Preliminary Results of Impacts of Ionospheric Scintillations on GAST-D Ground Integrity Monitors
Susumu Saito, Electronic Navigation Research Institute (ENRI), National Institute of Maritime, Port, and Aviation Technology (MPAT), Japan; Sabine Zureikat, ENRI, MPAT, Japan/Ecole Nationale de’l’Aviation Civile, France; Takayuki Yoshihara, ENRI, MPAT, Japan
Location: Grand Ballroom G
Date/Time: Wednesday, Jan. 31, 10:30 a.m.
GAST-D (GBAS Approach Service Type D) is a class of GBAS (Ground-based Augmentation System) based on a single-frequency signals of GNSS to support Category II/III approach and landing of aircraft. To satisfy the very high requirements for safety, integrity monitors are needed to be implemented. Among different threats to the integrity of GAST-D, ionospheric irregularities are one of the most serious ones. Especially, the low latitude ionosphere, where ionospheric disturbances frequently occur is a very challenging environment for GAST-D.
In this study, effects of ionospheric amplitude scintillations on integrity monitors of GAST-D were investigated based on the data obtained by an experimental prototype of a GAST-D ground subsystem installed at New Ishigaki Airport located in a low magnetic latitude region (24.3ºN, 124.2ºE, 19.6ºN magnetic) and scintillation data obtained near the GAST-D ground subsystem. Existence of plasma bubbles which are characteristic ionospheric disturbances in the low magnetic latitude region are monitored by an all-sky airglow imager located near the GAST-D ground subsystem.
Impacts of ionospheric amplitude scintillations on four integrity monitors, namely cycle-slip (CS), code-carrier divergence (CCD), ionospheric spatial gradient monitor (ISGM), and DSIGMA range domain monitors were discussed. Occurrence of cycle-slips increased with increasing S4 index values. At an S4 index of 1.0, the occurrence rate of cycle-slip was more than 50%. The CCD test statistics as well as a general test statistics of ISGM, which is the double-differences of carrier-phase (DD carrier-phase) also increased as the S4 index increases. On the cause of the positive correlation of the CCD test statistics and DD carrier-phases to the S4 index, more investigation is necessary. For the DSIGMA range domain monitor, methodologies of investigation are presented. Detailed analysis including impacts of the phase scintillation on the GAST-D integrity monitors is left for the next steps of this study.