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The objective of this demonstration was to address the lack of effective and proven approaches for conducting wide area assessment (WAA) of sites potentially containing underwater MEC. The WAA demonstration was performed at the South Beach Site off the south coast of Martha's Vineyard, MA. Tetra Tech developed and implemented an approach that utilizes multiple customized geophysical detection and mapping technologies and processing methods. These systems and methods include the use of multibeam, sidescan, and subbottom profiling sonars and a gradiometer array. The towfish platform used for collection of magnetometer data was the Marine Gradiometer Array (MGA), a custom designed seven sensor 4m wide true 3-D gradiometer, utilizing Overhauser magnetometers. The Overhauser sensor has been demonstrated to be effective for the location of MEC in marine and freshwater environments. The MGA, depth rated to 300m, successfully operated in 1-35m water depth while exceeding survey production rate estimates. Field survey costs were demonstrated to be as low as $2450 per hectare inclusive of all four geophysical data sets. |
