The Mag648S from Bartington Instruments Ltd., Oxford, U.K., is a submersible, low-power, triaxial magnetometer designed primarily for use in surveillance systems, including harbor and coastal applications. The sensor uses fluxgate technology to provide low-noise operation; standard noise is 11–20 pTrms/√Hz at 1 Hz while low noise is ≤10 pTrms/√Hz at 1 Hz. The 92.5 mm by 45 mm dia. device is submersible to 2000 m, has a 12 yr. MTBF, and operates from a 4 V power supply.