MTSAT Satellite Augmentation System (MSAS) is a Japanese SBAS (Satellite Based Augmentation System), i.e. a satellite navigation system which supports differential GPS (DGPS) designed to supplement the GPS system by reporting (then improving) on the reliability and accuracy of those signals. Tests have been accomplished successfully, MSAS for aviation use was commissioned on September 27, 2007.
A similar service is provided in North America by Wide Area Augmentation System (WAAS), and in Europe by European Geostationary Navigation Overlay Service (EGNOS).
Through the use of these Augmentation Systems an individual GPS receiver is able to correct its own position, offering a much greater accuracy. Typically GPS signal accuracy is improved from some 20 meters to approximately 1.5–2 meters in both the horizontal and vertical dimensions.