There may be as many as one million acres of the marine environment that are potentially contaminated by unexploded ordnance (UXO). These environments vary significantly with respect to water depth, sea floor morphology, and geologic regimes. Current deployment modes place sensors 1 to 2 m above the sea floor, restricting detection capabilities, equivalent to that of airborne platforms in terrestrial applications.
The objective of this project was to develop a High Temperature Superconducting Tensor Gradiometer (HTSTG) for detection and discrimination of UXO in the marine environment (in water depths up to 20 m).
The first milestone of this project was to demonstrate a sensitivity of 2 pT /m /√Hz at 10 Hz in laboratory conditions when measured in a mu-metal shielding enclosure. The second milestone was to demonstrate full tensor measurements while the system was both stationary and in motion under laboratory conditions.
For the first milestone, measured sensitivities of six gradiometers ranged from 1.25 pT rms/ m / √Hz to 2.28 pT rms/ m / √Hz at 10 Hz with four of the six achieving sensitivities of < 2 pT /m /√Hz at 10 Hz.
The second milestone proved more difficult to demonstrate:
The project team recommends further research to determine the compensation coefficients and to examine the benefits of operating a global feedback scheme using feedback coils with open coil structure. These developments could support an underwater demonstration of the extended detection range and characterization capabilities of the HTSTG system.
The system has inherently higher sensitivity and immunity to external noise than conventional magnetic sensor systems, thus improving detection performance in the difficult marine environment. The system also has enhanced characterization abilities as the location and magnetic moment of a target can be determined definitively by gradient tensor measurements at a few locations along a profile. This characteristic provides an advantage in the marine environment, which is difficult to regularly sample due to the effects of wind, waves and currents on the tow-vessel or deployment platform.