Real-time tracking magnetic gradiometer for underwater mine detection

Quantum Magnetics (QM), in collaboration with the Coastal Systems Station (CSS), Naval Surface Warfare Center, Florida, is developing a magnetic real-time tracking vector gradiometer (RTG) for incorporation into an unmanned underwater vessel (UUV) built by Bluefin Robotics as part of the United States Navy buried mine hunter program. The UUV-RTG would detect the presence of mines in conjunction with the buried object scanning sonar (BOSS) system being developed by Florida Atlantic University (FAU). Both the RTG and the BOSS systems would be placed in the same UUV; used together, they would improve mine detection and reduce hits on clutter. The RTG uses high-resolution fluxgate magnetometers. Based on the three-sensor gradiometer (TSG) concept invented by IBM, it comprises three primary three-axis sensors and one three-axis reference sensor. The configuration cancels the large ambient magnetic field at the primary sensors, thus mitigating dynamic range and linearity requirements. An earlier version of the RTG has been demonstrated on land and used for preliminary at-sea measurements. The new RTG is more compact and designed to fit inside a 12" diameter UUV. The RTG sensor unit is oil-filled and is sealed from the UUV, which is flooded with seawater. The RTG electronics resides in a sealed air-filled container. The RTG is placed in the nose section of the UUV in order to minimize electromagnetic interference from noise sources such as batteries, motors and actuators at the rear. To achieve further noise mitigation, magnetic field and electric current sensors placed at appropriate locations inside the UUV gather signals from noise sources for noise mitigation in post-processing.