Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa43b1754g&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SA43B-1754
Physics
[2427] Ionosphere / Ionosphere/Atmosphere Interactions, [2435] Ionosphere / Ionospheric Disturbances, [2494] Ionosphere / Instruments And Techniques, [7294] Seismology / Seismic Instruments And Networks
Scientific paper
Ionospheric disturbances can be observed as small variations in the Integrated Electron Content (TEC), which are measurable through phase advance in trans-ionospheric Global Navigation Satellite System (GNSS) signals. Large GPS networks, in Southern California and Japan, provide many, spatially dense, samples of the IEC time series, which can be cross-correlated to detect the coherent structure of these disturbances. The propagation delay between any pair of stations can also be obtained from the cross-correlation and used to estimate the propagation speed and direction. In this presentation, we will apply wavelet processing to isolate coherent structure in the TEC time series, prior to the cross-correlation test of detection. Regions in the time-frequency space that show large values are identified and used to set the bandwidth of a filter-bank. After applying this filter bank to the TEC data, the filter band passing the largest power is selected, and then used to produce the filtered TEC time series. Pairs of filtered time series are then cross-correlated, as described above. This method is demonstrated on data from 1235 stations in the Japanese GEONET GPS network, separated into 32 smaller regional groups of around 40 stations each. Several smaller sub-networks enables changes in the disturbance to be studied, as well as geo-locating of potential sources from differences in the propagation direction and detection time. GEONET data are processed in a five-day window surrounding two underground nuclear tests conducted by North Korea on 25 May 2009 and 9 October 2006. We are presently studying disturbances that were observed on the day of the underground test and investigating the consistency of the propagation geometry to determine if these observed features are, in fact, the result of an atmospheric disturbance caused by the test, or an unrelated effect.
Garrison James L.
Lee Sang-Gak
Yang Yadong
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