MSAS stands for MTSAT Satellite-based Augmentation System. Like WAAS in North America, MSAS is an enhancement to GPS in Japan & Eastern Asia that can allow specially equipped GPS receivers to more accurately calculate their position.
MSAS will use a network of ground-based stations that compare their precisely known location with locations calculated from GPS satellite signals. Any differences found can be used to create correction data that's broadcast from MSAS satellites.
MSAS can help correct for error caused by distortion of GPS signals as they pass through the ionosphere as well as clock and orbital variations associated with individual GPS satellites.
Similar WADGPS systems that cover other parts of the world include WAAS (North America) and EGNOS (Europe).
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