APPARATUS FOR GEOPHYSICAL EXPLORATION

摘要

Two vector components of the EM field, e.g., Hy and Ex, are picked up by suitable probes. The resulting signals are filtered by narrow band pass filters around a center frequency and amplified by gain selectable amplifiers to an acceptable level for a pre-processing circuit which enables fast mathematical operations to be done. The preprocessing circuit uses an all pass quadrature (90.degree.) phase shifter, four fast multipliers and four integrators under the control of a timing circuit. The output of the preprocessing circuit are converted to digital values to permit mathematical processing. Then, the ratio, the phase shift and the coefficient of coherence between the two vector components of the MT-EM field are calculated. The above operations can be repeated for various frequencies .omega.o. The coherence value gives an indication of the quality of the measurement. With a low coherence value, the measurement must be repeated because the noise is too high. A graph of the ratio and phase shift values of the EM field with respect to .omega.o enables a geophysicist to make an interpretation of deep rock conductivities at various depths.