An application of complex demodulation technique to geomagnetic data and conductivity anomaly studies |
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| Authors: | A K Agarwal B P Singh N Nityananda |
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| Institution: | (1) Indian Institute of Geomagnetism, 400005 Bombay |
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| Abstract: | The method of complex demodulation has been used here to compute the amplitude and phase of a signal present in a geomagnetic
series using, Banks’ method. It is found that the results are quite accurate when four or more continuous cycles of the signal
of interest are present. The same limitations have also been observed when band-pass filters are used to isolate a signal.
The information on phase is always correct. It is concluded that complex demodulation will give correct results for periodic
variations like 11-year, 27-day, Sq or pulsations; but will give small values of amplitude for signals like sudden impulses
or bays. The latter is not a limitation in conductivity studies where ratios likeZ/H, Z/D orH/D are mostly used in calculations. It has been shown that even with the records of one magnetic storm the cause of anomalies
can be accurately identified which otherwise would need a large number of events. |
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| Keywords: | Time series analysis complex demodulation geomagnetic deep sounding conductivity anomalies |
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