The Earth’s magnetic field has been used for navigation since ancient times. Magnetic navigation has continued to improve alongside transportation technologies so that now magnetic models are used in planes, ships and even in your smartphones. To improve magnetic navigation, NOAA scientists at the National Geophysical Data Center (NGDC) in Boulder, Colorado, have tracked the changing magnetic field using satellites to provide the most accurate and reliable models so that users can navigate their world with ease and precision. The World Magnetic Model (WMM) is NGDC's newest spherical harmonic model of the magnetic field produced by the Earth's core and will accurately represent the main magnetic field on Earth for the next five years.
Introduction to the World Magnetic Model
The WMM is a large-scale representation of Earth's magnetic field that gives analog and digital magnetic compasses dependable accuracy. It is used extensively in smartphone apps as an accurate way to know which way the user is going.
Using years worth of satellite data, NOAA's NGDC are able to model Earth's changing magnetic field and predict what it will look like over the next five years. Produced every five years since 1975, this model of the magnetic field produced by Earth's rapidly spinning metallic core has been critical in aiding navigation for the military, scientific exploration, nautical charting and citizen transportation. Since 2005, NGDC has worked closely with the British Geological Survey (BGS) to provide the most accurate models that are used for the myriad of navigational uses across the globe.
The World Magnetic Model continues to be the navigation standard model for the entire U.S. Department of Defense (DOD), the North Atlantic Treaty Organization (NATO), International Hydrographic Organization (IHO), Federal Aviation Administration (FAA), and consumer electronics (e.g., iOS, Blackberry, Android) and many others.
Online Magnetic Calculators
NGDC provides multiple online tools and softwares to estimate current and past values of the magnetic field:
- Declination Calculator: magnetic declination (variation) for a single day anytime between 1590“present.
- Magnetic Field Calculator: all seven magnetic field components (X, Y, Z, H, D, I and F) for a single location on a single day to a range of multiple years from 1590“present.
- Magnetic Field Properties Grid Calculator: estimated values of Earth’s magnetic field, including magnetic declination (D), based on the current WMM or the International Geomagnetic Reference Field (IGRF) for a grid of locations over a single day to multiple years.
- U.S. Historic Declination Calculator: for the conterminous U.S. from 1750“present. It uses a combination of a historic polynomial model and the IGRF spherical harmonic models.
Each day these online calculators are used to make over 25,000 queries into the status of the Earth's past and present magnetic field by a wide variety of users. They are used to survey historic property boundaries, help hikers correct their compasses, and aid in the understanding of animal migrations such as whales, birds and butterflies.
CrowdMag App”Citizen Science!
Using smartphones, NOAA can gather more data about the geomagnetic field than ever before. We have created a way to turn your smartphone into a traveling magnetic observatory! Citizen scientists can download NOAA's CrowdMag application to turn the millions of smartphones spread across the globe into mobile scientific instruments. This will help all of us to understand the amazing forces and complexity of Earth's magnetic field.
The magnetometer that shows you which way you are going on your navigation app can also be used to measure the magnetic field that always surrounds us. The CrowdMag app developed by NGDC will send this data anonymously back to NOAA to help us verify and improve our magnetic models and create more accurate models in the future.
The CrowdMag app also includes a calculator that uses the WMM to provide magnetic declination, dip angle, total field and other magnetic field components for any date or location. The CrowdMag app is available for iOS and Android systems.
Commercial Applications and Uses
The WMM is the navigational model used by all commercial ship and aircraft operating in the U.S. in addition to all military ship, aircraft and GPS units within NATO and beyond. The WMM is also used by space agencies, like NOAA, to slow the rotation of newly launched satellites to enable the star cameras to get a fix for positioning.
Some applications include:
- Ships and Submarines
- Magnetic Silencing (Degaussing)
- Anti-Submarine Warfare Magnetic Anomaly Detection (MAD)
- Navigation under the Arctic Ice
- Bias-drift Correction of Fiber Optic Gyros
- Horizontal Drilling
- Calibration of Ground and Space-based Magnetometers
- AFRL/NASA Communication and Navigation Outage Forecast Satellite
Unlike GPS devices, which rely on line of sight to satellites thousands of miles above the Earth, WMM-corrected magnetic compasses cannot be jammed, are not subject to ionospheric disturbances, and work everywhere across the globe, including under the sea and in deep canyons.