SYSTEM AND METHOD FOR EARTH PROBING WITH DEEP SUBSURFACE PENETRATION USING LOW FREQUENCY ELECTROMAGNETIC SIGNALS

摘要

An earth probing system uses deep penetration of electromagnetic waves into soil and other media. Advantage is taken of lower attenuation of radar waves in soil by frequencies of about three megahertz or less. Bursts of electromagnetic energy of various frequencies in this range are consecutively transmitted. The transmitting antenna (118) is continuously tuned, so as to maintain resonance during each burst, allowing large circulating currents and high power output. In a receiving antenna system, a dual antenna arrangement (111, 112) is providing for obtaining improved reception. A corresponding dual antenna circuit employs "spatial notch filtering", automatic adjustment of antenna gain-frequency variations, as well as compensation for transmitter gain variation. The system may be implemented in a totally analog, totally digital, or hybrid manner. Preferably, a signal processing method detects and digitally samples signals reflected from subsurface layers and buried objects (316, 316'). The invention provides means for removing system distortions and interfering signals, for compensating for aliasing errors and frequency-dependent antenna gain and phase variations, and for avoiding masking errors introduced by strong reflections.