Wednesday, March 30, 2016

How Satellites Find Shipwrecks From Space

This is actually a small start on the bigger problem of discovering all possible anomalies for archaeology.  Most of those ships were wood but left disturbances and sunken ballast as least.  That sunken ballast will locate almost any wooden ship.  Then if we are lucky clay products will have survived at least.

As we have posted, the Bronze Age saw commercial shipping operate on a number of clear routes on a seasonal basis.  We have the obvious Gibraltar to the eastern Mediterranean route to work and that continued all through history depending on a number of port cities around the littoral of this sea.

We then have the westerly Seville to Cuba route that was used after contact and also through the Bronze Age itself.  The return trip however used the gulf stream to the isle of Lewis or its latitude at least.  I Lyonese still existed then it is the more likely first destination while Lewis acted as a pivot point for entering the Irish Sea.

Then we have Bronze Age travel through Suez  to India as well and additional routes to south africa and ultimately through to China.  All have predictable areas of interest in which ships foundered without been ground up on some beach or reef.

In the event, mud and sand provides a homogeneous return signal and penetration will disclose a foreign rock reef formed by a ballast. That will be worthwhile..
How Satellites Find Shipwrecks From Space

By Rossella Lorenzi, Discovery News | March 14, 2016 01:13pm ET

Long sediment plumes extend from the wreck sites of the SS Sansip and SS Samvurn i this image from the NASA/USGS Landsat satellite.Credit: NASA/USGS Landsat/Jesse Allen/NASA Earth Observatory/Matthias Baeye et. al.

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.

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