Survey Blog from the R.V. Tom Crean
Hi, my name is Felix Butschek and I am PhD student based in University College Cork and undertaking part of my training on the Marine Institutes’ Cullen Scholarship programme. I have been lucky enough to join an INFOMAR survey, just the second conducted on the recently delivered R.V. Tom Crean, Irelands’ purpose-built 53 m national research vessel. The survey, led by the offshore mapping team based at the Marine Institute, was seafloor mapping in the western Celtic Sea for 10 days. During my time onboard I was able to learn from Fabio Sacchetti, Kevin Sheehan, Oisin McManus and Tommy Furey — some of the most experienced surveyors in Ireland, with over 50 years of combined offshore experience. I've been on a few surveys before and acquired multibeam data, but this operation is at a different scale.
INFOMAR aims to deliver a complete map of Ireland’s coastal and offshore waters by 2026. This is no small feat, given that Ireland's maritime area is among the largest in Europe. Over the past twenty years, 80% of it has been mapped at high resolution using an array of state of the art hydrographic sensors including Multibeam Echosounders (MBES). These incredibly nifty pieces of kit send a sound wave through the water column, forming a wide swath, effectively scanning for the seabed which will simultaneously reflect hundreds of acoustic beams. These return signals are picked up by transceivers. The time between transmission and reception is measured which allows the depth of the seabed to be accurately recorded.
The data generated through this effort are enormous. We process the raw data files as each survey line is completed while continuously progressing the survey. A dedicated, powerful desktop PC is used to identify and remove data outliers, check for shipwrecks and adjust for the effects of changes in seawater properties (that are measured periodically). The PC has enormous processing capacities, in sharp contrast to my own first computer from the late 1990s, which had an Intel Pentium II processor and about 128MB of RAM. However, even this powerful high-end computer struggles to quickly process all the hydrographic data we collect, simply because of its sheer volume, and process intensive operations. So much so, that it is hard to fathom how long processing such data would have taken thirty years ago. Perhaps this is why mapping the earth's seabed has been so long coming. We knew a lot more about the surface of the moon (and in fact many other planets) 20 years ago than our ocean's seabed but that is changing now as technology improves as do global seafloor mapping initiatives. The first moon landing was also allegedly completed on less processing power than is contained in your car keys. Let's take this as evidence that ocean science is more difficult! Speaking of the moon, we found a crater in about 190 m of water depth, measuring about 200 m in diameter and 5 m in vertical relief. It's almost perfectly circular — what could have caused it? Well without further information we can’t be sure but it could be the result of an ancient pocket of methane gas bubbling through the seafloor and leaving a crater-like scar in our geological past.
We also found several previously uncharted shipwrecks upon which we conducted a high-precision survey and reported these to the UK Hydrographic Office and the Underwater Archaeological Unit. While they are of no concern to navigation in water depths of 150-200 m, it is important to record the locations of these shipwrecks which form an important part of our marine heritage. INFOMAR maintains a database of over 400 wrecks, each with their own story and some of which are the final resting places of those that lost their lives at sea.
There are many more features of interest on the Irish seabed and which can be identified using our sonars; cold-water corals that formed mounds in the deep over millennia, icebergs that ploughed through the continental shelf during the last glaciation and gas seeps that created pockmarks and carbonate reefs. Irelands’ seafloor contains an incredible geo-diversity which in turn forms part of the basis for rich ecosystems. With the completion of Irelands’ seabed mapping programme in sight, this country is at the forefront of ocean science and is providing integrated mapping products which improve our understanding of key earth systems and contribute to the sustainable management of our shared marine resource.