| The NOAA National Centers for Environmental Information (formerly National Geophysical
Data Center) / World Data Center, Boulder maintains an active database of worldwide
geomagnetic observatory data. Historically, magnetic observatories were established
to monitor the secular change (variation), of the Earth?s magnetic field, and this
remains one of their most important functions. This generally involves absolute measurements
sufficient in number to monitor instrumental drift and to produce annual means. While
the current global network of geomagnetic observatories involves over 70 countries
operating more than 200 observatories, the historic database includes observations
from more than 600 observatories since the early 1800s. The magnetic observatory data
are crucial to the studies of secular change, investigations into the Earth?s interior,
navigation, communication, and to global modeling efforts. The Earth?s magnetic field
is described by seven parameters. These are declination (D), inclination (I), horizontal
intensity (H), vertical intensity (Z), total intensity (F) and the north (X) and east
(Y) components of the horizontal intensity. By convention, declination is considered
positive when measured east of north, inclination and vertical intensity positive
down, X positive north, and Y positive east. The magnetic field observed on Earth
is constantly changing. |