The World Magnetic Model (or WMM) is a large spatial-scale representation of the earth’s magnetic field that impacts the accuracy of compasses, especially Digital Magnetic Compasses (DMCs) – a type of inertial sensor. The WMM is the standard model used for navigation. The model is used by the US Department of Defense, the UK Ministry of Defence, the North Atlantic Treaty Organization (NATO), the International Hydrographic Organization (IHO), consumer electronics, and is also widely used in civilian navigation and in attitude and heading systems (AHRS). Even our smart phones use the WMM.
The WMM is a joint product of the US National Geospatial-Intelligence Agency (NGA) and the UK’s Defence Geographic Centre (DGC). Scientists at the National Geophysical Data Center (NGDC) in Boulder, CO, track the changes in the earth’s magnetic field to create models that are both accurate and reliable. By continuously surveying the magnetic field, they can then extrapolate changes for the future. The WMM is typically updated every five years with the most recent version released in December, 2019.
The WMM is updated because there are changes in the Earth’s outer core that cause changes in its magnetic field. For example, the North magnetic pole has been drifting towards Siberia for years. This drift, this change, adversely impacts the accuracy of navigation. The WMM updates compensate for these changes and improve navigational accuracy.
The earth’s magnetic field has been used for navigation since ancient times. As technology has advanced, so has magnetic-field navigation. Today it is used in planes, ships, cars, and, as mentioned before, even in smart phones.
Though GPS is a great tool for navigation, it cannot generate heading information when stationary. To determine true direction (or heading), knowledge of the local magnetic field as well as an accurate and reliable map of the earth’s magnetic field is needed. Magnetometers are sophisticated sensors that measure magnetic field strength. Using 3-axis magnetometers together with 3-axis accelerometers, the horizontal and vertical components of the earth’s magnetic field can be accurately calculated and thus provide magnetic heading. If GPS location is also known, the WMM can then be used to convert magnetic heading to true north heading. Attitude Heading Reference Systems (AHRS) incorporate these magnetometers and accelerometers as well as gyroscopes to maintain heading accuracy in dynamic environments.
Download the Latest Version of WMM files for your Sparton Inertial Sensors