Coordinate System
Global studies require all data to be rotated into a common known coordinate
system. Data provided to SuperMAG from the colla-
borators are typically in either:
-
Geographic coordinates (north (X), east (Y), vertical down (Z))
-
Geographic
coordinates (horizontal intensity (H), declination (D) and vertical down (Z))
- Geomagnetic
coordinates (magnetic north (H), magnetic east (D) and vertical down
(Z))
with or without baselines subtracted. During intitial setup the sensor axes
are oriented in either the geographic or local magnetic
coordinate system. The Earth main field, however, is constantly changing so
geomagnetic coordinate system are time dependent.
The uncertainties in mind SuperMAG decided to make no assumptions as to the
initial setup of the magnetometer other than the
Z-axis is vertical. Using the two horizontal components SuperMAG determines
a time dependent declination angle and subsequently
rotates the horizontal components into a local magnetic coordinate
system for which the magnetic east component (E) is
minimized and the magnetic north component (N) is maximized. Note that geomagnetic
coordinates are routinely labeled HDZ
although the units of the D-component can be nT or an angle. Likewise, the
D-component is often found to have a significant offset.
As a consequence SuperMAG decided to denote the components:
| B=(BN , BE , BZ) |
where
N-direction is local
magnetic north
E-direction
is local magnetic east
Z-direction
is vertically down
by definition the
offset of the E-component is zero. This reference system is independent of
the actual orientation of the two horizontal
magnetometer axis´s and the data can be rotated to any
desired coordinate system using an appropriate IGRF model.