Searching for seafloor ordnance by sending out a vessel with divers and equipment is very expensive, so companies are trying as much as possible to employ geophysics to provide a solution and lessen human involvement. Typically they’ll use Seequent’s Oasis montaj with the UXO Marine extension to pull together the vast amount of data gathered by the surveys.
Not only can this software configuration do all the processing, visualisation and target generation, but it can also bring in all the other data sets that might be available – sidescan, profiler, multibeam and so on.
You can start to layer up an interpretation of what your survey area is looking like, then bring in your bathymetry and all your other geophysics methods underneath, to get a better understanding of what that anomaly is down on the seabed. Is it an anchor, a spooled-up chain, some debris a fisherman has thrown over the side, or might it potentially be a UXO? All of that will be displayed on a colourful map with nice clear blobs for where the anomalies are.
Making sense of the iron harvest
Magnetics, as a science, will help you detect anything with a ferrous content, and because of the ages of these munitions, most will have been cast from iron. The big challenge is trying to decipher between each of these ferrous items and make sure the client can focus on the real risks rather than having to check every single piece of scrap on the seabed.
Once you know how deep the object is buried, its size and its orientation within the seabed, analysis of that data can sift out the anomalies most likely to be worth studying more closely. You can give the client a GPS location, then they can investigate further with an underwater ROV (Remotely Operated Vehicle) directed by a pilot on a nearby vessel, or even back on land. That ROV will have a geophysics instrument on the front, or a sub-bottom imager, and will gain a deeper understanding of what that anomaly is. And if it is a bomb? In fact it rarely makes sense to remove what’s found, or blow everything up on site. It’s easier to leave it where it sits and put your windfarm somewhere else. Ultimately that means the windfarm can be redesigned slightly to avoid the problem, or maybe moved altogether if there’s a dump or a huge munition in the area. The risk is reduced, and the project can move ahead.
The next step for seafloor surveying
We’ve learned there is plenty of UXO on the seafloor – really, a lot – and in the future there will be an increasing requirement from contractors in this sector to narrow down the target list to the anomalies that are genuinely important.
Because of the way contracts are drafted, there has been a tendency for contractors to err on the side of safety and present a target list that could run into the thousands for further investigation. For example, there are certain parts of the North Sea that have boulder fields with a slight magnetic signature, and some companies will recommend checking every single boulder. Thousands and thousands of them… But that’s becoming unacceptable. The pressure is on to bring those numbers down.
There are a couple of interesting directions the technology could go in to address that. You could introduce electromagnetics. It’s rare in the industry at present, but has the capability to classify the munition more accurately.
Then I think there are possibilities for machine learning, using AI to rattle through the data and identify signatures for you.
There are multiple ways this could go, and better classification is definitely something the industry would welcome. If it helps make the creation of clean energy easier, more cost efficient, and with less risk, that will be an important and valuable contribution.