Small-scale ionospheric delay variation associated with plasma bubbles studied with GNSS and optical measurements and its impact on GBAS

摘要

For differential GNSS systems such as the ground-basedaugmentation system (GBAS), spatial variation (or spatialgradient) in ionospheric delay is a critical issue.In the low latitude region, the dominantionospheric disturbance is the plasma bubble. Plasmabubbles are local ionospheric depletions that often occurafter sunset. They accompany ionospheric irregularitieswith various scale sizes from 100 km down to a meter.However, the characteristics of the low latitudeionospheric variations in terms of a specific threat toGBAS have not been well studied yet.This paper studies the spatial relationshipbetween the ionospheric delay gradients and the largescaleplasma bubble structure. The ionospheric delaygradients are measured with spaced receivers at Ishigaki,Japan. Large-scale plasma bubble structures are measuredwith an all-sky airglow images observed at Yonaguni,Japan.The ionospheric delay gradients are shown tohave large values at the edges of plasma bubbles, andtheeir directions are consistent with the direction of theelectron density gradient inferred from the airglow imagesas well as the expectation that the gradient.In some cases, however, the ionospheric delaygradients have large values had large values at locationsother than the plasma bubble edges. The absoluteionospheric delay with dual-frequency measurements andthe drift velocity will be analyzed to investigate the scalesize and the amplitude of the irregularities that cause theionospheric delay gradients. Co-site observations of theionospheric delay gradient and the airglow at Ishigaki tohave nearly common line of sights for both themeasurements.