The World Magnetic Model - Uses
Compasses have been used for several thousand years to determine direction. They point in
the direction of magnetic force at the user’s location, and the direction it points is, more often
than not, in a different direction than geographic north (toward the North Pole), a more
precise direction is achieved by knowing the angle between them (magnetic declination).
However, declination changes with location and time, and a geomagnetic model is often used
to correct for it. Since the changes in geomagnetic fields are difficult to predict, timely model
updates (every 5 years for the WMM) are required for navigational accuracy. The WMM
satisfies all these criteria and is therefore widely used in navigation. Examples include, but
are not limited to, ships, aircraft and submarines. Magnetometer based attitude (roll and pitch)
control is commonly used in aircraft and satellites.
Why do we need magnetic navigation when Global Position System (GPS) is readily
available? GPS provides precise point location but only measures travel direction when in
constant motion. A GPS receiver must collect several sets of latitude and longitude pairs to
obtain direction. In addition, GPS signals may become blocked due to obstructions, adverse
terrestrial and space weather, ionospheric conditions or being underwater or underground.
Hence, compasses complement GPS receivers to attain precise and immediate navigational
headings for air, ground, and water-based systems. Electronic compasses and the WMM
commonly co-exist in GPS receivers.
Antennas and Solar Panels
Antennas (e.g. satellite dish television) and solar panels often need to be precisely oriented for
maximum performance. The WMM’s declination information for specific locations is often
employed by companies to orient their products correctly.
While the traditional use of the WMM is for navigation, it is now acquiring new utilities in consumer electronic devices with built-in digital compasses. Many of the new generations of smart phones and digital cameras take advantage of the WMM to estimate bearing. The availability of low-cost, small, and energy efficient electronic compasses allow for magnetic direction in portable electronics to be common place. This new user group will significantly increase the demand for WMM models in the near future. NGDC has developed an application called CrowdMag that allows users to collect their own magnetic field data using the magnetometers in their phone. This app sends data anonymously back to NOAA so it can be used to help validate and expand future magnetic models.
Airborne and marine magnetic surveys are used by oil and mineral exploration companies to
detect magnetic signals from the Earth’s crust. These small amplitude signals (typically 100s
of nT), must be separated from the large main magnetic field (typically 20,000 to 60,000 nT).
Geomagnetic models are used by companies to extract these small magnetic signals from the
survey records. A new application is the use of geomagnetic models for directional drilling.
Oil wells are often drilled horizontally from a conveniently located platform. An electronic
compass located behind the drill head (bit) provides the engineers with accurate orientation of