeters) is proportional to the total number of electrons (TEC) along the ray path and inversely proportional to to the square of the frequency of the radio wave.

The TOPEX/Poseidon mission was launched in 1992 and is a joint project between CNES and NASA. It is equipped with a dual-frequency radar. Using both frequencies and the known dispersion curve, the instrument is able to calculate its own ionospheric correction. Welcome to AVISO/Altimetry (CNES, Toulouse, France), where information about the TOPEX/Poseiden mission - "how it works" can be found.
Also see the JPL/NASA TOPEX/Poseidon site.

• GPS derived TEC (A TEC Processing Primer)
• The CODE/AIUB Ionosphere Page
• GPS Strategies
• How TOPEX/Poseidon Works

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