| 摘要 |
<p>A frequency domain geophysical electromagnetic surveying system is provided in which intermittent primary fields having sharp terminations are generated in a cycle having a fundamental frequency by a transmitter (8), and a receiver (14) includes a gate (22) passing only secondary signals received during interruptions of the primary field, the gated signal being applied to filters (24, 25) turned to harmonics of the predetermined frequency. The filter outputs are synchronously demodulated (261, 26Q, 281, 28Q) to provide signals corresponding to at least the in-phase component of the secondary signal at the fundamental frequency, and preferably in-phase and quadrature components at at least two harmonics. The system can provide improved resolution particularly of the characteristics of inphase secondary signals received from terrain being surveyed.</p> |
