A High Stability Fluxgate Magnetic Gradiometer For Shallow Geophysical Survey Applications

The detection of induced and remanent magnetization of subsurface features provides a rapid survey technique. Rejection of the unwanted geomagnetic field and its diurnal variations is accomplished by adopting a gradient magnetometer arrangement in which only the difference signal from two magnetometers, separated by a short distance, is recorded. Nuclear resonance scalar magnetometers offer high sensitivity but have higher power requirements and therefore suffer a weight penalty relative to fluxgate types. Fluxgate magnetometers are vector sensing and their sensitivity is limited, mainly by thermally induced mechanical and electronic drift. This paper describes the development of a 1-m separation, vertical component, fluxgate magnetometer that alleviates these problems. Single and multiple array gradiometer configurations are presented, together with a description of data logging software developed to enhance survey efficiency. Survey data acquired during trials and testing are presented. The ergonomics of portable instrument surveying is also discussed. Copyright © 2003 John Wiley & Sons, Ltd.