Surveying the Black Sea to Uncover Ancient Secrets
Located between southeastern Europe and the far western edges of Asia, the Black Sea is an inland waterway that is approximately 168,500 square miles in size, with a maximum water depth of approximately 7,218 feet. Today and over many centuries, the Black Sea has been a critical commercial waterway that connects to the Mediterranean Sea.
Against this backdrop, an international team that includes the University of Southampton’s Centre for Maritime Archaeology and other research and academic institutions, is surveying the Bulgarian waters of the Black Sea, where thousands of years ago large areas of land were inundated as the water level rose following the last Ice Age. The project is referred to as Black Sea Maritime Archaeology Project (Black Sea MAP). The whole project is being coordinated by U.K.-based EEF Enterprises Limited (EEFE), a company established by the Expedition and Education Foundation.
MMT, a Sweden-based technology and services company for marine surveying, supplied the main vessel used by the Black Sea project in 2016. “Our owners have a long relation with the universities, supporting their research with survey resources,” says Joakim Holmlund, offshore manager at MMT. “The resources are far too expensive for universities to afford under normal circumstances. The Black Sea MAP project overall is being funded by the Expedition and Education Foundation over a period of three years; in 2016, MMT contributed the survey/ROV vessel Stril Explorer.
Mapping Underwater Landscapes, Finding Shipwrecks
Holmlund says the main purpose of the Black Sea mapping project is to map underwater landscapes.
Through surveys of the Bulgarian waters, the Black Sea MAP is investigating what happened when large areas of land were inundated post Ice Age, how rapidly and what effects it had on human populations living in the region, questions that are still hotly debated. To do so, they are carrying out geophysical surveys to detect former land surfaces buried below the current sea bed and taking core samples to characterize and date them.
It was the discovery of more than 40 ancient shipwrecks during the expedition that first attracted media attention. “Using the latest 3D recording techniques for underwater structures, we’ve been able to capture some astonishing images without disturbing the sea bed,” says Jon Adams, founding director of the University of Southampton’s Centre for Maritime Archaeology and principal investigator on the Black Sea MAP.
“We are now among the very best exponents of this practice methodology and certainly no one has achieved models of this completeness on shipwrecks at these depths.”
Underwater Technologies that Facilitate Mapping
Like Adams, MMT’s Holmlund sees advances in remotely-operated vehicles (ROV) and in photogrammetric and visual imagery techniques as enablers of these underwater discoveries — as well as of the mapping of the Black Sea floor.
The team’s research ship for 2016 was the Stril Explorer, a state-of-the art offshore survey vessel equipped with the most advanced underwater survey systems in use anywhere in the world. They are carried on two ROVs. The Supporter ROV is optimized for high-resolution 3D photogrammetry and video. The SROV Surveyor Interceptor is a revolutionary vehicle developed by the Norwegian ROV manufacturer Kystdesign, together with the survey companies MMT and Reach Subsea. It flies at three times the speed of conventional ROVs and carries an entire suite of geophysical instrumentation, as well as lights, high-definition cameras and a laser scanner. In the course of the project it has set new records for both depth (1,800 meters), sustained speed (over 6 knots), and has covered a distance of 1,000 kilometers.
Hydrography, which measures and describes the physical features of oceans, seas, lakes and rivers, and the connecting coastal areas, primarily by surveying with multi-beam echo sounders, was also an important technology used in the Black Sea project.
“You measure spread of several hundred well-defined sonar pulses simultaneously. The reflection of the sound pulses builds up a three-dimensional image of the seafloor, revealing any man-made objects that once ended up resting on top of the seafloor,” Holmlund says.
Doing seabed mapping in the Black Sea produces a great challenge; the Black Sea basin is deep and often has bad visibility. Coming down to 1,800 meters the visibility is sometimes obscured by the so-called “marine snow” biological material that slowly falls through the water from surface down to the deeper water. In addition, the water is very aggressive to the equipment due to the high content of hydrogen sulfur in the deeper anoxic waters.
The task to map large areas of seabed and then go in to detailed investigation of the findings requires a large and technically complicated toolbox. In the Black Sea project, the ship’s hull mounted sonar system was combined with two ROVs equipped with geophysical instrumentation and camera systems. The largescale investigation of the seafloor was followed up by detailed investigation of selected targets using both ROVs. The ROVs have “unlimited” time on the seafloor, can go down to several thousand meters water depth and carry loads of equipment, replacing divers or submarines, hence minimizing the risk with accidents involved in complicated diving.
In all, the Black Sea project has been a great success so far. The new technique carried by MMT’s ROVs made it possible to map an enormous area and each site visited was mapped in detail with several thousand images, building detailed 3D models including textures. The technique used in the Black Sea for the archaeological expedition is also used by MMT in other commercial/infrastructure projects, working in renewable wind power industry or offshore oil and gas market where the demands for higher resolution and quality data steadily increase.