ADUS DeepOcean has been at the forefront of research into maximising the potential of multibeam sonar for the investigation of shipwreck sites. This includes developing survey methodologies to improve the quality of the survey data together with software to produce enhanced visualisations of wrecks and other submerged man-made structures.
ADUS DeepOcean has experience of a wide variety of equipment involved in high-resolution multibeam surveying and has learnt that the best equipment helps to provide the best results. Typically we would use a Reson SeaBat 7125 SV2 coupled to an Applanix POS MV 320 Inertial Navigation System (INS) in a waterproof housing for shallow water surveys and a Reson SeaBat 7125 ROV2 coupled to an IxBlue PHINS 6000 INS when using a Remotely Operated Vehicle (ROV) when surveying in deeper water. We continually monitor the specification of new products, as they become available and field test whenever they are made accessible to us.
The ADUS team recognised many years ago that to collect the highest quality data there were numerous factors (74 identified so far) that needed to be addressed. One of the key considerations was the difficulty of accurately measuring lever arm offsets between the reference points of the sonar head, the motion reference unit and the GPS antennas on vessels of opportunity. As many of our surveys utilise vessels of opportunity we have developed a deployment system that can be quickly set up on vessels ranging in size from small inflatables to large research ships. This ISHAPS (Independent Sonar Heading, Attitude and Positioning System) is modular so that it can be lengthened or shortened to suit the size of the survey vessel and also to optimise the range. The only variable is the Z coordinate value, which changes with the length of the ISHAPS. Example of ISHAPS deployment can be seen in the gallery below.
Since the introduction of mobile laser scanning to ADUS DeepOcean’s armoury, we can now incorporate both underwater and surface laser equipment onto the same ISHAPS structure as the multibeam. Below is a link to a drawing of the set up for one phase of our Costa Concordia survey with equipment angled partially or totally to one side to improve the recording of the vertical faces of the wreck.
ADUS DeepOcean have used a wide range of ROVs as a survey platform, the smallest being a Saab SeaEye Falcon, with additional buoyancy, which was used for a trial multibeam survey on a wreck in 30m of water. Data was collected but the vehicle was difficult to control and the experiment will not be repeated!
All of our other ROV-based surveys have used conventional work class vehicles similar to the NATO submarine Rescue ROV, below, which was used for our survey of the Russian nuclear submarine B-159 in 250m of water in the Barents Sea.
Surveys involving a full work-class ROV spread require a dedicated support vessel, which makes them relatively expensive to deploy, but it is an effective way of getting high-resolution multibeam data at depth. The deepest multibeam survey ADUS DeepOcean has undertaken so far was in 1500m of water on the Deepwater Horizon, the semi-submersible oilrig that sank in the Gulf of Mexico.
Very deep water operations are always likely to require large, powerful ROVs but, to reduce the cost of multibeam surveys in water depths beyond the range of surface-mounted systems down to 500-600m, ADUS DeepOcean is currently developing a range of simpler Remotely Operated Towed Platforms (ROTPs) that have the payload of the largest conventional ROV but can be operated off a smaller, cheaper vessel. Our 0-200m range ROTP can be deployed from almost any boat with an A-Frame, even as small as something like a 12m catamaran.
Understanding what influences the quality of multibeam survey data has been a continued priority of ADUS DeepOcean since recognising that a number of marginal gains, each almost insignificant in itself, can provide a step change in overall data quality and, so far, we have identified 74 individual factors that have an impact on the end results. This attention to detail is one of the reasons why ADUS DeepOcean produces the best wreck visualisations – the evidence can be found by searching search Google Images for multibeam sonar wreck images. There will be some images from other survey teams that superficially look good as thumbnails but if you enlarge most of these their poorer quality and lower data density soon becomes apparent.
For a high level of detail in subsea surveys the density of the surveyed points needs to be considerably higher than required for the highest standard of seabed surveys as identified by the International Hydrographic Organisation. The IHO special Order survey requires more than nine hits on a 1m cube whereas ADUS DeepOcean multibeam structural surveys normally collect between 250 – 2000 points in a 1m square at a range of 10m with just one pass. Most survey teams sometimes achieve something close to this level of density by combining data from multiple passes. Unfortunately this technique results in fuzziness when surveying complex structures because the motion reference and positioning technology currently available for multibeam surveying is just not sufficiently precise to give millimetre-perfect alignment between different passes.
The density provided by underwater laser can be even higher than that from multibeam sonar and the resulting metrical data provides visual imagery with a high level of detail.
Below is a detail from a shipwreck showing rope ladders and other debris, including a life raft in its container.
The academic background of the founders of the company ensures that every survey project is also used as a platform for research into improving end results, efficiency and cost effectiveness. Enthusiasm for progressive improvements in the quality of survey data collected at sea is matched by the enthusiasm of the team involved in visualisation research funded by ADUS DeepOcean, based in the University of Dundee under the direction of Professor Chris Rowland, one of the founders of the company.
I have, and remain, a keen supporter of ADUS and the high resolution surveys that you have performed.
ADUS has brought something novel to the industry and wherever it is exhibited, it has drawn interest as I am sure you know.David Pockett - Marine Consultant LOC Marine & Engineering Constultants