The uncontrolled detonation of unexploded ordnance (UXO) is still a present-day risk in coastal and offshore marine environments. As part of UXO risk management, an appropriate geophysical survey is required to assess and mitigate risks. The Fugro Geowing has been designed to collect high resolution magnetic data for UXO surveys.

The 5 m wide Geowing frame comprises five caesium vapour magnetometers in a two row configuration. These are mounted behind a remotely operated towed vehicle (ROTV). The ROTV has the ability to accurately track the seabed at a set altitude, helping to reduce the number of vertical infill lines to a minimum.

The Geowing’s ability to track the seabed at a set altitude also allows for a smaller distance between the sensors and an object, allowing a greater magnetic signature to be received from ferrous objects. Greater vertical control allows for more consistent gridded and modelled results. This is aided by the number of magnetometers and their arrangement within the 5 m wing, providing increased resolution.

We have developed advanced processing techniques for use with the Geowing gradiometer set-up. It differs from a conventional magnetometer configuration in that it allows the geophysicist to manually calculate the X, Y and Z gradients. The analytical signal is then derived from the three gradients. This approach minimises background noise and false positives, ultimately reducing the number of potential UXO targets that require further investigation.

The Geowing can detect buried ferrous objects at a variety of depths. The detectability of an object depends on the type, shape, size, orientation and ferrous mass of the object. In principal, anything with ferrous content can be detected provided the line spacing and altitude above the object are small enough to ensure that detected anomaly size exceeds the background level. We work closely with UXO consultants that conduct desktop studies to determine UXO risk, type and ferrous weight. Once this is known, the survey parameters can be set.

  • Seabed tracking accurate to 0.2 m
  • Reduces the requirement for infill (and operational time)
  • Real-time measurement of the vertical and transverse gradient
  • Minimises the effect of underlying geology and background noise
  • Reduces false positives and the requirement for further investigation

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