No abstract

An interactive modeling and analysis program with a user-friendly graphical interface, for students and professionals in the field of exploration geophysics, has been developed. The ElectroMagnetic Modeling and Analysis program-EMMA-is capable of modeling one-dimensional responses for most electrical and electromagnetic methods and array configurations, including the time-domain, frequency-domain, resistivity, magnetotelluric and borehole methods. EMMA is available on-line, at no charge, from http://www.hgg.au.dk.An innovation of EMMA is the calculation of the model sensitivity analysis, a feature that is usually only present in inversion codes. The variance of the model parameters depends on the variance of the measured data and the way in which an error is mapped from the data to the model parameters. The measurement situation is realized by ascribing data noise to the model response. This facilitates the calculation of a realistic model parameter analysis. For time-domain data, piecewise linear waveforms, ramps and low-pass filters are included in the forward modeling scheme.When implemented on a multi-user relational database structure, EMMA is suitable for classroom exercises where the computers are connected through a local network. As an illustration and for motivation, three exercises focusing on the time-domain electromagnetic method are presented: the mapping of noise to model resolution; the effect of filters on the early time response and layer resolution; and an examination of the electric and magnetic field intensity to understand the physical mechanisms of the method.Short courses on the subject of the transient electromagnetic and resistivity methods for hydrogeophysical investigations, offered to technical advisers and to technical policy-makers, have demonstrated EMMA's succes in providing a productive learning environment.