NSWC Point Barrow Geomagnetic Observatory
John F. Scarzello and Daniel S. Lenko
Naval Surface Warfare Center, Carderock Division, Electromagnetic Fields Branch,
West Bethesda, Maryland 20817-5700
The purpose of the observatory is to measure and characterize geomagnetic field variations using a sensitive magnetometer array for a period of at least one sunspot cycle.
The system was first installed in the spring of 1991 during Office of Naval Research (ONR Code 321SI) sponsored experiments. Three magnetometer sensor suites were placed on Air Force Long Range Radar Site Point Barrow property. The cables connected the sensors to a PC in the Climate Monitoring Diagnostics Laboratory (CMDL) Point Barrow building that controls the array and stores the magnetic information onto transportable media that is mailed to the Naval Surface Warfare Center (NSWC) for analysis.
Configured to form two orthogonal gradiometer axes, magnetic north-south and east-west, with a 152-m (500-ft.) baseline, each of the three magnetic sensor sites consists of two types of magnetometers. The first is the Helium-3 total field magnetometer which is an optically pumped, nuclear magnetic resonance sensing device. It provides a very accurate "absolute" measurement of the ambient magnetic field in the bandwidth from DC to about 0.1 Hz. The Helium-3 sensor can measure sub-milligamma (1 gamma = 1 nanotesla (nT) = 10-5 Oersted) magnetic fields when two sensors are configured as a gradiometer, to cancel out Earth's magnetic field. The dynamic range accommodates magnetic fields over 100,000 nT, but the Helium-3 sensor is gradient sensitive which can shorten the measurement time between optical pumping, leaving gaps in the otherwise continuous data. The second magnetic sensor included in each location is a triaxial fluxgate magnetometer. The three orthogonal axes measure magnetic fields in a bandwidth from DC to about 1 Hz. The digital data is appended to each of the Helium-3 sample updates (2.34 times a second) and the fluxgate sensor can resolve about 0.1 nT.
Some of the geomagnetic noise collected has been characterized and used to develop and test noise reduction algorithms in an effort to enhance detection methods. Also, on occasions, data from the observatory were used to correlate magnetic noise events at other locations throughout the world. Because the arctic environment is quite harsh, cabling and sensor maintenance are in order. Also computer and storage media upgrades will be performed as funds permit.
In order to complete the current sunspot cycle, NSWC plans to support the
Point Barrow observatory through at least the end of the decade.
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