Offshore UXO Survey

During the construction wind farms, the laying of cables and dredging activities in the seabed there is always the risk of encountering unexploded ordnance (UXO) from the Second World War. In suspect areas it is therefore necessary to carry out an offshore UXO survey before starting the activities.  

Divers
To carry out offshore UXO surveys, T&A Survey has a team of specialized ex-marine UXO experts and certified divers. The UXO experts also take a leading role during the implementation of the project. If, for example, during dredging activities an object gets stuck in the suction nozzle, they can identify and secure the object on the spot. This way extra expenses due to stagnation of the activities can be significantly reduced.  

Data analysis
T&A’s UXO experts start with the data analysis on board of the ship. By combining all the measurement results, suspect objects can be located with great accuracy. Based on the outcome, the principal can make the decision, if necessary, to relocate the activities or have the objects identified and removed.


Multibeam echo sounder, Sidescan sonar and Multiprobe gradiometer
By being dragged along by a survey vessel, these geophysical measuring techniques make it possible to create detailed maps of the waterbottom.

  • The multibeam echo sounder maps the water depth; local deviations in detph may indicate the presence of a large object on the waterbottom,
  • The sidescan sonar is even more accurate in visualizing objects on the bottom of the sea in great detail.
  • The multiprobe gradiometer determines whether the objects detected by the multibeam echo sounder and sidescan sonar consist of ferrous material. It's magnetometers are also able to look several meters deep into the water bottom.

ROV and AUV
The offshore UXO survey is performed from a ship using an ROV (remotely operated underwater vehicle) and/or AUV (autonomous underwater vehicle) and several measuring techniques. The ROV for example is equipped with a rack of 8 to 12 gradiometer probes, a short-range sonar and a camera.