90 GSM19 Series Magnetometers - Version 7
GEM Systems, Inc. Advanced Magnetometers
For more technical information, visit www.gemsys.ca
APPENDIX A: GLOBAL MAGNETIC MAPS
Official International Geophysical Reference Field (IGRF) maps of the total magnetic field and its
inclination are shown in Figures A1 and A2.
Refer to map A1 to estimate the total magnetic field of your survey area.
On map A2, areas with inclination more than +/- 45
0
are considered “ polar” areas, while those
with less than +- 45
0
inclination are “equatorial” areas -- although some parts of “equatorial” areas
lay far away from geographic equator (i.e. almost all of South America and most of Africa).
A.1 UNDERSTANDING THE DIFFERENT SENSOR ORIENTATIONS
A.1.1 Overhauser Sensor
In equatorial regions, the magnetic field direction should be considered horizontal and pointing
north to south. Here, the GSM-19 (Overhauser) sensor axis must be oriented horizontally in an
east-west direction. In regions north of the +45
o
line, or south of the -45
o
line, the sensor may be
oriented in any horizontal direction.
NOTE:
Omnidirectional sensors are available for carefree operation. Please ask your
GEM representative for more information.
A.1.2 Standard Proton Sensor
GSM-19T (standard proton magnetometer) sensor is constructed differently. It has an “orientation
line” engraved at its side. In polar regions this line must be vertical and in equatorial regions it is to
be horizontal. Alternatively the orientation line can be kept vertical and the sensor in principally
North-South orientation for the whole Earth.
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