NSWC Pt. Barrow Geomagnetic Observatory
DANIEL S. LENKO, JOHN F. SCARZELLO, AND DAVID TAYLOR
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. The three magnetometer
sensor suites were placed on Air Force Long Range Radar Site Pt. Barrow property
and cables connected the sensors to a PC in the CMDL Barrow Observatory building
that controls the array and stores the magnetic information onto transportable
media that is mailed to Maryland for analysis.
Configured to form two orthogonal gradiometer axes, magnetic N-S and E-W,
with a 150 m baseline, each of the three magnetic sensor sites consists of actually
two types of magnetometers. The first and most sensitive is the He-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. In terms of
sensitivity, the He-3 sensor can resolve submilligamma magnetic data when two
sensors are configured as a gradiometer; here, a second He-3 sensor is used
to cancel out earth's magnetic field. The dynamic range accommodates magnetic
fields over 100,000 gamma, but the He-3 sensor is gradient sensitive which can
shorten the measurement time between pumpings. 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 He-3 sample updates (2.34 times a second) and the
fluxgate sensor can resolve about 0.1 gamma.
The geomagnetic noise collected by the previously mentioned system has been
characterized and used to develop and test noise reduction algorithms in an
effort to enhance advanced detection methods. Specifically, Pt. Barrow ambient
magnetic data has been "played" into detection software as a training
data set. Also, on occasions, data from the observatory was used to correlate
magnetic noise events at other locations throughout the world. In terms of the
observatory hardware, the arctic environment is quite harsh and, therefore,
cabling and sensor maintenance is in order. Also, computer and/or storage media
upgrades will be performed as funds permit.
In order to complete the current sunspot cycle, NSWC plans to support the
Pt. Barrow Observatory through the end of the decade.