Sub-Audio Magnetics (SAM): A High Resolution Geophysical Method for Simultaneously Mapping Electrical and Magnetic Properties of the Earth

Abstract

In recent times, there has been an accelerating trend in the exploration industry towards increased spatial resolution in geophysical surveys. Rapid development in computing technology and image processing techniques has meant that much finer detail is now being observed in the data and utilised, than was previously possible. However, geophysical surveys are often very labour-intensive and therefore, expensive. Consequently, there is a need to reduce the cost of acquiring high spatial resolution data. Developments in digital electronics have resulted in significant improvements in geophysical instrumentation. Magnetic surveys, in particular, have benefited from the advent of continuous sampling magnetometers which have made high spatial resolution or "High Definition Magnetics" (HDM) surveys both logistically and economically feasible. A review of other geophysical methods revealed that improvements in survey efficiency have not been achieved across all geophysical techniques. Higher precision data from the electrical techniques such as electrical resistivity (ER) and electrical induced polarisation EIP) have resulted from real-time signal processing enhancements. However, significant increases in survey efficiency were found to be restricted due to the logistical constraint imposed by the need for grounded electrodes. Similarly, improvements in survey efficiency for the electromagnetic techniques, such as, magnetometric resistivity (MMR), magnetic induced polarisation (MIP) and SIROTEM, are limited by the time-consuming requirement to precisely orientate and level the sensor prior to taking a reading.