Ionospheric monitoring by the Global Navigation Satellite System (GNSS).

摘要

The ionosphere reacts to geophysical events, such as earthquakes, tsunamis, surface explosions, underground nuclear explosions (UNE), etc. The Global Navigation Satellite System (GNSS) remote sensing (RS) enables monitoring of the ionospheric disturbances excited by these events. The purpose of this dissertation is to use GNSS RS to detect, discriminate, model and monitor ionospheric disturbances induced by earthquakes and UNEs.;Ionospheric delay, which can be derived from dual frequency GNSS signals, is converted to the total electron contents (TEC) along the signal path. After eliminating the main trend of TEC by taking the numerical third order horizontal 3-point derivatives, the traveling ionospheric disturbances (TIDs) are isolated. Since a TID can be generated due to various events, the source of TID must be verified. In this dissertation, the characteristics of the TID waves induced by an earthquake and an UNE are examined. The case studies are: (1) M9.0 2011 Tohoku, Japan earthquake, (2) 2006 North Korean UNE, and (3) 2009 North Korean UNE. From these experiments, the TIDs resulting from different types of events were characterized and discriminated due to the different waveform properties.;In addition, the epicenter of the point source can be determined by TID observations. In experiment (2), the 2009 North Korean UNE was examined, using data from eleven nearby GNSS stations. Within a few hours from the explosion, the GNSS stations detected the TIDs, whose arrival time for each station formulated the linear model with respect to the distance to the station. TIDs were observed to propagate with speeds of roughly 150 - 400 m/s at stations about 365 km to 1330 km from the explosion site. Considering the wind effect, the wind-adjusted TIDs located the UNE to within about 2.7 km of its seismically determined epicenter.;Through the case studies, the distinctive signatures of different events were demonstrated, which suggests the uniqueness of TIDs excited by different types of events. The major contributions of this dissertation is a demonstration of the applicability of GNSS RS to detect and discriminate geophysical events causing TIDs, and its ability to determine the epicenter of the point source.