Discriminating Underground Nuclear Explosions and Earthquakes in GPS-detected Traveling Ionospheric Disturbances: Case Study

Jihye Park, Dorota A. Grejner-Brzezinska, R.R.B. von Frese, Y. Jade Morton

Abstract:	GNSS measurements can be used to determine the ionospheric delay along the paths of the signals. The ionosphere responds not only to the solar activity and space weather condition but also to earthquakes, tsunamis, tropical storms, chemical explosions, underground explosions, and other geophysical activities. These phenomena can generate disturbances in the ionosphere, referred to as traveling ionospheric disturbances (TIDs). Consequently, TID can be extracted from the ionospheric delay of GNSS signals byeliminating the dominant trend from the solar diurnal variation. The aim of this study is to discriminate the specific TID wave generated by the underground nuclear explosion from other events such as earthquakes. In this paper, the TIDs induced by an earthquake and underground nuclear explosion (UNE) are compared, and the unique characteristics of the waveforms created by these two types of events are demonstrated. To discriminate the waveforms of TID induced by UNEs from those generated by earthquakes, the North Korean UNEs, detonated in 2006 and 2009 were compared to the TIDs from the earthquake of 2011 that occurred in Tohoku, Japan. For each event, the GPS data from the permanently tracking stations that are located nearby the event were collected. The total electron content (TEC) was computed from the ionospheric delay extracted from the dual frequency GPS signals. The small fluctuations in the regional trend of the TEC, caused by the specific local events, were extracted by taking numerical third order horizontal 3-point derivatives. The TID waveforms were identified by the significant derivative peaks. Moreover, the TIDs detected by multiple stations with varying distances from the event were used to determine the coordinates of the epicenter of the event. This study is focused on exploring the characteristics of the TID waveforms. The TIDs detected by the 3-point derivatives of the TEC signal were independently verified by a wavelet denoising technique. The correlation coefficients (CC) between the TID signals of the UNEs of 2009 and 2006 were significantly higher than their CCs with the TIDs from the Japanese earthquake. In addition, the related power spectra revealed that the TID waveforms from the earthquake had significantly lower frequency components than the UNE-induced TIDs. The results of this case study indicate that TIDs induced by different events can be readily discriminated based on the distinctive spectral properties of the waveforms.
Published in:	Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012) September 17 - 21, 2012 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	2682 - 2691
Cite this article:	Park, Jihye, Grejner-Brzezinska, Dorota A., von Frese, R.R.B., Morton, Y. Jade, "Discriminating Underground Nuclear Explosions and Earthquakes in GPS-detected Traveling Ionospheric Disturbances: Case Study," Proceedings of the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2012), Nashville, TN, September 2012, pp. 2682-2691.
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