Dual Mode Operation of GEM-3 as TD/FD Sensor
Abstract
Electromagnetic geophysical exploration tools come in two types, frequency domain and time domain. A frequency-domain system utilizes continuous sinusoidal signals at one or more discrete frequencies, and the measurement consists of amplitude and phase (or realliuphase and imaginary quadrature) response at each frequency; a time domain system utilizes abrupt step or pulse signals, and the measurement consists of time-sampled transient responses. Historically, each has shown to be effective, but each with various claims of advantages over the other. In principle, time domain and frequency domain should provide equivalent information and one type of response to a target could be derived from the other. Complete equivalence can be shown for the ideal systems having infinite bandwidth/time interval and sample rate, and no noise. For real systems, it is not obvious how equivalent they are - i.e., does a particular flmedomain system provide some information not easily attained with a particular frequency-domain system and vice versa? Are there real advantages of each over the other? Until recently, technology constraints precluded building a sensor that could operate in both modes as effectively as a modeqailored system, so no one ever did. Frequency-domain systems usually employed tuned high-Q resonant circuits to efficiently concentrate energy at the desired discrete frequencies, changing frequencies required switching the tuning circuit, and each frequency was operated one at a time. Th%e-domain systems employed a charge/discharge circuit not readily operated in a continuous-wave mode.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 28, 2004
- Accession Number
- ADA481014
Entities
People
- Bill Sanfilipo
- Haoping Huang
- I. J. Won
- Mike Shipman