Enhanced Magnetic Model (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 790, resolving magnetic anomalies down to 51 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 EMM2017 includes data from the European Space Agency'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.

The EMM2017 model has been updated with improved crustal and core field parts based on the latest track line and satellite magnetic data. The crustal field model of EMM2017 was derived from the latest (2017) release of EMAG2-v3, the Earth Magnetic Anomaly Grid at 2-arcminute resolution, version 3. It is of higher spatial resolution (degree and order 790 of the spherical harmonic expansion) than the crustal field model of EMM2015. The largest differences between these two crustal field models are located in oceanic areas and reflect different methodologies for constructing the underlying EMAGs. We updated the core field (degree and order from 1 to 15) part of EMM2017 based on the Swarm satellite magnetic data. EMM2017 is valid from 2000.0 to 2022.0.

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.

Acknowledgments

Changes to the code

EMM - Coefficients and Grids