Performance of GAST-D Ionospheric Gradient Monitor Studied with Low Latitude Ionospheric Disturbance Data Obtained in a Real Airport Environment

S. Saito, T. Yoshihara, H. Nakahara

Abstract:	Ionospheric delay gradient detection is one of the most important and difficult components of integrity monitors for GAST-D (GBAS Approach Service Type D) is a single-frequency based GNSS ground-based augmentation system (GBAS) that supports Category II/III approach and landing. Ionospheric spatial gradient monitor (ISGM) for GAST-D based on the single-frequency carrier-phase-based and code-aided (SP-CPCA) method is implemented and tested with the real airport environment at New Ishigaki Airport, Japan located in the low magnetic latitude region. Performance of ISGM under the nominal conditions is shown to be satisfactory. Some events of enhanced ISGM outputs, which may potentially cause false alarm of ISGM are observed. Dual-frequency analysis showed that they are unlikely to be ionospheric gradients. Monitoring camera images denied the possibility of transient multipath effects. It is concluded that they are likely to be tropospheric origin as observed in US and Europe. This study is the first to support the existence of sharp tropospheric delay gradient with dual-frequency measurements. The next step is to evaluate the ISGM performance under the ionospheric disturbed conditions identified by the scintillation and airglow measurements conducted near the New Ishigaki Airport.
Published in:	Proceedings of the ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	815 - 820
Cite this article:	Saito, S., Yoshihara, T., Nakahara, H., "Performance of GAST-D Ionospheric Gradient Monitor Studied with Low Latitude Ionospheric Disturbance Data Obtained in a Real Airport Environment," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 815-820.
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