Method and apparatus for measuring ellipse parameters of electromagnetic polarization in geophysical exploration

摘要

A method and apparatus for measuring ellipse parameters of polarization of an electromagnetic field are disclosed. When a geophysical anomaly exists which, in the presence of a primary alternating electromagnetic field will produce a secondary field, the resultant field is elliptically polarized and the ellipse of polarization is tilted at any location where the presence of the secondary field is being tested for. A receiver is provided having crossed coils, and both the receiver and transmitter have specific orientations which are set up whenever the receiver and transmitter are situated at any location for testing for the presence of an anomaly at least in the region of the receiver. When signals are detected on the crossed coils of the receiver, the receiver is maintained in its specific orientation while the signals from the crossed coils are examined at least so as to determine the phase difference quantity &phgr; between the signals from the crossed coils and the magnitude ratio quantity r of those signals. With the quantities &phgr; and r, such ellipse parameters of polarization of the resultant EM field in the region of the receiver as the tilt angle, ellipticity angle and ellipticity ratio thereof can be determined by mathematical analysis and processing. In high noise situations, or where the signal level on either receiver coil is low, signal level stacking circuits are utilized to arithmetically add signal levels of succeeding signals until such time as one of the signals being stacked reaches a predetermined level. In general, the transmitter and receiver may operate at a number of different frequencies, one at a time; and while they are not linked in any way, each of the transmitter and receiver contains identical stable oscillators and frequency dividers.