How Satellites Find Shipwrecks From Space
Distinctive linear plumes of these particles extend as far as 2.5 miles downstream from shallow shipwreck sites.
It's estimated that some three million shipwrecks are scattered across the oceans, with a quarter possibly resting in the North Atlantic. Now satellites can be used to help locate these lost ships, according to new research.
In a study published in the Journal of Archaeological Science, marine geologist Matthias Baeye at the Royal Belgian Institute of Natural Sciences and colleagues explain that wrecks produce Suspended Particulate Matter (SPM) concentration signals which can be detected by high-resolution ocean color satellite data such as NASA's Landsat-8.
Distinctive linear plumes of these particles extend as far as 2.5 miles downstream from shallow shipwreck sites and are therefore easily detectable from space.
"Landsat-8 data is free and therefore the method presented in the study is an inexpensive alternative to acoustic and laser survey techniques," Baeye and colleagues wrote.
The researchers began their study by analyzing four known wreck sites near the Port of Zeebrugge on the Belgian coast.
Located within 3 miles of each other on a sandy sea floor in less than 49 feet of water, the wrecks were all civilian vessels.
Two ships, the SS Sansip and the SS Samvurn sank after being mined during World War II. The Swedish steamship Nippon collided with another vessel in 1938, while the SS Neutron, a Dutch steel cargo vessel, went down in 1965 after hitting a wreck, presumed to be the SS Sansip.
Using tidal models and a set of 21 cloud-free Landsat-8 images, the researchers mapped sediment plumes extending from the wreck locations.
They found that SPM plumes originating from the sites of the SS Sansip and the SS Samvurn, which had substantial portions of their structure unburied, could be traced downstream during ebb and flood tides.
No SPM plumes were recorded in association with the SS Neutron and the SS Nippon, which are buried deeper in the seabed.
"SPM plumes are indicators that a shipwreck is exposed at the seabed and certainly not buried," Baeye and colleagues wrote.
According to the researchers, it's the exposed structure of the ships that creates scour pits around the wrecks. These act as sinks where fine-grained suspended material is deposited during slacks (the period of relatively still currents between ebb and flood tides).
The scour pits then act as sources for suspended material when the bottom current increases again. When the sediments reach the surface, they create the linear plumes.
It is not certain whether depth is a limit to the new wreck-detecting methodology since the four wrecks in the study all rest in relatively shallow waters. Satellites may not image plumes from deep sea wrecks.
Still, given the millions of shipwrecks scattered throughout the oceans, having one more tool to find them is significant.
"The ability to detect the presence of submerged shipwrecks from space is of benefit to archaeological scientists and resource managers interested in locating wrecks," the researchers concluded.
Image: Long sediment plumes extend from the wreck sites of the SS Sansip and SS Samvurn. Credits: NASA/USGS Landsat image/Jesse Allen, NASA Earth Observatory
Long sediment plumes extend from the wreck sites of the SS Sansip and SS Samvurn in this image from the NASA/USGS Landsat satellite.
A joint Greek-American archaeological expedition has discovered 22 shipwrecks around the small Greek archipelago of Fourni, revealing what may be the ancient shipwreck capital of the world.
Hailed as one of the top archaeological finds of 2015, the discovery added 12 percent to the total of known ancient shipwrecks in Greek territorial waters in just 10 diving days.
Shipwrecks were found literally everywhere. Over half of the wrecks date to the Late Roman Period (circa 300-600 A.D.). Overall, the shipwrecks span from the Archaic Period (700-480 B.C.) to the Classical (480-323 B.C.) and Hellenistic (323-31 B.C.) through the Late Medieval Period (16th century).
The cargoes revealed long distance trades between the Black Sea, Aegean Sea, Cyprus, the Levant, and Egypt in all those periods. At least three ships carried amphoras, or jars, that have not been found previously on shipwrecks.
The archaeologists mapped each shipwreck using photogrammetry to create 3D site plans. Representative artifacts were raised from each wreck site for scientific analysis.
Amphoras may go on displays in museums once conservation work is over.
The archaeologists have only examined about 5 percent of the archipelago's coastline, and are confident that many more wrecks will be discovered as they return to the islands next year.