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In a GBAS...
  • A
    The L2 frequency is used, and compared to the data received from the L1 frequency, to reduce the ionospheric error.
  • B
    A pseudolite is positioned close to the runway, transmitting information about the ionospheric and tropospheric errors to nearby aircraft.
  • C
    An extra satellite is used to verify the integrity of the signals from the other satellites.
  • D
    Information about the ionosphere is up-linked to a geostationary satellite, which distributes the information to properly equipped receivers.

A Ground Based Augmentation System (GBAS) augments the existing Global Positioning System (GPS) used in U.S. airspace by providing corrections to aircraft in the vicinity of an airport in order to improve the accuracy of, and provide integrity for, these aircrafts' GPS navigational position.

Pseudolites are ground-based transmitters that send global navigation satellite system like signals. These are positioned close to the runway and when the aircraft is close, the ionospheric and tropospheric transmission paths will be virtually identical so these errors are effectively eliminated.

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