This has been a particular area of interest over recent years, particularly in the field of non-ferrous UXO detection and improving efficiency in detection and identification over large areas. Bibby HydroMap have invested significantly in developing efficient magnetometer towing configurations over large areas, which have involved multiple EIVA ScanFish Katria wings capable of accommodating up to four magnetometers on each system. Using hydraulic enabled boom arms, we are able to tow up to three systems simultaneously, providing a wide coverage without compromising density. Depending on the site and project requirements, this configuration can be altered to reduce the number of magnetometers, increase the spacing between Scanfish and extend or reduce the boom arm length, providing versatility.
Bibby HydroMap Operations Manager Tom Davenport comments:
"This has been a real area of focus, and we are confident we have a system that can react to individual requirements, without compromising other datasets. We have been providing UXO surveys for many years, on a range of sites, and this represents a significant breakthrough"
The EIVA ScanFish is a semi-automated ROTV system, which responds to the marine environment to ensure the sensors remain stable, close to the seabed. With the horizontal control upgrade, infill is minimised as the units can be steered independently to allow for superior line keeping.
“Cost-effectiveness and the possibility of customisation constitute a key focus for all product development activities in EIVA, as we aim to further improve the competitiveness of our customers. We are therefore happy to see how the flexible Bibby HydroMap ScanFish configuration has succeeded in these areas through the close collaboration between EIVA and Bibby HydroMap in creating this unique multiple ROTV setup,”
said EIVA CEO Jeppe Nielsen.
Following acquisition, the data is processed and interpreted using Oasis Montaj UX Detect, a system that Bibby HydroMap are very familiar with having worked closely with Oasis to develop specific algorithms and identification processes. Rather than moving whole heartedly towards automated target picking, we are certain that our manual technique using highly trained processing geophysicists has reduced the number of false positives, reducing valuable inspection time and offering a high success rate of detection.
Moving away from traditional, ferrous UXO identification using magnetometers to non-ferrous UXO detection, this has proven to be more of a challenge. Whilst there are numerous technologies that claim to solve the issue, there is not one that can be selected, certainly not to the same degree of acceptance as with the market-leading magnetometers.
Each has their own strengths, nuances, and capabilities, using a myriad of base technologies. Some are EM, a few parametric and non are truly ground-breaking, although when considering the objects that are being searched for it is no wonder. With minimal magnetic signal that depreciates rapidly with burial depth, non-ferrous UXO targets are often no more than a man-made shape, existing within a pre-identified target zone, with a suspected depth of burial based on age and site conditions. Luckily, or unluckily, depending on the viewpoint, these targets are likely to be of considerable size, and with an easy identifiable shape by a trained expert.
Focusing on the shape and size of the target, rather than relying on any magnetic signal, points towards acoustic data acquisition. With EM systems restricted to ROVs flying close to or being pulled along the seabed at slow speed, this seems like a clear benefit. The short range (>2m) of EM systems also discounts targets covered by sandwaves or lying in the wrong position. Considering acoustic options, there are a few, both ROV mounted and towed from the vessel. Towed systems are clearly heavily reliant on favourable weather, and restricted to shallow water, although can operate at a faster speed than ROV based systems.
Moving on to ROV mounted sensors, there is a clear benefit in that they are perhaps capable of intervention activity alongside survey, providing a visual on the target and the option for disposal. One ROV mounted acoustic system that we have had experience in the cable depth of burial survey sector is PanGeo's Sub Bottom Imager. This is a 3D parametric system that is capable of a maximum penetration of 8m, depending on seabed conditions, and provides excellent positional accuracy. The SBI is gaining traction in the non-ferrous market, and has been used on a number of UK wind farms ahead of full visual inspection and removal to identify targets for further investigation.
One of our Senior Geophysicists Theo Gaussen was on board for the project:
“In areas where there are is a high density of magnetic targets or a potential for non-ferrous UXO the Pangeo SBI has been used successfully. The system allows the geophysicist to determine the dimensions and depth below seabed of buried objects, if a magnetometer survey has been conducted the two datasets can be cross correlated. Once a target has been identified and if it is the correct shape to be of risk, further ROV dredging, visual inspection and removal/detonation can occur. When comparing the SBI interpreted size and depth of the object, this been found to be within +/- 0.2m of the removed object. The Pangeo SBI can provide accurate results, reducing the number of targets requiring visual inspection and ultimately saving in both time and cost to a project.”
The SBI has been successfully mounted onto d'ROP for a non-ferrous survey trial in 2015 on an east coast wind farm, in addition to a number of cable and pipeline depth of burial campaigns. d'ROP is our custom survey ROV which is deployed through the moonpool of our DP1 vessel Bibby Athena. The system gains base horizontal positioning from the vessel's DP, vertical position by the heave compensated umbilical winch and combined LARS, and it makes fine adjustments to its own position using the four onboard thrusters. Whilst the deployment method (underneath the vessel) deems visual UXO investigation too risky, surveying the target acoustically is both efficient and effective, working at a speed of 2 knots in up to 3.5 knots of cross-current. This far exceeds traditional ROVs, especially those of comparable size, as the d'ROP measures just 2m x 2m x 2m.
There are still improvements to be made within the industry in improving both acquisition efficiency and data quality, although there are strides being made to drive this process through on the Round 3 and European sites in development.