Abstract
Geophysical surveying is widely used for the location of subsurface features. Current technology is limited in terms of its resolution (thus size of features it can detect) and penetration depth and a suitable technique is needed to bridge the gap between shallow near surface investigation using techniques such as EM conductivity mapping and GPR commonly used to map the upper 5m below ground surface, and large features at greater depths detectable using conventional microgravity (>~5m below ground surface). This will minimise the risks from unknown features buried in and conditions of the ground during civil engineering work. Quantum technology (QT) gravity sensors potentially offer a step-change in technology for locating features which lie outside of the currently detectable range in terms of size and depth, but that potential is currently unknown as field instruments have not been developed. To overcome this, a novel computer simulation was developed for a large range of different targets of interest. The simulation included realistic noise modelling of instrumental, environmental and location sources of noise which limit the accuracy of current microgravity measurements, in order to assess the potential capability of the new QT instruments in realistic situations and determine some of the likely limitations on their implementation.The results of the simulations for near surface features showed that the new technology is best employed in a gradiometer configuration as opposed to the traditional single sensor gravimeter used by current instruments due to the ability to suppress vibrational environmental noise effects due to common mode rejection between the sensors. A significant improvement in detection capability of 1.5–2 times was observed, putting targets such as mineshafts into the detectability zone which would be a major advantage for subsurface surveying. Thus this research, for the first time, has demonstrated clearly the benefits of QT gravity gradiometer sensors thereby increasing industry's confidence in this new technology.
Highlights
Geophysical surveying is widely used for the location of subsurface features and is of key importance for civil engineering (Metje et al, 2011), archaeology (Wynn, 1986), mineral exploration (Watson et al, 1998), environmental studies (Styles, 2012), in the petroleum and hydrocarbon industry (Berger and Anderson, 1981; Finch, 1985) and for unexploded ordinance management (Butler et al, 2002)
As the Quantum technology (QT) sensor measures an absolute value of gravity rather than a relative value and readings are theoretically comparable between different instruments, one solution on small scale sites may be to use two instruments; one static instrument to record ambient environmental noise and second rover to collect the points in a ‘variometer’ configuration similar to similar configurations used in magnetometry surveying (Becker, 2001; Vershovskii et al, 2006)
The results show that with careful corrections, the new sensors an improvement of detectability of a factor of 1.5 to 2.0 is achievable resulting in the ability to detect smaller buried features at depths beyond the limitations of existing geophysical sensors
Summary
Geophysical surveying is widely used for the location of subsurface features and is of key importance for civil engineering (Metje et al, 2011), archaeology (Wynn, 1986), mineral exploration (Watson et al, 1998), environmental studies (Styles, 2012), in the petroleum and hydrocarbon industry (Berger and Anderson, 1981; Finch, 1985) and for unexploded ordinance management (Butler et al, 2002). These anomalies are taken to have detectable material contrasts which would be typical for expected targets using each technique. The technology is developing rapidly, and instruments suitable for use in field surveys are likely to be available in the very near future
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