Polatomic (funded under a Small Business Innovation Research Project) has produced a conceptual plan and design for a novel and advanced laser scalar gradiometer (LSG) for use in detecting, classifying, locating and monitoring various military targets of interest. These targets include submarines, mines, underground facilities, buried missiles, or tanks obscured by trees of buildings. The LSG sensor can detect through the land or sea barriers since magnetic fields are not distorted or attenuated by the air to land or sea boundaries. A noise level of 0.3 pT√Hz has been demonstrated based upon field and airborne measurements of the Polatomic 2000. This is a 10× improvement in noise level in comparison to any airborne magnetometer in use today. If this noise level is fully utilized it can accomplish submarine detection ranges that are three times greater than those accomplished in the fleet today. A gradiometer with 0.3 pT/√Hz-metre sensitivity (1 metre sensor separation) in the 0.03-1 Hz frequency band is also possible. This LSG gradiometer would have a sensitivity that is a factor of 10× more sensitive than the most sensitive vector gradiometers built today. When the LSG noise levels are achieved in the mine counter measure (MCM) target environment, a 1.7× range improvement over the best vector gradiometer ranges could be achieved. The 0.3 pT/√Hz-m noise level will be accomplished by placing two Polatomic 2000 laser-pumped electron spin total field helium4 cells one metre apart. Tests at the Polatomic magnetic facility have demonstrated the unit cell noise level of 0.2 pT√Hz is not affected by separations up to and exceeding three feet. Polatomic 2000 airborne and magnetic test facility data have both demonstrated gradient noise levels less than 0.3 pT/√Hz with spacing of one foot in the 0.03 Hz-50 Hz bandwidth. It is expected that ancillary sensors to detect motion will be required to achieve a sensor noise level of 0.3 pT√Hz-metre in the MCM or anti-submarine warfare environments. The self-motion noise from the sensor is expected to be very low, but magnetic contamination from the sensor electronics and supporting tow or unattended airborne or underwater vehicles - will require ancillary sensors for magnetic motion compensation. Other environmental effects such as magnetic wave noise, magnetic water flow noise, dissimilar metal noise from nearby sources and the Earth's geologic magnetic field may be coherently reduced by ancillary sensors or may limit the operational detection range.
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