Enhanced Magnetic Model (EMM2015)
Declination Comparison of WMM and EMM
The Earth's internal magnetic field is a superposition of the field generated by the geodynamo in the liquid outer core (main field) and the field of magnetized rocks in the crust and upper mantle. The main field dominates the long wavelengths, whereas the crustal field dominates at wavelengths smaller than 2500 km.
Geomagnetic field models are conveniently represented as spherical harmonic expansions of a scalar magnetic potential. Such a model can then be evaluated at any desired location to provide the magnetic field vector, its direction, and strength. The standard World Magnetic Model uses a spherical harmonic representation to degree and order 12, resolving the magnetic field at 3000 km wavelength. In contrast, the Enhanced Magnetic Model (EMM) extends to degree and order 720, resolving magnetic anomalies down to 56 km wavelength (see comparison in the figure). The higher resolution of the EMM results in significantly improved pointing accuracy.
The EMM model was compiled from satellite, marine, aeromagnetic and ground magnetic surveys. The EMM 2015 includes data from The European Space Angency's Swarm satellite mission. This constellation of satellites currently represents the best source of data about the evolution of the Earth's main magnetic field.
Why is this important?
Many different applications utilize Earth's magnetic field, whether for navigation, resource evaluation, or research. The magnetic field experienced at or near the Earth's surface is a combination of the main magnetic field, the relatively static crustal magnetic field, and the rapidly time-varying external magnetic field. The better we are able to define these fields, the more accurate the results.
EMM - Coefficients and Grids
The NGDC-720 research model preceded the Enhanced Magnetic Model. The NGDC-720 will not be updated. The archived model and coefficients are provided for software evaluation and testing purposes.