ALBERT

Description: Synthesis of natural electric and magnetic Time-series using Inter-station transfer functions and time-series from a Neighboring site (STIN) is a new approach for recovering natural electric and magnetic fields and reduce the influence of anthropogenic noise. The proposed approach modifies the windows of the local electric and magnetic time-series that are affected by noise with time series resulted from modifying the spectra of the magnetic time-series from a neighboring site with the inter-station transfer functions between the local and neighboring sites. The STIN method was tested with artificially contaminated electric and magnetic time-series. Comparison between STIN-corrected time-series and original non-contaminated time-series shows high similarity, both in the time and frequency domains. Differences were quantified using the normalized root-mean-square error, the correlation coefficient, and the signal to noise ratio. The STIN method was also applied to two sites affected by unconstrained anthropogenic noise, thus demonstrating the ability and accuracy of STIN in synthesizing natural electric and magnetic fields and reducing the influence of anthropogenic noise. The synthesized time-series provided by STIN show the method to be valuable for MT geophysical applications, by increasing the reliability when constrains the MT impedance tensor, and by reducing the scatter of data points when the time-series are affected by noise, particularly for longer periods. As STIN is based on inter-station transfer functions, the electric and magnetic time-series can be treated independently, enabling computation of the MT impedance tensor even when the electric and magnetic time-series of the local site were recorded at different times.

Description: The transient electromagnetic method (TEM) and controlled-source audio-frequency magnetotellurics method (CSAMT) are commonly used in detecting water abundance of rock formation and faults in coal mines. However, these methods show low accuracy, given the multiplicity of their inversion results, especially for areas with minor differences in lithology and electrical property. To improve the accuracy of electromagnetic exploration, a pseudo-2D joint inversion is performed. The objective function of this pseudo-2D joint inversion is established, and the joint inversion process is constrained by resistivity logging data. Afterward, the symmetric successive over-relaxation (SSOR) is used to realize the pseudo-2D joint inversion calculation of TEM and CSAMT with well log constraint. The effectiveness of joint inversion is verified by combining synthetic and field data. Results show that the pseudo-2D joint inversion results of TEM and CSAMT with well log constraint correspond to the actual geological situation. Compared with either TEM or CSAMT, joint inversion has a significantly better capability of reflecting water abundance in rock formation and faults.