Scale Model Studies of a Transient Electromagnetic Prospecting System Using an Interactive Minicomputer
Scale models have been used for over thirty years in studying the electrical and electromagnetic techniques of geophysical prospecting, and are particularly useful when mathematical or numerical methods are unreasonably difficult. A model study facility has been set up at Macquarie University, Sydney, Australia, to study the transient electromagnetic method of geophysical prospecting. The basic unit in the facility consists of a 35Kword INTERDATA minicomputer which controls the timing and waveform of the transmitted pulse as well as subsequent data collection and processing. A wide-band amplifiler provides an interface between the computer and the small multiturn loops used for model studies. Input and output data are fed via the computer to a teletypewriter. The use of an interactive technique between the computer and operator enables optimum timing and amplifier settings to be easily determined for each model. A model of a uniformly conductive half-space was used to validate the experimental arrangement, and excellent agreement was found between theoretical and model results. A model study of an orebody enabled estimates of bulk conductivity to be made.
Numerical and analogue modelling of induction effects in laterally non-uniform conductors
Modelling of electromagnetic fields in laterally non-uniform geoelectric structures is briefly reviewed. Attention is paid to progress achieved specifically during the last three years in numerical and analogue techniques of solving two- and three-dimensional problems. Some new important results are also mentioned.
Computer Modelling of Electrical Conductivity Structures
The study of the Earth by means of its natural clcctromagnetic field has received a stimulus with the development of numerical solutions of Maxwell's equations for two-dimensional conductivity structures (Madden & Swift 1969; Wright 1970). In particular, Jones & Pascoe (1971) and Pascoe & Jones (1972) have published general computer programs which have received widespread application. It is the purpose of this note to reveal and discuss an error in their mathematical derivation. The Taylor's Series expansions illustrated on p. 7 of Jones & Pascoe (1971) can be solved for ( d f f l ~ 3 y ~ ) ~ and (d2fdz2), by Cramer's Rule or by algebraic manipulation. Substitution into their equation (10) yields