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| World Magnetic Model | |
|---|---|
| Name | World Magnetic Model |
| Established | 2014 (current cycle) |
| Authority | National Geospatial-Intelligence Agency; British Geological Survey |
| Type | Geomagnetic field model |
World Magnetic Model The World Magnetic Model is a global representation of Earth's magnetic field used for navigation, surveying, and scientific analysis. It provides coefficients for computing magnetic declination, inclination, and intensity across the planet, serving civil, military, and commercial systems that rely on compass-based orientation. Developed and maintained through collaboration among agencies including the National Geospatial-Intelligence Agency and the British Geological Survey, the model underpins devices from smartphones to naval vessels and aviation instruments.
The model supplies spherical harmonic coefficients that describe the main geomagnetic field and its secular variation, enabling conversion among magnetic declination, magnetic inclination, and magnetic flux density components at any geographic location and altitude. Primary users include Federal Aviation Administration, International Civil Aviation Organization, NATO, and manufacturers such as Apple Inc., Garmin, and Boeing that embed the model in navigation systems. It supports mapping efforts by agencies like the United States Geological Survey and operations of polar platforms such as McMurdo Station and vessels like USS Constitution. The model informs research conducted by institutions including the Scripps Institution of Oceanography, Columbia University, and the Lamont–Doherty Earth Observatory.
Origins trace to early geomagnetic surveys by explorers such as James Clark Ross and scientists at institutions like the Royal Society and Uppsala University. The formal, regularly updated global model evolved from academic efforts at Carnegie Institution for Science and operational programs in the United States Navy and Royal Navy. During the Cold War, collaboration between National Oceanic and Atmospheric Administration and military bodies expanded into the contemporary model maintained by the National Geospatial-Intelligence Agency and the British Geological Survey. Updates have paralleled advances in satellite missions such as Ørsted (satellite), CHAMP (satellite), SWARM (ESA mission), and GOCE (satellite), and benefited from ground observatories like INTERMAGNET stations and historical records from expeditions including the Challenger expedition.
The model is expressed as a truncated spherical harmonic expansion with Gauss coefficients (g_nm, h_nm) representing field contributions from internal sources primarily in the Earth's core and parameterized secular variation terms. Practically, it includes degrees and orders up to 12 or 13, balancing computational cost and accuracy for users ranging from handheld compasses to aircraft avionics certified by Federal Aviation Administration and European Union Aviation Safety Agency. Computation uses geodetic coordinates tied to reference systems such as WGS 84 and the International Terrestrial Reference Frame. Numerical implementations appear in software libraries used by Esri, QGIS, MATLAB, and languages like Python (programming language) and C++ for integration in platforms by Lockheed Martin and Thales Group.
Inputs combine satellite magnetometer data from missions by agencies such as the European Space Agency, NASA, and German Research Centre for Geosciences with observatory records from networks like INTERMAGNET and marine and airborne surveys conducted by organizations including NOAA and the United States Geological Survey. Historical geomagnetic observatory series from institutions such as Greenwich Observatory and expedition logs from explorers like Ferdinand Magellan and Captain James Cook inform long-term secular variation. Measurements incorporate instrumentation standards developed at laboratories like National Institute of Standards and Technology and calibration routines from companies such as Honeywell and Northrop Grumman.
Operational navigation for civil aviation and maritime shipping depends on the model for runway magnetic headings by agencies including ICAO and port authorities like Port of Singapore Authority. Military systems in United States Department of Defense platforms and NATO assets use it for targeting, geolocation, and weapon systems by contractors such as Raytheon Technologies. Consumer electronics from Samsung and Sony and mapping services by Google and HERE Technologies rely on the model for compass apps and augmented reality. Scientific applications span paleomagnetism at universities like California Institute of Technology, geodynamo modeling at Princeton University, and space weather studies at Space Weather Prediction Center and Imperial College London.
The model is typically updated on a four- or five-year cycle, with interim Correction Models issued when secular variation exceeds specifications. Maintenance involves collaboration between the National Geospatial-Intelligence Agency and the British Geological Survey and consultation with stakeholders such as FAA and ICAO. Accuracy metrics are validated against independent observatory data from INTERMAGNET and satellite cross-comparison with SWARM; formal performance is documented in technical briefings to agencies like NGA and standards bodies such as ISO. Software toolkits from vendors including Esri and open-source projects like PROJ implement the model and provide user advisories.
Limitations stem from coarse temporal resolution of secular variation, inability to represent rapid geomagnetic jerks observed by research at University of Leeds and University of Alaska Fairbanks, and reduced accuracy in high-latitude and polar regions where external current systems such as the auroral electrojet influence measurements. Controversies include debates over update cadence during periods of accelerated secular change reported by Nature (journal) and Science (journal), implications for military reliance highlighted in briefings to United States Congress, and challenges integrating near-real-time data from commercial satellite constellations like Spire Global and Planet Labs. Critics in the academic community, including researchers at University of Oxford and ETH Zurich, have called for expanded open data access and more frequent revision schedules.
Category:Geomagnetism