METHOD AND APPARATUS FOR DETERMINING THE ELECTRICAL RESISTIVITY OF THE SUBSOIL BY ELECTROMAGNETIC SURFACE WAVES

摘要

1365381 Prospecting COMPAGNIE D'APPLICATIONS ET DE DIFFUSION DE TECHNIQUES NOUVELLES SarL 17 Aug 1971 [5 Oct 1970] 38498/71 Heading G1N The method of measuring sub-soil resistivity by transmitting an electromagnetic wave from a remote point to the point at which the sub-soil resistivity is to be determined, is characterized in that the received signal 1, Fig. 1 after amplification 2 and filtering 4 is multiplied 6 by a reference signal 8 of the same frequency as the transmitted signal and the phase of the reference signal is adjusted to maximize the output of the multiplier which is passed to a measuring circuit. The reference signal generator can be linked to the transmitter at the remote point, but if the distance is too great it is adequate to control both the transmitter and the reference signal generator by matched crystal oscillators. The received signal may be recorded on magnetic tape before being replayed (possibly at a higher speed) to the processing circuit.