TEMConfigurator, a new transient electromagnetic forward modelling interface, and evaluation of AgTEM-Wallaby and AgTEM-Wallaroo towed Transient Electromagnetic Systems capabilities and limitations.

Towed transient electromagnetic systems Wallaby and Wallaroo, operated with AgTEM and TerraTEM electronics have been in development and use in Australian agricultural and mining applications since 2002. During development, many variations of towed transient electromagnetic survey have been attempted demonstrating that design must be limited within a small range of each of the relevant design parameters. One cannot, for instance, expect deeper penetration just from infinitely increasing any parameter. All parameters make a difference, but are optimal only in small ranges, and most must be measured and stabilized accurately. Forward modelling involving variation of all parameters is invaluable for recognising and teaching system limitations. Forward modelling to generate sets of type curves provides a means of fully understanding capability and practicality of different towed TEM systems. New software, `TEMConfigurator', developed by the principal author, facilitates generation of sets of type curves comparing any configuration over a range of earth models. It is an interactive graphical wrapper for only the time domain electromagnetic forward modelling capabilities of the program `AarhusInv' of the Aarhus Hydrogeophysics Group. For towed TEM systems, tests at sites of known geology have demonstrated that subtraction of forward modelled data from field data collected at a site of known response is essential for determining system response and for realising the full capability. In-loop receivers detect the deep signal just as effectively as receivers out of the transmitter loop however accurate modelling of such signal is more difficult for in-loop receivers and must be balanced with consideration of logistical pragmatics. The contrast between slightly different forward models should be evaluated to determine detectability of predicted features of interest in the ground prior to attempting any survey. TEMConfigurator facilitates such detectability prediction.