Abstract
Abstract. Efficient and accurate acquisition of magnetic field and gradient data have applications over a large range of environmental, archaeological, engineering, and geologic investigations. Developments in new systems and improvements in existing platforms have progressed to the point where magnetic surveying is a heavily used and trusted technique. However, there is still ample room to improve accuracy and coverage efficiency and to include reliable vector information. We have developed a vector magnetic gradiometer array capable of recording high-resolution field and gradient data over tens of hectares per day at 50 cm sensor spacing. Towed by an all-terrain vehicle, the system consists of eight vertical gradiometer sensor packages and incorporates differential GPS and an inertial measurement system. With a noise floor of around 6 nT at 15 km/h towing speed and 230 Hz sample rates, large areas can be mapped efficiently and precisely. Data are processed using a straightforward workflow, using both standard and newly developed methodologies. The system described here has been used successfully in Denmark to efficiently map buried structures and objects. We give two examples from such applications highlighting the system's capabilities in archaeological and geological applications.
Highlights
Ground-based magnetometry has been a staple for environmental geophysics for decades
Most systems (e.g. Geometrics 858, Sensys MXPDA, or Gem Systems GSM-19) utilize Overhauser (Hrvoic, 1989) or alkali vapour (Hardwick, 1984) total-field sensors; i.e. the sensors measure the scalar magnitude of the magnetic field
This has the benefits of providing stable, absolute measurements insensitive to sensor orientation when measuring the magnetic field and minimally sensitive when measuring the total vertical gradient, i.e. the vertical gradient of the total field, or TVG
Summary
Ground-based magnetometry has been a staple for environmental geophysics for decades. Simple but accurate detection of a large anomaly is sufficient, for example finding capped, abandoned wells (Kaminski et al, 2018). Other applications, such as in multipole expansion in UXO discrimination (Sanchez et al, 2008) or detailed archaeological investigations, require densely sampled data of high quality. Most systems (e.g. Geometrics 858, Sensys MXPDA, or Gem Systems GSM-19) utilize Overhauser (Hrvoic, 1989) or alkali (often caesium) vapour (Hardwick, 1984) total-field sensors; i.e. the sensors measure the scalar magnitude of the magnetic field. Like the US Geological Survey TMGS system (Bracken and Brown, 2005) or the Foerster Ferex (https://www.foerstergroup.com, last access: 26 November 2021), use fluxgate sensors (Gavazzi et al, 2016), which are inherently vector sensors and have a lower power consumption relative to traditional alkali vapour systems
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