According to UNESCO estimates, there
are as many as 3 million shipwrecks spread across the ocean floors, and a
great many of those reside in coastal regions, where they pose
significant danger to passing ships. New research has found that it
might be possible to spot coastal shipwrecks by searching for plumes
of sediment in imagery collected by NASA's Landsat 8 satellite.
The risk posed by shipwrecks to passing vessels is significant, so much so that in 2012, the Council of Europe's Parliamentary Assembly recommended that North Atlantic waters be mapped and monitored. The problem is, that while knowing exactly where each and every sunken ship resides would certainly be advantageous, the actual process of mapping them out isn't all that easy.
In the past, researchers have used lidar (which uses pulses of light to measure distance) to map coastal regions, and sound-based methods such as echosounders can be used in deep water. But the cost involved in blanket-mapping regions using such methods is too high to make them practical options.
Now, a team of researchers from the Royal Belgian Institute of Natural Sciences, Ulster University in Northern Ireland and the Flemish Agency for Maritime and Coastal Services, has turned to freely available Landsat data to help provide a cost-effective widespread solution.
The research focused on a coastal area near the Belgium port of Zeebrugge, making use of data from a previously conducted echosounder survey of the region to pinpoint four fully submerged shipwrecks. They then used 21 Landsat 8 images, combined with tidal models, to map the sediment plumes that extend from the wrecks.
Of the four wrecks, the two that had significant portions of their structure unburied were found to create easily trackeable sediment plumes. Studying the data, the researchers concluded that pits in the structures fill with sediment during calm periods, with that sediment then surfacing and forming detectable plumes during flood and ebb tides.
While the researchers were looking at known shipwrecks during the study, they believe that their methodology could be used in reverse to identify uncharted wrecks, by picking out sediment plumes and tracing them back to their source. In the long run, it could provide an effective means of mapping coastal regions, without the need to conduct expensive surveys.
The findings of the work are published online in the Journal of Archaeological Science.