Dredging seen from outer space

Together with Belgian consultancy firm IMDC, VITO created a software package that allows dredging companies to closely monitor the sediment levels before, during and after dredging works by using satellite images.

During the dredging process, a lot of sediment is churned up from the seabed through digging or suction. Dredging firms invest in specific machines or techniques to limit the spread of sediment. This helps them prevent or limit the impact on fauna and flora in the water and on the nearby land. “A sediment plume can drift over to an ecologically valuable coral reef or mangrove area. To protect vulnerable ecosystems, most countries have standards to limit sediment concentrations on such sites,” project leader Els Knaeps of VITO says. “If those limits are exceeded, the dredging firm has to intervene or, in the worst-case scenario, halt the dredging works to avoid fines. Excessive sediment concentrations can also be caused by natural phenomena such as storms or intensive rainfall. Satellite images help dredging firms to analyse the exact cause of such excesses.”

Satellite data

The software created by VITO and IMDC (International Marine Dredging Consultants) uses NASA (National Aeronautics and Space Association) and ESA (European Space Agency) satellite data. “Dredging firms use boats or buoys that test the sediment levels in specific places and make predictions using models. Those methods are still important, but they only offer a limited view of the sediment levels in the entire dredging area, both temporally and spatially,” Knaeps explains. Satellite images are a useful addition. “Dredging companies can deduce the natural background levels from earlier satellite images and use them as a reference point. During the dredging works, the sediments in the entire area can be monitored with current, multi-spectral satellite images.”

Through the clouds

VITO is responsible for validating and calibrating the remote sensing models. In the next years, VITO wants to add new satellites. Els Knaeps: “In January 2016, the European Sentinel 2 satellite will be added to the network. Sentinel 3 is next, sometime in 2016. In December 2015, a feasibility study was launched with the support of BELSPO (BELgian Science POlicy) and ESA to integrate the Belgian PROBA-V-satellite into this form of remote sensing. As such, the existing products can be offered more frequently and with more spatial detail. Drones also play a role. On cloudy days, they can still take useful pictures. We already experimented in the ports of Zeebrugge and Antwerp. The drones can take off from the dredging ship and take digital camera pictures. Using that material, we can create a detailed sediment chart.” Mark Bollen, project engineer at IMDC: “We offer dredging firms and energy concerns an online web service called ‘MAST’ (MArine Supervision Tool). This service allows them to use the information stream to make decisions onsite and manage the works in an environmentally friendly manner. The bundle contains weather forecasts, shipping data and, thanks to VITO, also information we have gathered through remote sensing. At IMDC, we have been working with VITO for 10 years, and we are very proud to be able to offer this product together.”

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