Tropospheric error modeling for high integrity airborne GNSS navigation

This paper surveys Global Navigation Satellite System (GNSS) tropospheric modeling techniques currently employed in Space Based Augmentation Systems (SBAS), Ground Based Augmentation Systems (GBAS), and in precise point positioning applications. A method for generating GBAS tropospheric corrections without the use of meteorological sensors is discussed using seasonal models like those used in SBAS. An approach on how residual tropospheric errors can be handled in high-accuracy/high-precision carrier phase differential position applications is described. Current approaches for over-bounding residual tropospheric errors in GBAS and SBAS applications ignore correlation of these errors between satellites. This is not an issue today as residual tropospheric errors can safely be assumed to be small compared to other residual error components. However, with improvements in these other measurement errors associated with GNSS modernization, this assumption may no longer be appropriate. The types of integrity monitoring envisioned by the GNSS Evolutionary Architecture Study (GEAS) may benefit from a reexamination of the treatment of tropospheric errors as described here.