Underground nuclear explosions (UNEs) can induce acoustic-gravity waves,which disturb the ionosphere and initiate traveling ionospheric disturbances(TIDs). In this paper, we employ a multi-step and multi-order numericaldifference method with dual-frequency GPS data to detect ionosphericdisturbances triggered by the North Korean UNE on 25 May 2009. SeveralInternational GNSS Service (IGS) stations with different distances (400 to1200 km) from the epicenter were chosen for the experiment. The results showthat there are two types of disturbances in the ionospheric disturbanceseries: high-frequency TIDs with periods of approximately 1 to 2 min andlow-frequency waves with period spectrums of 2 to 5 min. The observed TIDsare situated around the epicenter of the UNE, and show similar features,indicating the origin of the observed disturbances is the UNE event.According to the amplitudes, periods and average propagation velocities, thehigh-frequency and low-frequency TIDs can be attributed to the acoustic wavesin the lower ionosphere and higher ionosphere, respectively.
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