Physical > Magnetic Model
Raster > Physical > Magnetic Model
Data Source: NOAA > National Geospatial-Intelligence Agency > World Magnetic Model
Website: https://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
Description
The World Magnetic Model is the standard model used by the U.S. Department of Defense, the U.K. Ministry of Defense, the North Atlantic Treaty Organization (NATO) and the International Hydrographic Organization (IHO), for navigation, attitude and heading referencing systems using the geomagnetic field. It is also used widely in civilian navigation and heading systems. The model, associated software, and documentation are distributed by NCEI on behalf of NGA. The model is produced at 5-year intervals.
The WMM consists of a degree and order 12 spherical-harmonic main (i.e., core-generated) field model comprised of 168 spherical-harmonic Gauss coefficients and degree and order 12 spherical-harmonic Secular-Variation (SV) (core-generated, slow temporal variation) field model. The Earth's magnetic field, as measured by a magnetic sensor on or above the Earth's surface, is actually the sum of magnetic fields generated by a variety of sources. These fields are superimposed on each other and through inductive processes interact with each other. The most important of these geomagnetic fields are:
1 The Earth's main magnetic field generated in the conducting, fluid outer core.
2 The crustal field generated in Earth's crust and upper mantle.
3 The combined disturbance field from electrical currents flowing in the upper atmosphere and magnetosphere, which induce electrical currents in the sea and ground.
The observed magnetic field is a sum of contributions of the main field (varying in both time and space), the crustal field (varies spatially, but considered constant in time for the time-scales of the WMM), and the disturbance fields (varying in space and rapidly in time). Earth's main magnetic field dominates, accounting for over 95% of the field strength at the Earth's surface. Secular variation is the slow change in time of the main magnetic field. The WMM represents only the main geomagnetic field.
To create an accurate magnetic field model, it is necessary to have vector component measurements with good global coverage and low noise levels. The European Space Agency's SWARM satellite's mission is presently the most suitable magnetic observing system. Also available are ground observatory hourly mean data, although with poorer spatial coverage. The observatory data can provide valuable constraints on the time variations of the geomagnetic field.
There are 8 overlays available: Geomagnetic Longitude and Latitude, Geomagnetic Declination, Geomagnetic Inclination, Geomagnetic Total Intensity, Geomagnetic Horizontal Intensity, Geomagnetic Vertical Intensity, Geomagnetic North Component, Geomagnetic East Component, selectable through the 'Additional Layer Features' control on the 'Layers Menu'.
For more information, see the Geomagnetism Frequently Asked Questions Page: https://www.ngdc.noaa.gov/geomag/faqgeom.shtml#General
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