Geomagnetometer

Geomagnetometer

The PARI geomagnetometer is located at:

Longitude = 82 deg 52 min 26.7 sec
Latitude = 35 deg 11 min 54.5 sec
Elevation = 896 m

 

GEOMAGNETOMETER MEASUREMENTS. The data is live and updated once a minute.


  • The view to the northwest, showing the geomagnetometer and power panel with Buildings 14, 32 and 30 in the background.

The instrument measures the earth’s magnetic field vector at PARI’s location. It is used to mainly to monitor the effect of solar activity on the field. The parameters of the three dimensional field are displayed and explained below. The instrument uses 3 flux gate type magnetometer sensors oriented 90 degrees to each other and aligned with respect to geographic north, east and zenith. The instrument is located outside on the PARI campus away from the buildings and large equipment. It is entirely solar powered. Raw data from the sensors are transmitted via fiber optics to a desktop computer in the operations room in building one for processing and 1 minute averages are displayed. The data is also archived to the PARI data center.

PARAMETER DEFINITIONS:

Magnitude (F): The strength of the magnetic field vector in nanoTeslas.

Declination (D): The deviation angle in degrees of the horizontal component of the field from true geographic north. A negative angle is west of true north and positive is east.

Inclination (I): The angle in degrees of the field with respect to the local horizontal plane. A positive angle indicates the field direction is into the earth.

Sensor Temperature: The temperature in degrees Farenheit inside the sensor box which is used to correct for the sensor’s temperature dependence.

Vector


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Sensor Calibration:

Each sensor was individually calibrated using a cylindrical insulated wire coil wrapped around a PVC tube inside which the sensor was inserted. The magnetic field inside the tube center was calculated from the known current through the coil and the coil dimensions. The coil was inside a water jacket made from a larger diameter PVC pipe section through which water at different temperatures flowed. The coil was oriented perpendicular to the earth’s field to null this from the sensor. A set of calibration measurements of sensor output vs. magnetic field over a range appropriate for each sensor was derived at different temperatures. A power law curve was fit to each set at each temperature for each sensor. These were then used by the software processing the sensor outputs by the desktop PC to correct for the sensor’s temperature dependence.

Sensor Platform Alignment:

The sensor platform consists of 2 triangular shaped parts, one on top of the other. The bottom part has 3 nylon bolts used for level adjustment. The top part, to which the 3 sensors are mounted, can rotate for azimuth adjustment. The platform is leveled using a bubble level and an electronic level meter. The azimuth is adjusted by taking a sighting on the star Polaris. A specially built sight is used by placing it on the top part of the platform, lining up alignment marks on the platform and the sight, lining up 2 vertical bars on the sight and rotating the top platform part so that Polaris, which is viewed through a mirror, is in the correct position with respect to the vertical bars, depending on the orientation of Ursa Minor (the Little Dipper) at the time of viewing. Polaris is not exactly coincident with the North Celestial Pole but is about 1.2 degrees off.

Links:

For more information about Geomagnetism, go to these sites:

www.ngdc.noaa.gov/geomag

http://geomag.usgs.gov

www.nationalatlas.gov/articles/geology/a_geomag.html


The following people contributed to this project:

Geomagnetometer design, construction, calibration and set up: Ron Speer
Fiber optics and solar power: Lamar Owen, Ben Goldsmith, Donne Curto and Ron Speer
Software: Ron Speer, Michael Castelaz and Menelik Zafir