A K Agarwal
Articles written in Journal of Earth System Science
Volume 89 Issue 1 March 1980 pp 67-77
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 like
Volume 95 Issue 3 November 1986 pp 373-380
Short-period events such as bays and storm sudden commencements (SSCs) have been analysed to investigate the nature of induced magnetic variations at two Indian magnetic observatories: Shillong and Gulmarg. It seems that near Gulmarg there is obvious connection between the induced magnetic variations and the two large scale features; the main central thrust (MCT) and the main boundary fault (MBF) in the north-west direction. The Dauki fault, an approximately east-west conductor, seems to be responsible for the conductivity anomalies at SHL.
Volume 99 Issue 4 December 1990 pp 681-692
The nature of horizontal anomalies and anomalous current systems in the region of the southern Indian peninsula is theoretically calculated with the aid of a thin sheet algorithm for northward and westward polarizations of a uniform inducing magnetic Held of period 20 min. The numerical model of the geoelectric structure is the one devised by Agarwal and Weaver (1989). The model results indicate the correspondence between the general features of the computed horizontal anomalies and the observed anomalies both at temporary array stations and at two permanent magnetic observatories (ANN and TRD). On the basis of model estimates of apparent resistivity and phase it is suggested that a one-dimensional interpretation of the sub-surface conductivity structure is valid near two of the array stations, whereas at all other coastal and inland stations, two-or three-dimensional interpretations of magnetotelluric (MT) data are required.
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