Chapter 14 - Signal Discrimination of External Geomagnetic Effects Using the Transfer Function Approach with Continuous Wavelet Transform

Abstract

External-source geomagnetic variations in the ULF band (f<10Hz), including geomagnetic pulsations and storms, may create noise in controlled-source electromagnetic explorations. Periodic and/or irregular noise affects the accuracy of transfer function estimation. The authors have developed an effective algorithm to reduce the geomagnetic effects in observed magnetic and electric field data on the ground. This method is called the interstation transfer-function (ISTF) method, and it is based on magnetotelluric and remote reference techniques. In this method, a continuous wavelet transform is applied instead of the conventional Fourier transform in all of the processes of data analysis. The proposed method was applied to the electric and magnetic field data obtained in Boso Peninsula, Japan. Magnetic data from Kakioka Magnetic Observatory, Japan Meteorological Agency, were used as the remote reference. The accuracy of the estimated interstation transfer functions was quite high and contributed to the appropriate reduction of effects from external sources. The validity of the signal reconstruction was also examined by using simulated signals. The proposed method has a high ability to eliminate external source fields.